Category: Class 7

MP Board Class 7th Science Solutions Chapter 9 Soil

Soil Intext Questions

Question 1.
I wonder why I found some pieces of plastic articles and polythene bags in the soil sample collected from the roadside and the garden?
Answer:
It is because people throw used plastic things and polythene bags in the soil.

Question 2.
I want to know whether ‘the soil from a field can be used to make toys?
Answer:
Yes.

Question 3.
I want to know: What kind of soil should be used for making making  and surahis?
Answer:
Clayey soil.

Question 4.
Boojho wondered why there was a difference in the absorption of water in the two squares?
Answer:
Because different soils are used to make the two squares.

Question 5.
What is the difference between rate of percolation and the amount of water retained?
Answer:
Rate of percolation is the amount of water percolated per unit time through soil. Whereas the amount of water retained is the amount of water absorbed by soil. Thus, rate of percolation and water retention are opposite attributes.

Activities

Activity 1
Collect some soil samples and observe them carefully. You can use a hand lens. Examine each sample carefully and fill in Table. Answer:
Table

Activity 2
Take a little soil. Break the clumps with your hand to powder it. Now take a glass tumbler, three quarters filled with water, and then add a handful of soil to it. Stir it well with a stick to dissolve the soil. Now let it stand undisturbed for some time. Afterwards, observe it and answer the following questions:

1. Do you see layers of particles of different sizes in the glass tumbler?
2. Draw a diagram showing these layers?
3. Are there some dead rotting leaves or animal remains floating on water?

Answer:

1. Yes
2. 
3. Yes

Activity 3
Find from your teachers, parents and farmers the type of soils and crops grown in your area. Enter the data in the following Table,

1. Which kind of soil would be most suitable for planting rice?
2. Soil with a higher or lower rate of percolation?

Answer:

1. Loamy soil.
2. Lower rate of percolation.

Soil Text Book Exercises

Tick the most suitable answer in questions 1 and 2.

Question 1.
In addition to the rock particles, the soil contains?

1. Air and water
2. Water and plants
3. Minerals, organic matter, air and water
4. Water, air and plants.

Answer:
3. Minerals, organic matter, air and water.

Question 2.
The water holding capacity is the highest in?

1. Sandy soil
2. Clayey soil
3. Loamy soil
4. Mixute of sand and loam.

Answer:
2. Clayey soil.

Question 3.
Match the items in Column I with Column II:

Answer:

(i) (b)
(ii) (c)
(iii) (a)
(iv) (e)
(v) (d).

Question 4.
Explain how soil is formed?
Answer:
The soil is the mtter which cover the top most layer of the earth in most of area. It is one of the most important natural resources. Long ago earth was a very hot sphere and then converted into a very hard and rocky land. These rocks were broken into smaller pieces by violent earthquakes. Volcanic eruptions also made the rocks and lava into smaller pieces. In cold temperatures the ice in the services of rocks expanded to break it into smaller pieces and thus gradually the soil was formed. The nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.

Question 5.
How is clayey soil useful for crops?
Answer:
Clayey soil is good at retaining water. They, are rich in humus and are very fertile. They also hold sufficient water due to the presence of smaller particles and certain enough air due to the presence of some large particles.

Question 6.
List the differences between clayey soil and sandy soil?
Clayey soil:

1. They contains more than 50% of clay particles.
2. Water holding capacity is very high.
3. Suitable for plant growth.
4. Low percolation rate.

Sandy Soil:

1. They contains about 60% of sand particles.
2. Water holding capacity is very low.
3. Not suitable for plant growth.
4. High percolation rate.

Question 7.
Sketch the cross section of soil and label the various layers?
Answer:

Question 8.
Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Answer:
We know that,

Thus, the rate of percolation is 5ml/min.

Question 9.
Explain how soil pollution and soil erosion could be prevented?
Answer:
Polythene bags and plastics pollute the soil. They also kill the organisms living in the soil. That is why there is a demand to ban the polythene bags and plastics. Other substances which pollute the soil are a number of waste product, chemicals and pesticides. Waste products and chemicals should be treated before they are released into the soil.

The use of pesticides should be minimised. Soil erosion can be slowed down and soil can be conserved by regulating the factors responsible for it. Some methods to prevent or slow down the soil erosion are:

1. To stop the unnecessary cutting of forests and trees.
2. To stop the excessive use of grass land due to overgrazing by cattle.
3. Growing vegetation along the boundary of the fields and open grounds.
4. Making use of proper and scientific methods for cultivation such as crops rotation. This maintains the natural fertility of the soil and at the same time soil also maintains its capacity to hold water. Soil remains wet and cannot be easily carried away by water and blown up by wind.
5. Making use of scientific methods for irrigation and water drainage.
6. Gutting the hill slopes into steps or terraces and adopting terrace cultivation on hill slopes.

Question 10.
Solve the following crossword puzzle with the clues given:

Across:

2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.

Down:

1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.

Answer:

Soil Additional Important Questions

Soil Objective Type Questions

Question 1.
Choose the correct alternative:

Question (i)
The constituents of the soil are –
(a) Mineral particles, air and water
(b) Living of organisms
(c) Organic and inorganic substances
(d) All of these.
Answer:
(d) All of these.

Question (ii)
Soil is the thin layer of fine material containing –
(a) Organic matter
(b) Air and water
(c) Weathered rock materials
(d) All of these.
Answer:
(d) All of these.

Question (iii)
Soil formation is brought about by –
(a) physical factors
(b) Chemical factors
(c) Biological agent
(d) All of these.
Answer:
(d) All of these.

Question (iv)
Which profile contains humus –
(a) A – horizon
(b) B – horizon
(c) C – horizon
(d) R – horizon.
Answer:
(a) A – horizon

Question (v)
Which of these has the smallest size of particles –
(a) Sand
(b) Silt
(c) Clay
(d) Gravel.
Answer:
(b) Silt

Question (vi)
What kind of soil is best for growing cotton –
(a) Black soil
(b) Alluvial soil
(c) Red laterite soil
(d) Mountain soil.
Answer:
(a) Black soil

Question (vii)
What kind of soil is good for growing tea and coffee –
(a) Red laterite soil
(b) Black soil
(c) Laterite soil
(d) Mountain soil.
Answer:
(c) Laterite soil

Question (viii)
The dead and decaying organisms are –
(a) Humus
(b) Gravel
(c) Clay
(d) Inorganic material.
Answer:
(a) Humus

Question (ix)
Which kind of soil is best for growing wheat, rice and sugarcane –
(a) Black soil
(b) Mountain soil
(c) Alluvial soil
(d) Desert soil
Answer:
(c) Alluvial soil

Question 2.
Fill in the blanks:

1. Wheat and rice grow best in …………… soil.
2. Humus is present in the ………….. layer of soil, known as the ………….. horizon.
3. Clay is the smallest size of particles less than …………… in diameter.
4.  …………… is a mixture of sand, silt, clay and humus.
5. Weathering of rocks is a …………… process.
6. …………… is the breaking down of rocks into smaller pieces.
7. Soil commonly found in India is of …………….. main types.
8. Red colour of the soil is due to ………………

Answer:

1. Alluvial
2. Upper, A
3. 0.002 mm
4. Loam
5. Slow
6. Weathering
7. Six
8. Iron.

Question 3.
Which of the following statements are true (T) or false (F):

1. The soil is uppermost layer of the land surface.
2. The soil with particle size greater than 2 mm in diameter is gravel.
3. The soil with particle size greater than 2 mm in diameter is clay.
4. Decayed organic matter in the soil forms humus.
5. Most fertile farm lands consist of alkaline soil.
6. No humus is present in C – horizon.
7. Black soil is rich in iron and magnesium.
8. B – horizon is the most fertile part of the soil.
9. Laterite soil is rich in nutrients.
10. Soil is classified in sand, silt and clay.
11. The process of .carrying away of top soil by natural process is called soil erosion.
12. Black soil is loamy in texture with plenty of humus.
13. Overgrasing is a means of soil conservation.
14. Extremely acidic soil supports plants.
15. Planting of trees in a large area is known as afforestation.

Answer:

1. True (T)
2. True (T)
3. False (F)
4. True (T)
5. False (F)
6. True (T)
7. True (T)
8. False (F)
9. True (T)
10. True (T)
11. True (T)
12. False (F)
13. False (F)
14. False (F)
15. True (T).

Match the items in Column A with items in Column B:

Answer:

(i) (d)
(ii) (c)
(iii) (a)
(iv) (b)
(v) (e).

Soil Very Short Answer Type Questions

Question 1.
Mention two main components of soil?
Answer:
The two main components of soil are mineral particles and organic particles.

Question 2.
Name the different types of particles present in the soil?
Answer:
The different types of particles present in the soil are water, air, humus, mineral particles and living organisms.

Question 3.
What is soil?
Answer:
The soil is the outer layer of earth’s crust capable of supporting plant growth.

Question 4.
Mention two functions of soil?
Answer:
The two functions of soil are:

1. It provides water and minerals to the plants.
2. It provides anchorage to the plants.

Question 5.
What is the role of plants in the formation of soil?
Answer:
The roots of plants on penetrating into the crevices of rocks break these and help in the formation of soil.

Question 6.
Name some of the living organisms which are present in the soil?
Answer:
Fungi, bacteria, earth worms, round worms, and protozoams are the living organisms present in the soil.

Question 7.
What do you mean by soil texture?
Answer:
The structure or texture of soil determines the relative proportion of particles of different sizes.

Question 8.
What is the difference between soil texture and structure?
Answer:
Soil texture pertains to particle size, composition of a soil and soil structure refers to arrangement of soil particles into aggregates.

Question 9.
What is meant by the term weathering?
Answer:
Weathering is the breaking down of huge pieces of rocks into smaller pieces by the action of natural forces, such as water, wind, glaciers and roots of plants.

Question 10.
Which layer of soil contains the largest rock pieces?
Answer:
Bedrock contains the. largest rock pieces.

Question 11.
Which layer of soil will have the highest humus content and which the least?
Answer:
The upper most layer (A-horizon) will have the highest humus content and lowest layer (C-horizon) will have the least.

Question 12.
Which types of soil is most suitable for crops like wheat, rice and sugarcane?
Answer:
Alluvial soils is the most suitable for crops like wheat, rice x – and sugarcane.

Question 13.
Define residual soil?
Answer:
The soil which remains at the place of its formation is called residual soil.

Question 14.
Which soil is classified as alluvial type?
Answer:
The soil transported by flowing water is classified as alluvial type.

Question 15.
What are mountainous soil?
Answer:
Mountainous soil consist of clay, shales, sandstones and limestones. This type of soil is usually found in depressions and valley basins or on gently inclined slopes.

Question 16.
Define loam?
Answer:
Loam is a mixture of sand, silt and clay and also has humus in it.

Question 17.
What is soil pollution?
Answer:
The contamination of soil with excess of fertilizers, herbicides, weedicides, insecticides and industrial waste is called soil pollution.

Question 18.
Define soil moisture?
Answer:
Soil holds water in it, which is called soil moisture.

Question 19.
Name the three types of soil erosion?
Answer:
The three types of soil erosion are sheet erosion, gaily erosion and wind erosion.

Question 20.
How does vegetation help to prevent soil erosion?
Answer:
Flowing water and wind take away the top layer of the soil if there is no vegetation. The grasses, trees hold the soil in place.

Question 21.
How does soil erosion take place?
Answer:
Soil erosion can take place by natural processes such as floods, forest fire, winds, deforestation and overgrazing.

Question 22.
Which horizon of soil profile contains humus?
Answer:
A – horizon of soil profile contains humus.

Question 23.
Which type of soil is classified as residual soil?
Answer:
The soil, which remains at the place of its formation is called residual soil. This type of soil is generally poor in nitrogen, phosphorus and humus.

Question 24.
The soil at a given place was found to consist of sand stones, clay, shales and limestone. What is the type of the soil and how it might have formed?
Answer:
The type of the soil is mountainous soil. It might have formed, when the weathered soil particles are taken away to other places.

Soil Short Answer Type Questions

Question 1.
What does soil consist of?
Answer:
Soil consists of tiny bits of mineral particles which come from larger rocks and humus which is dark brown in colour and consists of decaying remains of plants and animals. Soil also contains water, air and living organisms such as bacteria, fungi, earth worms, round worms, and insects etc.

Question 2.
How is the soil formed? Explain in brief?
Answer:
Millions years ago, the surface of earth was very hard, rugged and rocky. In the long run, weathering of these rocks resulted in formation of soil which with the flow of river water came down to the lower plains and got deposited. Gradually it spread out on whole surface of the earth. Formation of soil is a very slow process. In this process rocks crack and break down into fine particles to form soil.

Question 3.
Define alluvial soil and its distribution?
Answer:
Alluvial soil is loamy soil which contains abundant amount of water in it. This is very fertile soil. This type of soil is very suitable for the production of wheat and rice. This soil is found in the plains of northern India, i.e., in the state of Punjab, Bihar, Haryana, Uttar Pradesh and West Bengal.

Question 4.
What are physical properties of soil?
Answer:
The physical properties of soil are:

1. Colour
2. Moisture storage capacity
3. Texture
4. Presence of living organisms
5. Porosity.

Question 5.
Give an account of the importance of physical properties of soil?
Answer:
The physical properties .of soil exert a great influecne on soil fertility. These are taken into consideration when soil is to be used as a medium for plant growth but also when soils are to be [ used as a structural material for making highways, dams, foundation for buildings as well as for the manufacture of bricks and tiles.

Question 6.
What are organic and inorganic components of soil?
Answer:
The inorganic components of soil comprise minerals which are derived from fragmentation and weathering of rocks. The porespaces formed between the mineral particles of soil are filled with water and gases. The organic component of soil comprise organic wastes, dead animals, plants and their decomposition products.

Question 7.
Explain the role of various organisms present in the soil?
Answer:
Bacteria in the soil helps in decomposing dead remains of plants and animals to make humus. Some bacteria can convert atmospheric nitrogen into water soluble nitrates which plants can easily use for their growth. Earthworms help in loosening of soil. They also improve the texture of the soil thus causing better growth of plants.

Question 8.
Name four common sources of pollution of soil?
Answer:
The common sources of pollution of soil are:

1. Excessive use of fertilisers.
2. Spraying of crops with insecticides and herbicides.
3. Garbage and other kitchen refuge.
4. Industrial wastes such as chemicals, plastic, leather, fly ash, etc.

Question 9.
Define A – horizon layer. Give also the main characteristic of A – horizon.
Answer:
A – horizon layer:
The uppermost layer of the soil is called A – horizon. It is generally known as upper soil or earth’s crust. The main characteristics of this layer of soil are as under:

1. It generally bears dark colour.
2. It contains lot of dead and decaying plant and animal matter called humus.
3. Due to presence of humus this layer is highly fertile.
4. The soil in this layer is porous, soft and has comparatively more water retaining capacity.
5. In this layer living organisms such as earth worms, insects, bacteria and fungi etc. are found.

Question 10.
Define B – horizon layer. Also give the main characteristics of B – horizon.
Answer:
B – horizon layer:
This layer lies next to A – horizon. The main characteristics of this layer of soil are as under:

1. The colour of this layer is comparatively dull.
2. This layer of soil is usually harder and more compact than the top soil.
3. This layer contains very less amount of organic matter in it.
4. This layer is rich in iron oxide and soluble mineral salts,
5. Roots of large and old trees are found in this layer.

Question 11.
Differentiate between Alluvial soils and Desert soils.
Answer:
Alluvial soils:

1. Loamy in texture with plenty of humus.
2. Very fertile, good for crops like wheat and rice.
3. In India, it is mainly found in the plains of Uttar Pradesh, Haryana, Bihar, West Bengal and in the coastal regions of Orissa and Andhra Pradesh.

Desert soils:

1. Soil sandy and porous, cannot hold much water.
2. If irrigated, crops can be grown.
3. In India, it is mainly found in Rajasthan and in some parts of Gujarat.

Soil Long Answer Type Questions

Question 1.
Describe the various steps involved in the formation of soil?
Answer:
There is a hard surface of the rocks just below the layer of the soil. In the past, these rocks were broken into smaller pieces by a process known as weathering. Weathering is the breaking down of huge pieces of rocks into smaller pieces by the action of natural forces, such as water, wind, glaciers and roots of plants, etc.

1. Rain water enters crevices of rocks. In winter, as this water freezes, it expands. This expansion breaks the rocks into smaller pieces.

2. The broken pieces roll down by the force of flowing or wind.

3. The broken pieces get converted into very fine particles, and mix with humus to form soil.

4. Roots of tree growing through rocks exert great pressure on the rocks. This causes cracks in the rocks, leading to weathering.

5. Large variation in day and night temperatures.

6. In hot and humid climates, the minerals in rocks react with oxygen of the air. Such oxidised rocks crumble to form soil.

Question 2.
Describe various types of soil on the basis of their classification?
Answer:
There are mainly six types of soil found in India. These are:

1. Red soil:
It is red in colour due to the presence of red iron oxide in it. It is poor in humus but can be made fertile by adding manure. This type of soil is generally found in southern part of. India.

2. Black soil:
It is derived from the lava of volcanic eruptions and is rich in minerals containing iron and magnesium. This type of soil is found in Maharashtra and parts of Madhya Pradesh, Gujarat and Andhra Pradesh.

3. Alluvial soil:
It is a loamy soil which contains abundant amount of water in it. This is very fertile soil. This type of soil is very suitable for the production of rice and wheat. This soil is found in the plains of northern India.

4. Desert soil:
It is grey to brown in colour. The soil is sandy and porous, and cannot hold much water. This soil is found in Rajasthan and Gujarat.

5. Mountain soil:
It has the highest humus content among all soils in India. These soils are highly, fertile. This soil is found in the Himalyan region and the north – eastern parts of India.

6. Laterite soil:
It is red in colour and good for crops such as tea, coffee and coconut. This type of soil is typical of the rainy climate and rich in nutritive elements. This soil is found in Tamil Nadu, Andhra Pradesh, Assam and Orissa.

Question 3.
Write an essay on the importance of soil?
Answer:
Soil is an important part of our earth. It is not only a natural habitat for various worms and insects but plants also grow and absorb water and minerals for their growth and development in the soil.

1. For food, clothing and shelter:
By supporting growth of plants, the soil provides us with food. Much of our clothing, such as cotton and wool, can be traced to the soil. Plants also provide us fuel, paper, medicines and wood for use in furniture and for constructing houses.

2. For minerals:
We depend on the soil for minerals. Industries use the minerals dug out from the earth to extract metals such as gold, silver, iron, etc. and for use in thousands of industries that produce various useful things for us. Minerals, such as petroleum, natural gas, and coal obtained from soil provide us fuel and many other useful things.

3. For clay:
We depend on the soil for clay which is the raw material used to make tiles, bricks, procelain and pottery.

4. For water:
We depend on the soil for water. Water that seeps into the soil is stored underground as subsoil water. We use this water for drinking and other purposes.

Question 4.
Write a note on soil erosion?
Answer:
The process of water or wind carrying away soil from one place to another is called soil erosion. Following are the main reasons for soil erosion:

1. Erosion by natural forces:
Fast moving wind generally . carries away with it the top soil from the surface of the earth. Similarly, heavy rainfall creates flood situation and fast moving water washes away with it the top fertile soils from our fields which combinely result into erosion of soil.

2. Erosion by human activities. Various human activities are responsible for erosion of soil such as cutting of forests, improper and unscientific methods of agriculture and extensive use of grass lands.

Question 5.
What are the main causes for the erosion of soil?
Answer:
The main causes for the erosion of soil are:
1. Cultivation:
Continuous cultivation of land by only one type of crop further adds to the loss of soil fertility. Once the top of soil is lost, the sub-soil becomes a part of the layer for cultivation. This layer has less nutrient retention power, organic matter and aeration.

2. Deforestation:
It is due to increasing population and increasing industrialization. Deforestation leads to flooding and soil erosion. Forested land looses one tonne of soil per year whereas unforested land looses approximately 40 times more soil.

3. Floods:
The soil taken away by flood often gets deposited in ponds, rivers and lakes’. This causes the water to become muddy and reduces the depth of ponds, rivers and lakes. It also raises their bed due to silting, which has an adverse impact on aquatic life.

4.Overgrasing:
Animal overgrase the slopes that leads to removal of vegetation cover from the soil. All these animals pulverise the soil which is easily washed away in time of heavy rainfall. By overgrasing the soil is denuded of its protective covering of roots and grass.

Question 6.
How will you demonstrate that the vegetation prevents erosion of soil?
Answer:
Take two trays or baskets. Fill them with garden soil. Grow grass or some cereal in one of them and water it properly for a few days. Now keep both the trays in a slightly inclined position by placing a brick below their one side. Let the water fall on both the trays. You will find that the water that flows from the tray with vegetation contains less amount of soil particles in it. This is due to the fact that the roots of plants bind the soil and do not allow it to flow with water.

Question 7.
Differentiate between Black soils and Red soils?
Answer:
Black soils:

1. Rich in iron and magnesium derived from basaltic rocks.
2. Soil is clayey, contains dead organic matter and water; ideal for growing cotton and sugarcane.
3. In India, it is mainly found in Maharashtra, parts of Andhra Padesh, Madhya Pradesh and Gujarat.

Red soils:

1. Red colour is due to the presence of iron oxide.
2. Poor in humas but cannot be made fertile by adding manure or fertilizers.
3. In India, it is found in interior regions of Kerala and Tamil Nadu, Southern Karnataka, Andhra Pradesh, Orissa, Eastern Madhya.

Question 8.
What are the human activities responsible for soil erosion?
Answer:
The various human activities responsible for soil erosion are:

1. Cutting of forests:
With the increase in population and civilisation, deforestation started. Deforestation disturbed the natural habitat of wild animals and at the same time, it enchanced the process of soil erosion.

2. Improper and unscientific methods of agriculture:
Improper and unscientific methods of agriculture also increase the rate of soil erosion.

3. Extensive use of grass lands:
Extensive use of grass lands due to overgrazing by cattle also reduces grass and other, vegetation on the earth which causes erosion of soil.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 8 Winds, Storms and Cyclones

Winds, Storms and Cyclones Intext Questions

Question 1.
I wonder why the winds shown in the figure are not in the exact north – south direction?

Answer:
The winds would have flown in the north – south direction from north to south or from south to north. A change in direction from however, caused by the rotation of the earth.

Question 2.
I want to know what these winds do for us?
Answer:
The winds from the oceans carry water and bring rain. It is a part of the water cycle.

Activities

Activity – 1
Blow the balloons:
Take two balloons of approximately equal size. Put a little water into the balloons. Blow up both the balloons and tie each one to a string. Hang the balloons 8 – 10 cm apart on a cycle spoke or a stick. Blow in the space between the balloons.

Question 1.
What did you expect? What happens?
Answer:
We expected that balloons would move apart. But the balloons come closer.

Activity – 2
Can you blow and lift?
Hold a strip of paper, 20 cm long and 3 cm wide, between your thumb and forefinger as shown in the paper. Paheli Thinks that the strip will be lifted up. Boojho thinks that the strip will bend down.

Question 1.
What do you think Will happen to the paper?
Answer:
Paper strip will be lifted up.

Question 2.
Were the observations along the lines you thought?
Answer:
Yes.

Question 3.
Do you get the feeling that the increased wind speed is accompanied by a reduced air pressure?
Answer:
Yes.

Activity – 3
Take two paper bags or empty paper cups of the same size. Hang the two bags in the inverted position on the two ends of a metal or wooden stick. Tie a piece of thread in the middle of the stick. Hold the stick by the thread (See Fig.) as in a balance. Put a burning candle below one of the bags as shown in the figure. Observe what happens.

Question 1.
Why is the balance of the bags disturbed?
Answer:
The bag below which the candle is lighted, is pushed up by the rising hot air from above the candle flame.

Question 2.
Does this activity indicate that warm air rises up?
Answer:
Yes.

Question 3.
Does the disturbance of the balance suggest that the warm air is lighter than the cold air?
Answer:
Yes.

Winds, Storms and Cyclones Text Book Exercises

Question 1.
Fill the missing word in the blank spaces in the following statements:

1. Wind is ……………. air.
2. Winds are generated due to ……………. heating on the earth.
3. Near the earth’s surface ……………. air rises up whereas air comes down.
4. Air moves from a region of ……………. pressure to a region of pressure.

Answer:

1. Moving
2. Uneven
3. Warm, cooler
4. High, low.

Question 2.
Suggest two methods to find out wind direction at a given place?
Answer:

1. By wind direction indicator.
2. By watching the direction of movement of a paper released in air.

Question 3.
State two experiences that made you think that air exerts pressure (other than those given in the text).
Answer:

1. Compressed air is used in the brake system for stopping trains.
2. Blowing air in a balloon makes it expand.

Question 4.
You want to buy a house. Would you like to buy a house having windows but no ventilators ? Explain your answer.
Answer:
No, a house which has no ventilators is not a healthy house to live in. Basically ventilators provide a path for warm air to go out of the rooms.

Question 5.
Explain why holes are made in hanging banners and hoardings?
Answer:
We know that air exerts pressure, so that due to this pressure banners and hoardings flutter when the wind is blowing. The holes are made in the banners and hoardings as wind pass through that holes and they does not become loose and fall down.

Question 6.
How will you help your neighbours in case cyclone approaches your village/town?
Answer:
I will help by following ways:

1. By warning everyone about the coming danger.
2. Searching for shelter.
3. Moving people fast to safe places.
4. Managing first aid facility.

Question 7.
What planning is required in advance to deal with the situation created by a cyclone?
Answer:
The following planning is required in advance to deal with the situation created by a cyclone:

1. Listening carefully to warnings being transmitted on TV and radio.
2. Setting up cyclone warning system,
3. Moving to cyclone shelter.
4. Storing food in water – proof bags.
5. Keeping an emergency kit ready.

Question 8.
Which one of the following place is unlikely to be affected by a cyclone.

1. Chennai
2. Mangaluru (Mangalore)
3. Amritsar
4. Puri.

Answer:
3. Amritsar.

Question 9.
Which of the statements given below is correct?

1. In winter the winds flow from the land to the ocean.
2. In summer the winds flow from the land towards the ocean.
3. A cyclone is formed by a very high – pressure system with very high – speed winds revolving around it.
4. The coastline of India is not vulnerable to cyclones.

Answer:
1. In winter the winds flow from the land to the ocean.

Extended Learning – Activities and Projects

Question 1.
You can perform the Activity 8.5 (of textbook) in the chapter slight differently at home. Use two plastic bottles of the same size. Stretch one balloon on the neck of each bottle. Keep one bottle in the sun and the other in the shade. Record your observations. Compare these observations and the result with those of Activity 8.5 of text book
Answer:
Do yourself.

Question 2.
You can make your own anemometer?
Answer:
Collect the following items:
4 small paper cups (used ice cream cups), 2 strips of cardboard (20 cm long and 2 cm wide), gum, stapler, a sketch pen and a sharpened pencil with eraser at one end. Take a scale draw crosses on the cardboard strips as shown in the Fig. (a). This will give you the centres of the strips.

Fix the strips at the centre, putting one over the other so that they make a plus (+) sign. Now fix the cups at the ends of the strips. Colour the outer surface of one cup with a marker or a sketch pen. All the 4 cups should face in the same direction.

Push a pin through the centre of the strips and attach the strips and the cups to the eraser of. the pencil. Check that the strips rotate freely when you blow on the cups. Your anemometer is ready. Counting the number of rotations per minute will give you an estimate of the speed of the wind.

To observe the changes in the wind speed, use it at different places and different times of the day. If you do not have a pericil with attached eraser you can use the tip of a ball pen. The only condition is that the strips should rotate freely. Remember that this anemometer will indicate only speed changes. It will not give you the actual wind speed.

Question 3.
Collect articles and photographs from newspapers and magazines about storms and cyclones. Make a story on the basis of what you learnt in this chapter and the matter collected by you?
Answer:
Do with the help of your subject teacher.

Question 4.
Suppose you are a member of a committee, which is responsible for creating development plan of a coastal state. Prepare a short speech indicating the measures to be taken to reduce the suffering of the people caused by cyclones?
Answer:
Do with the help of your subject teacher.

Question 5.
Interview eyewitness to collect the actual experience of people affected by a cyclone?
Answer:
Do with the help of your subject teacher.

Question 6.
Take an aluminium tube about 15 cm long and 1 to 1.5 cm in diameter. Cut slice of a medium – sized potato about 2 cm thick. Insert the tube in the slice, press it, and rotate it 2 – 3 times. Remove the tube. You will find a piece of potato fixed in the tube like a piston head. Repeat the same process with the other end of the tube. Now you have the tube with both ends closed by potato pieces with an air column in between.

Take a pencil with one end unsharpened. Place this end at one of the pieces of potato. Press it suddenly to push the potato piece in the tube. Observe what happens. The activity shows rather dramatically how increased air pressure can push things.
Answer:
Do yourself.

Winds, Storms and Cyclones Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (i)
A storm is marked by –
(a) Strong winds
(b) Rain
(c) Thunder the lightning
(d) All the above.
Answer:
(d) All the above.

Question (ii)
The moving air is called –
(a) Wind
(b) Strong winds
(c) Storm
(d) None of these.
Answer:
(a) Wind

Question (iii)
The amount of water on the earth remains more or less the same because of –
(a) Thunder
(b) Storm
(c) Flood
(d) Water cycle.
Answer:
(d) Water cycle.

Question (iv)
The word monsoon is derived from –
(a) Arabic word
(b) English word
(c) Hindi word
(d) Urdu word.
Answer:
(a) Arabic word

Question (v)
The diameter of the eye of the cyclone varies from –
(a) 10 km to 15 km
(b) 10 km to 20 km
(c) 10 km to 30 km
(d) 10 km to 40 km.
Answer:
(c) 10 km to 30 km

Question (vi)
A violent tornado can travel at speeds of about –
(a) 200 km/h
(b) 300 km/h
(c) 350 km/h
(d) None of these.
Answer:
(b) 300 km/h

Question 2.
Fill in the blanks :

1. Orissa was hit by a cyclone with wind speed of 200 km/h on …………….
2. On 29 October, 1999, a second cyclone with wind speed of ……………. hit Orissa again.
3. The greater the difference in pressure, the ……………. the air moves.
4. The worm air is lighter than the ……………. air.
5. At the poles, the air is colder than that at latitudes about ……………. degrees.
6. The word monsoon is derived from the Arabic word …………….
7. Clouds bring ……………..
8. Farmers in our country depend mainly on rains for their …………….
9. A large cyclone is a violently rotating mass of ………… in the atmosphere.
10. A tornado is a ……………. funnel shaped cloud that reaches from the sky to the ground.

Answer:

1. 18 October 1999
2. 260 km/h
3. Faster
4. Cold,
5. 60
6. Mausam
7. Rain
8. Harvests
9. Air
10. Dark.

Question 3.
Which of the following statements are true (T) or false (F):

1. The cyclone affected agriculture, communication, transport and electricity supply.
2. On heating the air expands and occupies more space
3. In winter, the direction of the wind flow gets reversed.
4. The winds from the oceans carry water arid bring rain.
5. Water cycle is not a continuous phenomenon.
6. Thunderstorms are caused by violent air current inside the cumulus clouds.
7. The cyclones are called hurricane in America.
8. The storms are called typhoons in China.
9. Uneven heating on the earth is the main cause of wind movement.
10. We must stand under a high-rise building or a tree when caught in a thunderstorm.
11. Tropical cyclones occur throughout the year.
12. Lightning, rains and storms are always harmful for the earth.

Answer:

1. True (T)
2. True (T)
3. True (T)
4. True (T)
5. False (F)
6. True (T)
7. True (T)
8. True (T)
9. True (T)
10. False (F)
11. False (F)
12. False (F)

Question 4.
Match the items in Column A with Column B:

Answer:

(i) (b)
(ii) (c)
(iii) (d)
(iv) (a).

Winds, Storms and Cyclones Very Short Answer Type Questions

Question 1.
What is a wind?
Answer:
The moving air is called wind.

Question 2.
Define the term cycle?
Answer:
A cycle is an event or phenomenon which repeats it selfs after sometime.

Question 3.
Define the term evaporation?
Answer:
The process of changing water from its liquid form to its vapour is known as evaporation.

Question 4.
When you fly a kite, does the wind coming from your back help?
Answer:
Yes.

Question 5.
If you are in a boat, is it easier to row it if there is wind coming from behind you?
Answer:
Yes.

Question 6.
Define tornadoes?
Answer:
A tornado is a dark funnel shaped cloud that reaches from the sky to the ground. In our country tornadoes are not very frequent.

Question 7.
Which region gets maximum sunlight?
Answer:
Regions close to the equator get maximum sunlight.

Question 8.
What do you mean by the “eye” of a storm?
Answer:
The centre of a cyclone is calm area. It is called the eye of the storm.

Question 9.
Can you imagine what would happen if high speed winds blow over the roofs of buildings?
Answer:
If the roofs were weak, they would be lifted and blown away.

Question 10.
What do you mean by “hurricane”?
Answer:
“Hurricane” is the term used for storm in West Indies and America.

Question 11.
When is cyclone alert issued?
Answer:
A cyclone alert or cyclone watch is issued 48 hours in advance of any expected storm.

Question 12.
Which factors contribute to the development of cyclone?
Answer:
Facters like wind speed, wind direction, humidity and temperature contribute to the development of cyclones.

Question 13.
When is cyclone warning issued?
Answer:
A cyclone warning is issued 24 hours in advance.

Question 14.
Why smoke always rises up?
Answer:
Smoke is hotter than air, so it is also lighter than air. That is why smoke always moves up.

Question 5.
How do “high – speed winds” harm us ?
Answer:
High – speed winds accompanying a cyclone can damage houses, telephones and other communication systems, trees, etc. causing tremendous loss of life and property.

Question 16.
What is “beaufort scale”?
Answer:
The number and name of a wind is determined by the speed at which it flows on an internationally accepted scale, called beaufort scale.

Question 17.
Is our body a conductor?
Answer:
Yes.

Question 18.
How are high building protected from lightning?
Answer:
High buildings are protected from lightning by fixing lightning conductor on the building.

Winds, Storms and Cyclones Short Answer Type Questions

Question 1.
How is storm caused?
Answer:
When the wind blows gently, it is called a breeze. But, when it blows very fast it cause storm. Storm may be defined as something taking place in the weather of a violent nature. At sea, a storm may be a strong wind or gale. On land, a storm usually means a weather situation marked by heavy rain and often with strong winds, lightning and thunder.

Question 2.
Explain the structure of a tornado?
Answer:
The diameter of a tornado can be as small as a metre and as large as a kilometer, or even wider. The funnel of a tornado sucks dust, debris and everything near it at the base (due to low pressure) and throws out near the top.

Question 3.
How is lightning useful in nature?
Answer:
Lightning is useful in nature because during lightning in tense heat and high temperature are produced. As a result, nitrogen combines with oxygen to form its oxides. These oxides of nitrogen further get dissolved in water to form a dilute solution of nitric acid that comes to the ground with rain. This is how nature provides nitrogenous compounds to plants that are important for their growth.

Question 4.
How are lightning and thunder caused?
Answer:
When two oppositily charged clouds are near each other, the air between them becomes good conductor because charges begin, to move in air very speedily. The presence of electric charges in very large quantities in the air causes to appear as sleaks of lightning and thunder.

Question 5.
Explain the terms thunderstorms and cyclones.
Answer:
Thunderstorms develop in hot, humid tropical areas like India very frequently. The rising temperatures produce strong upward rising winds. These winds carry water droplets upwards, where they freeze, and fall down again. The swift movement of the falling waterd roplets along with the rising air create lightning and sound. It is this event that we call a thunderstorm.

Question 6.
Suggest precautios if a storm is accompanied by lightning?
Answer:
If a storm is accompanied by lightning, we must take the following precautions:

1. Do not take shelter under an isolated tree. If you are in a forest take shelter under a small tree. Do not lie on the ground,
2. Do not take shelter under an umbrella with a metallic end.
3. Do not sit near a window. Open garages, storage sheds, metal sheds are not safe places to take shelter.
4. A car or a bus is a safe place to take shelter.
5. If you are in water, get out and go inside a building.

Question 7.
Suggest some effective safety measures for cyclone.
Answer:
Some Effective Safety Measures:

1. A cyclone forecast and warning service.
2. Rapid communication of. warnings to the Government agencies, the ports, fishermen, ships and to the general public.
3. Construction of cyclone shelters in the cyclone prone areas, and Administrative arrangements for moving people fast to safer places.

Winds, Storms and Cyclones Long Answer Type Questions

Question 1.
How does a thunderstorm becomes a cyclone?
Answer:
Before cloud formation, water takes up heat from the atmosphere to change into vapour. When water vapour changes back to liquid form as raindrops, this heat is released to the atmosphere. The heat released to the atmosphere warms the air around. The air tends to rise and causes a drop in pressure. More air rushes to the centre of the storm. This cycle is repeated. The chain of events ends with the formation of a very low – pressure system with very high – speed winds revolving around it. It is this weather condition that we call a cyclone. Factors like wind speed, wind direction, temperature and humidity contribute to the development of cyclones.

Question 2.
Define the structure of a cyclone?
Answer:
Structure of a cyclone:
The centre of a cyclone is a calm area. It is called the eye of the storm. A large cyclone is a violently rotating mass of air in the atmosphere, 10 to 15 km high. The diameter of the eye varies from 10 to 30 km. It is a region free of clouds and has light winds. Around this calm and clear eye (See Fig.), there is a cloud region of about 150 km in size.

In this region there are high – speed winds (150-250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases. The formation of a cyclone is a very complex process.

Question 3.
With a neat diagram show the formation of a cyclone.
Answer:

Question 4.
Describe the action taken by the people and some precautions if you are staying in a cyclone hit area?
Answer:
Action on the part of the people:

1. We should not ignore the warnings issued by the meteorological department throught TV, radio, or newspapers.
2. We should make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places.
3. We should avoid driving on roads through standing water, as floods may have damaged the roads.
4. We should keep ready the phone numbers of all emergency sendees like police, fire brigade, and medical centres.

Some precautions, if you are staying in a cyclone hit area:

1. Do not drink water that could be contaminted. Always store drinking water for emergencies.
2. Do not touch wet switches and fallen power lines.
3. Do not go out just for the sake of fun.
4. Do not pressurise the rescue force by making undue demands.
5. Cooperate and help your neighbours and friends

Question 5.
Show the phenomena that lead to the formation of clouds and falling of rain and creation of storms and cyclones with the help of a flow diagram or a flow chart.
Answer:

Question 6.
On a map, show the regions near the equator where cyclones form.
Answer:

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 7 Weather, Climate and Adaptations of Animals of Climate

Weather Climate and Adaptations of Animals of Climate  Intext Questions

Question 1.
I wonder who prepares the wheather report?
Answer:
The weather reports are prepared by the Meteorological Department of the Government.

Question 2.
I wonder why weather changes so frequently?
Answer:
Because factors affecting weather like temperature, humidity, etc. vary frequently.

Question 3.
What is the source of whether in the first place?
Answer:
All changes in the weather are caused due to sun.

Question 4.
Do fishes and butterflies also migrate like birds?
Answer:
No.

Activity
Fill all the columns according to the data in the chart that you have prepared.
Answer:
Table
Weather data of a week

(Rainfall may not be recorded for all the days since it may not rain everyday.)

Weather, Climate and Adaptations of Animals of Climate Text Book Exercises

Question 1.
Name the elements that determine the weather of a place?
Answer:
The day – to – day condition of the atmosphere at a place with respect to the temperature, rainfall, humidity, wind – speed, etc., is called the weather at that place.

Question 2.
When are the maximum and minimum temperature likely to occur during the day?
Answer:
The maximum temperature of the day occurs generally in the afternoon while the minimum temperature occurs in the early morning.

Question 3.
Fill in the blanks:

1. The average weather taken over a long time is called …………..
2. A place receives very little rainfall and the temperature is high throughout the year, the climate of that place will be ……………. and
3. The two regions of the earth with extreme climatic conditions are ………….. and ……………

Answer:

1. Climate of the place
2. Hot, dry
3. Tropical, polar regions.

Question 4.
Indicate the type of climate of the following areas:

1. Jammu and Kashmir –
2. Kerala –
3. Rajasthan –
4. North – east India –

Answer:

1. Moderately hot and moderately wet climate.
2. Very hot and wet climate.
3. Hot and dry climate.
4. Wet climate.

Question 5.
Which of the two changes frequently weather or climate?
Answer:
Weather.

Question 6.
Following are some of the characteristics of animals:

1. Diets heavy on fruits
2. White fur
3. Need to migrate
4. Loud voice
5. Sticky pads on feet
6. Layer of fat under skin
7. Wide and large paws
8. Bright colours
9. Strong tails
10. Long and Large beak.

For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do you think that some of there characteristics can be adapted for both regions?
Answer:

1. Tropical rainforests
2. Polar region
3. Polar region
4. Tropical rainforesl
5. Tropical rainforests
6. Polar region
7. Polar region
8. Tropical rainforets
9. Tropical rain.forests
10. Tropical rainfore’t

Question 7.
The tropical rainforest has a large population of animals. Explain why it is so?
Answer:
Tropical rain are found in Western Ghats and Assam in India, South – east Asia, central America and Central Africa. Because of continuous warmth and rain, this region supports wide variety of plants and animals. The major types of animals living in the rainforests are apes, gorillas, monkeys, tigers, lions, leopards, lizards, elephants, insects, birds and snakes.

The climate conditions in rainforests are highly suitable for supporting an enormous number and variety of animals. Thus, we can say that because of the hospitable climate conditions huge populations of plants and animals are found in the tropical rainforests.

Question 8.
Explain, with examples, why we find animals of certain kind living in particular climatic conditions?
Answer:
Animals are adapted to survive in the conditions in which they live. Animals living in very cold and hot climate must possess special features to protect themselves against the extreme cold or heat. Polar bears have white fur so that they are not easily visible in the snowy white background. It protects them from their predators. It also helps them in catching their prey. To protect them from extreme cold, they have two thick layers of fur.

They also have a layer of fat under their skin. In fact, they are so well – insulated that they have to move slowly and rest often to avoid getting overheated. Physical activities on warm days necessitate cooling. So, the polar bear goes for swimming. It is a good swimmer. Its paws are wide and large, which help it not only to swim well but also walk with ease in the snow. While swimming under water, it can close its nostrils and can remain under water for long durations.

It has a strong sense of smell so that it can catch its prey for food. Another well – known animal living in the polar regions is the penguin (Fig.). It is also white and merges well wTith the white background. It also has a thick skin and a lot of fat to protect it from cold. You may have seen pictures of penguins huddled together. This they do to keep warm.

Question 9.
How do elephant living in the tropical rainforest adapt itself?
Answer:
The elephant has adapted to the conditions of rainforests in many remarkable ways. Look at its trunk. It uses it as a nose because of whjch it has a strong sense of smell. The trunk is also used by it for picking up food. Moreover, its tusks are modified teeth. These can tear the bark of trees that elephant loves to eat.

So, the elephant is able to handle the competition for food rather well. Large ears of the elephant help it to hear even very soft sounds. They also help the elephant to 4 keep cool in the hot and humid climate of the rainforest.

Choose the correct option which answers the following question:

Question 10.
A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in

1. Polar regions
2. Deserts
3. Oceans
4. Tropical rainforests.

Answer:
4. Tropical rainforests.

Question 11.
Which features adapt polar bears to live in extremely cold climate?

1. A white fur, fat below skin, keen sense of smell.
2. Thin skin, large eyes, a white fur.
3. A long tail, strong claws, white large paws.
4. White body, paws for swimming, gills for respiration.

Answer:
1. A white fur, fat below skin, keen sense of smell.

Question 12.
Which option best describes a tropical region?

1. Hot and humid
2. Moderate temperature, heavy rainfall
3. Cold and humid
4. Hot and dry.

Answer:
1. Hot and humid.

Extended Learning – Projects and Activities

Question 1.
Collect weather reports of seven successive days in the winter months (preferably December). Collect similar reports for the summer months (preferably June). Now prepare a table for sunrise and sunset times as shown:
Table

Try to answer the following questions:

1. Is there any difference in the time of sunrise during summer and winter?
2. When do you find that the sun rises earlier?
3. Do you also find any difference in the time of sunset during the month of June and December?
4. When are the days longer?
5. When are the nights longer?
6. Why are the days sometimes longer and sometimes shorter?
7. Plot the length of the days against the days chosen in June and December?

Answer:

1. Yes.
2. Sunrises earlier during summer.
3. Yes, sunsets earlier during winter.
4. During summer, the days are longer.
5. During winter, the nights are longer.
6. Earth revolves around the sun. During different times, the angle of earth with the sun changes. This causes the difference in length of day and night.
7. Length.

Question 2.
Collect information about the Indian Meteorological Department. If possible visit its website: http//www.imd.gov.in. Write a brief report about the things this department does.
Answer:
Do with the help of your subject teacher.

Weather, Climate and Adaptations of Animals of Climate Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (i)
The weather reports are prepared by the –
(a) Meteorological Department of the Government
(b) Agricultural Department of the Government
(c) Radio and TV Department of the Government
(d) None of these.
Answer:
(a) Meteorological Department of the Government

Question (ii)
The climate of the north – east is –
(a) Hot
(b) Wet
(c) Cold
(d) Dry.
Answer:
(b) Wet

Question (iii)
The climate of the western region is –
(a) Hot
(b) Wet
(c) Dry
(d) Hot and dry.
Answer:
(d) Hot and dry.

Question (iv)
The lion – tailed macaque lives in the rainforests of –
(a) Western Ghats
(b) Eastern Ghats
(c) Both (a) and (b)
(d) None of these.
Answer:
(a) Western Ghats

Question (v)
Which are of the following is a migratory bird –
(a) Penguin
(b) Peacock
(c) Crow
(d) Siberian crane.
Answer:
(d) Siberian crane.

Question 2.
Fill in the blanks:

1. The temperature, humidity and other factors are called the ……………. of the weather.
2. Rainfall is measured by an instrument called the …………….
3. All changes in the weather are caused by …………….
4.  ……………. Record the weather every day.
5. The polar regions are situated near the …………….
6. Musk oxen, foxes, seals, etc. are living in the ……………. regions.
7. The tropical region has generally a ……………. climate.
8. Animals are adapted to the conditions in which they …………….
9. Penguins lives in ……………. regions.
10. The beard ape lives in the rainforests of …………….

Answer:

1. Elements
2. Rain gauge
3. Sun
4. Meteorologists
5. Poles
6. Polar
7. Hot
8. Live
9. Very cold
10. Western Ghats.

Question 3.
Which of the following statements are true (T) or false (F):

1. The weather is generally not the same on any two days and week after week.
2. The camel is called the ship of the desert.
3. The times of sunrise and sunset also change during the year.
4. The climate of the Kerala is very cold for most part of the year
5. Penguins lives in very cold.
6. Animals are adapted to the conditions in which they live.
7. All the changes in the weather are driven by the sun.
8. Migration is another means to escape the harsh, cold conditions.
9. Polar bears are found in Indian tropical rainforests.
10. The winter sleep of animals is called migration.

Answer:

1. True (T)
2. True (T)
3. True (T)
4. False (F)
5. True (T)
6. True (T)
7. True (T)
8. True (T)
9. False (F)
10. False (F).

Question 4.
Match the items in Column A with Column B:

Answer:

(i) (b)
(ii) (d)
(iii) (a)
(iv) (c)

Weather, Climate and Adaptations of Animals of Climate vert short  Answer Type Questions

Question 1.
Who prepares the weather report?
Answer:
The weather reports are prepared by the Metreological Department of the Government.

Question 2.
What do you mean by weather?
Answer:
The day – to – day condition of the atmosphere at a place with respect to the temperature, rainfall, wind speed, humidity, is called the weather of that place.

Question 3.
What do you mean by climate?
Answer:
The average weather pattern taken over a long time, say 25 years, is called the climate of the place.

Question 4.
When is the climate of a place called hot and wet?
Answer:
If there is heavy rainfall on most of the days as well as the temperature is high in the same place, then we can say that the climate of that place is hot and wet.

Question 5.
When is the climate of a place called hot?
Answer:
If the temperature at a place is high most of the time, then we say that the climate of that place is hot.

Question 6.
Why do some places have hotter climate than others?
Answer:
The places nearer to the equator are usually hotter. This is because the sim’s rays are more concentrated near the equator than they are farther North or South.

Question 7.
Which causes the changes in weather?
Answer:
Sun.

Question 8.
Name the location in India where climate is hot and dry?
Answer:
Rajasthan.

Question 9.
Name the location in India where climate is wet.
Answer:
North – east.

Question 10.
Define raingauge.
Answer:
Rainfall is measured by an instrument called the raingauge.

Question 11.
Name two animals found in cold climate?
Answer:
Polar bear and Penguins.

Question 12.
Name two animals found in hot and humid climate.
Answer:
Beard ape and Red – eyed frog.

Question 13.
Name two deserts animal.
Answer:
Camel and snake.

Question 14.
Where does penguin live?
Answer:
Penguin lives in very cold places.

Question 15.
What makes penguins good swimmers?
Answer:
Penguin’s bodies are streamlined and their feet have webs, making them good swimmers.

Question 16.
How are the paws of a polar bear?
Answer:
Wide and large.

Question 17.
Can a polar bear live happily on land?
Answer:
No, it lives happily where the land is fully covered with snow.

Question 18.
Where do the elephant live ?
Answer:
Elephant lives in forest.

Question 19.
Name two countries where the tropical rainforests are found?
Answer:
India and Brazil.

Question 20.
Name two countries where polar regions are found?
Answer:
Sweden and Canada.

Question 21.
Name four countries in polar region?
Answer:
Norway, Iceland, Canada and Greenland.

Question 22.
Name the major types of animals living in rainforest?
Answer:
The major types of animals living in the rainforests are apes, lions, tigers, monkeys, gorillas, elephants, leopards, snakes, birds and lizards.

Question 23.
Where do the following animals live?

1. Fish
2. Monkeys
3. Snakes

Answer:

1. In water
2. On land and trees
3. On land and water.

Question 24.
Name any two animals which are active during night?
Answer:
Owl and Bat.

Question 25.
Name the bird from Siberia that comes to India?
Answer:
Siberian Crane.

Weather, Climate and Adaptations of Animals of Climate Short Answer Type Questions

Question 1.
Differentiate between weather and climate?
Answer:
Difference between weather and climate:

Weather:
The day – to – day condition of the atmosphere at a place with respect to the temperature, rainfall, windspeed, humidity, etc. is called the weather at that place.

Climate:
The average weather pattern taken over a long time, say 25 years, is called the climate of that place.

Question 2.
Write a short note on the sun?
Answer:
All changes in the weather are caused by the sun. The sun is a huge sphere of hot gases at a very high temperature. The distance of the sun from us is very large. Even then the energy sent out by the sun is so huge that it is the source of all heat and light on the earth. So, the sun is the primary source of energy that causes changes in the weather.

Energy absorbed and reflected by the earth’s surface, oceans and the atmosphere play important roles in determining the weather at any place. If you live near the sea, you would have realised that the weather at your place is different from that of a place in a desert, or near a mountain.

Question 3.
How do penguins adapt with polar climate?
Answer: Penguins are white and merge well with the white background. They also have a thick skin and a lot of fat to protect it from cold. Penguins huddle together. This they do to keep warm. Further, their bodies are streamlined and their feet have webs, making them good swimmers.

Question 4.
How is camel adapted to live in desert?
Answer:
Camel lives in desert. It has long legs which help it to lift its body above the ground. So, camel is able to avoid direct contact with the hot ground. Camel drinks more than 50 litres of water at a time. Camel store the water in his body. So that it lives without water for a longer time. Due to its thick skin, transpiration of water is also prevents. That’s why camel is suited to live in desert.

Question 5.
How are fishes adapted to live in water?
Answer:
Fishes are best suited to live in water. They have structure like a boat, which help them in swimming in water. They have gills from which they get food and oxygen. The body of fishes contain different types of fins which help them for swimming in water.

Question 6.
What is the climate of polar regions?
Answer:
The polar regions present an extreme climate. These regions are covered with snow and it is very cold for most part of the year. For six months the sun does not set at the poles while for the other six months the sun does not rise. In winters, the temperature can be as low as _–37°C. Animals living there have adapted to these severe conditions.

Question 7.
Where the polar regions are situated? Name some of the countries that belong to the polar regions. Also name the some countries where the tropical rainforests are found.
Answer:
The polar regions are situated near the poles, i.e., north pole and south pole. Some well – known countries that belong to the polar regions are Canada, Greenland, Iceland, Norway, Sweden, Finland, Alaska in U.S.A. and Siberian region of Russia. Some countries where the tropical rainforests are found are India, Malaysia, Indonesia, Brazil, Republic of Congo, Kenya, Uganda, and Nigeria.

Question 8.
Write the features of lion – tailed macaque?
Answer:
The lion – tailed macaque (also called Beard ape) lives in the rainforests of Western Ghats. Its most outstanding feature is the silver – white mane, which surrounds the head from the cheeks down to its chin. It is a good climber and spends a major part of its life on the tree. It feeds mainly on fruits. It also eats seeds, young leaves, stems, flowers and buds. This beard ape also searches for insects under the bark of the trees. Since it is able to get sufficient food on the trees, it rarely comes down on the ground.

Weather, Climate and Adaptations of Animals of Climate Long Answer Type Questions

Question 1.
Answer:

Question 2.
Write a note about “climate of the tropical rainforests”?
Answer:
The tropical region has generally a hot climate because of its location around the equator. Even in the coldest month the temperature is generally higher than about 15°C. During hot summers, the temperature may cross 40°C. Days and nights are almost equal in length throughout the year. These regions get plenty of rainfall. An important feature of this region is the tropical rainforests. Tropical rainforests are found in Western Ghats and Assam in India, Southeast Asia, Central America and Central Africa. Because of continuous warmth and rain, this region supports wide variety of plants and animals. The major types of animals living in the rainforests are monkeys, apes, gorillas, lions, tigers, elephants, leopards, lizards, snakes, birds and insects.

Question 3.
For which animals the climatic conditions in rainforests are highly suitable?
Answer:
The climatic conditions in rainforests are highly suitable for supporting an enormous number and variety of animals. Since the numbers are large, there is intense competition for food and shelter. Many animals are adapted to living on the trees. Red – eyed frog (Fig. (a)) has developed sticky pads on its feet to help it climb trees on which it lives. To help them live on the trees, monkeys (Fig. (b)) have long tails for grasping branches. Their hands and feet are such that they can easily hold on to the branches.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 6 Physical and Chemical Changes

Activities

Activity 1
Make a list of eight changes you have noticed from your surroundings.
Answer:
The changes are as:

1. Motion of fan
2. Lighting of a tubelight
3. Vaporisation of water
4. Melting of ice
5. Sound produced by radio
6. Blooming of flower
7. Changing of day and night
8. Changing of the shape of sun.

Activity 2
Try to indentify changes that you observe around you as physical or chemical changes.
Answer:

Physical and Chemical Changes Text book Exercises

Question 1.
Classify the changes involved in the following processes as physical or chemical changes?

1. Photosynthesis
2. Dissolving sugar in water
3. Burning of coal
4. Melting of wax
5. Beating aluminium to make aluminium foil
6. Digestion of food

Answer:

1. Chemical change
2. Physical change
3. Chemical change
4. Physical change
5. Physical change
6. Chemical change.

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in you notebook?

1. Cutting a log food into pieces is a chemical change. (T/F)
2. Formation are from leaves is a physical change. (T/F)
3. Iron pipes coated with zinc do not get rusted easily. (T/F)
4. Iron and rust are the same substances. (T/F)
5. Condensation of steam is not a chemical change. (T/F)

Answer:

1. False (F)
2. False (F)
3. True (T)
4. True (T)
5. True (T)

Question 3.
Fill in the blanks in the following statements:

1. When carbon dioxide is passed through lime water, it turns milky due to the formation of ……………
2. The chemical name of baking soda is ……………
3. Two methods by which rusting of iron can be prevented are …………… and ……………
4. Changes in which only …………… properties of a substance change are called physical changes.
5. Changes in which new substances are formed are called …………… changes.

Answer:

1. calcium carbonate
2. Sodium hydrogen carbonate
3. coating, galvanization
4. physical
5. chemical

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of changes is it? Explain.
Answer:
It is a chemical change. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas carbaon – dioxide.
Lemon juice + Baking soda Carbon dioxide + Lime water.

Question 5.
When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place?
Answer:
Melting of wax is a physical change while burning of candle is a chemical change. Lightning torch bulb using dry cell is another example where both physical and chemical changes takes place. The lighting of the bulb is physical change while current from the dry cell is obtained by the chemical substances inside it.

This is chemical change because the chemicals in the cell get converted into new substances and hence the cell ultimately becomes useless.

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The conversion of milk into curd, i.e., setting of curd is a permanent as well as irreversible and lead to the production of a new substance. The curd is not be converted into milk. Thus, the formation of curd is a chemical change.

Question 7.
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Answer:
Burning of a wood is a chemical change because in addition to new products burning is always accompanied by production of heat. Cutting of wood into small pieces is a physical change because pieces of wood under went changes in size and no new substances is formed.

Question 8.
Describe how crystals of copper sulphate are prepared?
Answer:
Take a cupful of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuiously (fig.). Continue adding copper sulphate powder, till no more powder can be dissolved. Filter the solution. Allow it to cool.

Do not disturb the solution when it is cooling. Look at the solution after some time. Can you see the crystals of copper sulphate? If not, wait for some more time. Crystals of copper sulphate slowly from at the bottom of the beaker.

Question 9.
Explain how painting of an iron gate prevents it from rusting?
Answer:
For rusting, iron must be in contact with both air and moisture. When iron gate is painteel the layer of paint cuts the contact between air, moisture and iron. Thus, it prevents rusting.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts?
Answer:
The water of coastal areas containing many salts. The salt water makes the process of rust formation faster. Thus, rusting of iron objects is faster in coastal areas than deserts.

Question 11.
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change A) then it burns (Change B). The following statements pertain to these changes. Choose the correct one.

1. Process – A is a chemical change.
2. Process – B is a chemical change.
3. Both processes – A and B are chemical changes.
4. None of these processes is a chemical change.

Answer:
3. Both processes – A and B are chemical changes.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change A). The biogas is then burnt as fuel (Change B). The following statements pertain to these changes. Choose the correct one.

1. Process – A is a chemical change.
2. Process – B is a chemical change.
3. Both processes – A and B are chemical changes.
4. None of these processes is a chemical change.

Answer:
3. Both processes – A and B are chemical changes.

Extended Learning – Activities and Projects

Question 1.
Describe two changes that are harmful. Explain why you consider them harmful. How can you prevent them?
Answer:
1. Spoilage of Food:
Food items when kept carelessly, get spoiled. This is a chemical change and obviously harmful for our health. Basically, the food is spoiled by microorganisms.

Preventation of Food Spoilage:
Microorganisms do not survive high or low temperature. So, food items stored in refrigerator do not spoil. Also, we should keep them covered, so that microorganism do not get any change to spoil them.

2. Rusting:
If a piece of iron is left in open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting.

Iron benches kept in parks, gardens and lawns, iron gates of parks, farm houses, houses; almost every article of iron, kept in open gets rusted.

The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂, from the air) + water (H₂O) → Rust (ironoxide, Fe₂O₃)
For rusting, the presence of both water (or water vapour) and oxygen is essential. Rusting is harmful because, it destorys the iron objects. Iron is the most widely used metal and so rusting is a serious problem.

Preventation of rusting:
It can be prevented by preventing iron things from coming in contact with water, oxygen, or both. One simple way is to apply a coat of paint or grease. In fact, these coats should be applied regularly to prevent rusting.

Another way is to deposit a layer of a metal like chromium or zinc on iron. This process is called galvanisation. Generally the iron pipes, which are used in our homes for water supply are galvanised to prevent rusting.

Question 2.
Take three glass bottles with wide mouths. Label them, A, B and C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil to the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations?
Answer:
The nails in bottle B rust a little, nails in bottle A are the most rusted and that is bottle C remain unchanged. For rusting both oxygen and water are necessary. Both of these factors are present in the bottle A, since oxygen is dissolved in water. In bottle B, water is boiled and hence dissolved air is removed. Due to lack of oxygen, iron nail does not rust much. In bottle C, the layer of oil present dissolution of air in the water and hence no rusting occurs.

Question 3.
Prepare crystals of alum.
Answer:
Take a cupful of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuiously (fig.). Continue adding copper sulphate powder, till no more powder can be dissolved. Filter the solution. Allow it to cool.

Do not disturb the solution when it is cooling. Look at the solution after some time. Can you see the crystals of copper sulphate? If not, wait for some more time. Crystals of copper sulphate slowly from at the bottom of the beaker.

Question 4.
Collect information about the types of fuels used for cooking in you area. Discuss with your teachers/ parents/ others which fuels are less polluting and why?
Answer:
The different fuels used for cooking are wood, cow – dung cake, kerosene, biogas and LPG. Among all of these, biogas and LPG are least polluting. Both of these burn completely and do not give smoke. Also there is no residue i.e. ash after burning. Thus, these fuels are less polluting.

Physical and Chemical Changes Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative

Question (i)
Which of the following is not a chemical change –
(a) Digestion of food
(t) Burning of oaal
(c) Curdling of milk
(d) Melting Of ice.
Answer:
(d) Melting Of ice.

Question (ii)
Properties such as shape, size, colour and state of a sub-stance are called its –
(a) Chemical properties
(b) Physical properties
(c) Both (a) and (b)
(d) None of these.
Answer:
(b) Physical properties

Question (iii)
The substances formed as a result of chemical reaction are called –
(a) Materials
(b) Products
(c) Reactants
(d) ingredients.
Answer:
(b) Products

Question (iv)
Rusting of iron is a
(a) Slow reaction
(b) Fast reaction
(c) Both (a) and (b)
(d) None of these.
Answer:
(a) Slow reaction

Question (v)
Qutub minar was built more than years ago –
(a) 1600
(b) 1650
(c) 1700
(d) 1800.
Answer:
(a) 1600

Question 2.
Fill in the blanks:

1. A physical change is generally ……………..
2. A chemical change is also called a …………….. reaction.
3. Chemical changes are very important in our ……………..
4. Ozone layer protects us from the harmful …………….. radiation which come from the sun.
5. Oxygen is …………….. from ozone.
6. If the content of moisture in air is high, which means if it is more humid, rusting becomes ……………..
7. The process of depositing a layer of zinc on iron is called ……………..
8. Stainless steel does …………….. rust.
9. In chemical changes …………….. substances are produced.
10. Burning of coal, wood or leaves is a …………….. change.

Answer:

1. Reversible
2. Chemical
3. Lives
4. Ultraviolet
5. Different
6. Faster
7. Galvanisation
8. Hot
9. New
10. Chemical.

Question 3.
Which of the following statements are true (T) or false (F):

1. Conversion of milk into curd is a physical change.
2. A physical change is generally reversible.
3. On dissolving the ash in water it forms a new substance.
4. When carbon dioxide is passed throuth lime water, calcium carbonate is formed, which makes lime water milky.
5. Chemical changes are not important in our lives.
6. All new substances are formed as a result of chemical changes.
7. A medicine is the end product of a chain of chemical reactions.
8. Stainless steel is made by mixing iron with carbon and metals.

Answer:

1. False (F)
2. True (T)
3. True (T)
4. True (T)
5. False (F)
6. True (T)
7. True (T)
8. True (T).

Question 4.
Match the items in Column A with Column B:

Answer:

(i) (b)
(ii) (d)
(iii) (a)
(iv) (c)

Physical and Chemical Changes Very Short  Answer Type Question

Question 1.
Define a physical change.
Answer:
The change in which the identity of the substance does not change is called a physical change.

Question 2.
Give any one characteristic of a physical change.
Answer:
No new substance is formed as a result of physical change.

Question 3.
List two physical changes.
Answer:

1. Change of an iron bar to a magnet.
2. Melting of ice.

Question 4.
Complete the following:

1. In a physical change the state of the substance is ………….. if cause of the change is removed.
2. In a physical change only ……………… physical properties of the substance are

Answer:

1. Restored
2. Changed.

Question 5.
Define a chemical change.
Answer:
It is the change in which identity of the substance is changed and a new substance is formed-

Question 6.
Which of the following is true in case of a chemical change:

1. Identity of the substance does not change.
2. No, new substance is formed.
3. Only physical properties of the substance are changed.
4. Chemical properties of the substance are changed.

Answer:
4. Chemical properties of the substance are changed.

Question 7.
Give any one important characteristic of a chemical change?
Answer:
In this change new substance is formed.

Question 8.
Give any two examples of a physical change?
Answer:

1. Dissolution of common salt (or sugar) in water.
2. Magnetisation of an iron piece and demagnetisation of a magnet.

Question 9.
Is glowing of an electric bulb is a physical change or chemical ?
Answer:
Physical change.

Question 10.
List any two chemical changes with which we come across in our daily life.
Answer:

1. Durdling of milk, and
2. Digestion of food.

Question 11.
Classify the following into physical change and chemical change:

(a) Souring of kneaded flour
(b) Change of sugarcane juice to vinegar
(c) Evaporation of water
(d) Change of an iron rod to a magnet
(e) Pickling
(f) Dissolving common salt in water
(g) Change of cattle dung to biogas
(h) Glowing of an electric bulb.

Answer:

Physical change: (c), (d), (f), (h).
Chemical change: (a), (b), (e), (g).

Question 12.
Give one difference between physical and chemical change.
Answer:
In a physical change new substance is not formed, whereas in a chemical change new substance is formed.

Question 13.
Are the following changes physical or chemical:

1. Burning of candle
2. Preparation of soap from oil and caustic soda
3. Dissolving sugar in cone, sulphuric acid, and
4. conversion of grape juice to wine.

Answer:
Chemical change.

Question 14.
Pick up chemical changes out of the following:

(a) Souring of milk
(b) Making of ice – cream
(c) Burning of a candle
(d) Lighting of an electric bulb
(e) Respiration
(f) Heating of ammonium chloride
(g) Melting of wax.
(h) Breaking a chalk.

Answer:

Physical change: (b), (d), (f), (g), (h).
Chemical change: (a), (c), (e).

Question 15.
What are main points under which physical changes can be classified?
Answer:
The three main points viz. change in state, dispersion in solution, magnetisation and electrical changes.

Question 16.
Define rate of a chemical reaction.
Answer:
The rate of reaction is the quantity of products obtained per unit time from the reactant.

Question 17.
List a fast reaction.
Answer:
2Na + 2H₂O → 2NaOH + H₂ ↑

Question 18.
List the factors which influence the rate of a chemical reaction.
Answer:

1. Nature and state of reactants
2. Temperature
3. Concentration of the reactants
4. Catalyst.

Question 19.
What happens when temperature of a chemical reaction increases?
Answer:
Rate of reaction increases.

Physical and Chemical Changes Short Answer Type Question

Question 1.
How can you say that burning of coal and passing of electric current through water are chemical changes?
Answer:
Burning of coal:
When coal is burnt carbon dioxide gas is formed and ash is left behind as residue. Thus, new substances with new properties are formed. It is because the molecular structure of carbon-dioxide and coal are quite different from that of coal. Further more coal cannot be obtained back, hence it is a permanent change. So, it is a chemical change.

Passing of electric currnet through water:
When electric current is passed throuth water it decomposes to hydrogen and oxygen. The molecular structure of the later viz. H₂ and O₂ is different from that of H₂O, therefore the change is a chemical one.

Question 2.
Define a physical change?
Answer:
Physical change:
A physical change is a change in the physical properties (colour, state, density etc.) and does not involve a change in molecular structure. No new substance is formed and the change can be reversed by ordinary physical means.

Question 3.
Prove that evaporation of water and heating of iron to redness are physical changes?
Answer:
When water is heated, it changes into steam. No new substance has been formed because the molecular structures of water and steam are the same. Water has merely undergone a change in form (liquid → gas).

Further steam can be converted back into water just by the process of cooling therefore, this is a temporary change. Similary when iron is heated to redness, it is a temporary change in colour because on cooling iron is obtained back in its original form.

Question 4.
How can you argue that the following changes are physical changes:

1. Dissolution of sugar in water
2. Melting of wax
3. Lighting of bulb
4. Breaking of a chalk stick.

Answer:
1. Dissolution of sugar in water:
Is a physical change because no new substance is formed. On boiling off water, sugar can be obtained back.

2. Melting of wax:
When wax is heated in a dish, it melts but its composition does not change. On cooling we get back wax.

3. Lighting of bulb:
When an electric bulb is lighted by-passing electric current, the filament glows and emits light. But no new substance is formed. So it is a temporary change.

4. Breaking of a chalk stick:
When a chalk breaks, no new substance is formed. The identity of chalk aslo does not change. Therefore, it is a physical change.

Question 5.
Dispersion of a substance is a physical change or chemical one.
Answer:
Dispersion in solution:
This is also a physical change in many cases. The solute molecules get dispersed amongst the solvent molecules. They do not suffer a change in molecular structure and the solute can be recovered unchanged by cation of the solvent.

Question 6.
Give some chemical reactions which occurs in our daily life.
Answer:
Some important chemical reactions that occur in our daily life are:

1. Respiration (during respiration oxidation of glucose takes place).
2. Digestion of food.
3. Combustion of fuels.
4. Ripening of fruits.
5. Cooking of food.
6. Rusting of iron.

Question 7.
Explain that change in state is nothing but a physical change?
Answer:
Change in state:
All the substances can be transformed to gases, liquids or solids by changing temperature or the other physical conditions. In the solid state the constituent particles are ordred. In the liquid state they are less ordered; in the gaseous state they are most disordered. So, the physical state of a substance can be changed by application of energy.

Thus, changes of a solid to liquid i.e., melting of a solid, change of vapour to liquid etc. can be reversed by application of enerty i.e., either by supplying heat or by cooling. This leads to the conclusion that change of state is nothing but a physical change.

Question 8.
Why heating of a metal say platinum, to redness is a physical change?
Answer:
When platinum is heated to redness it glows. This is only due to temporary excitement of electrons in its atoms. When we stop heating in electrons get unexcited and consequently it ceases glowing. Therefore, change under consideration is definitely a physical change.

Question 9.
Explain as to why the following changes are chemical changes?

1. Rusting of iron
2. Souring of milk
3. Burning of magnesium
4. Pickling.

Answer:
1. Rusting of iron:
During the phenomenon new substances viz. iron oxide etc. are formed on the surface of iron. Iron cannot be obtained back from rust. So, rusting of iron is a chemical change.

2. Souring of milk:
As a result of souring of milk new sub¬stances are formed which cannot be converted back to milk, hence souring of milk is a chemical change.

3. Burning of magnesium:
When Mg burns new substance viz. magnesium oxide is formed, which cannot be converted back to magnesium and oxygen. Therefore burning of magnesium is a chemical change.
2Mg + O₂ → 2MgO

4. Pickling:
Pickling is nothing but the fermentation of the vegetable. Pickled vegetables cannot be changed back to fresh vegetables. Hence, it is also a chemical changed.

Question 10.
Give brief distinction between physical change and chemical change.
Answer:
Distinction between physical and chemical changes:
Physical Change:

• Change in physical properties.
• Temporary change.
• Composition of matter does not change.
• No new substance is formed.
• Can be reversed by physical means.
• Not accompanied by large energy changes.
• No change in weight.

Chemical Change:

• Change in chemical properties.
• More or less a permanent change.
• Composition of matter changes.
• New substance is formed.
• Cannot be reversed easily.
• Accompanied by large energy changes.
• Though total mass remains constant, mass of individual substance changes.

Question 11.
Is the solution of hydrogen chloride in water a physical changes?
Answer:
Hydrogen chloride is a covalent molecule. In solution it becomes electrovalent. The hydrogen ion combines with a water molecule to form hydronium ion. The properties of the solution are entirely different. There is a change in molecular structure and so as per our definition it is a chemical change.

Question 12.
Is an allotropic change a chemical change?
Answer:
The constituent atoms are identical in allotropes but allotropy is caused by change in molecular structure. Oxygen gas contains two atoms in each molecule but ozone contains three. In many cases the chemical as well as physical properties are different. So we have to conclude that allotropic change is a chemical change.

Question 13.
Is the cooking of rice a physical change?
Answer:
In cooking the fast molecules of boiling water pierce the walls of the cell in which strach is enclosed and release the starch. Sight hydrolysis also takes place. But the change is physical to a major extent since most of the starch remains unchanged.

Question 14.
What type of change is sublimation of ammonium chloride?
Answer:
Ammonium chloride on heating splits up into gases ammonia and hydrogen chloride. These gaseous products recombine on cooling to give the original salt. The apparent physical change is the result of two distinct chemical changes decomposition and combination. Sublimation can also be a physical change when the sub – stance is below its triple point and the change to vapour and back to solid state takes place directly, but in the case of ammonium chloride and many other compounds dissociation occurs.

Question 15.
Magnetisation of an iron bar is a physical change. Explain.
Answer:
Magnetisation of an iron bar:
Magnetisation caused by alignment of constituent atoms [figs, (a) and (b)] and as such it is to be considered only as a physical change. Charging and discharging of a condenser a temporary and physical change.

Physical and Chemical Changes Long Answer Type Question

Question 1.
Give in detail the distinction between physical and chemical changes?
Answer:
Distinction between physical and chemical changes:
As already stated a chemical change involves a change in the structure of the molecules while a physical change does not involve a change in molecular structure. This definition is comprehensive and all other characteristic of a chemical change can be deduced easily as floows.

1. During a chemical change new substances with new properties are produced:
Change in molecular structure means a new substance with new properties. On the other hand, a physical change does not involve a change in the molecular structure.

2. A chemical change is a permanent change and the original substance is not got back by reversing the conditions. A physical change is temporary and exist only as long as the imposed conditions exist. A physical change can be reversed by reversing the conditions.

3. No change, physical or chemical can take place without energy change. A large amount of heat energy has to be given to convert water into steam. But the energy involved in chemical changes is generally far greater than that involved in physical changes.

4. A chemical change means a physical change also, because won news substances with new properties are produced the physical state and physical properties are altered.

Question 2.
Give a detailed account of modem approach of physical and chemical changes?
Answer:
Modern approach of physical and chemical changes:
As your studies in science progress you will appreciate the point of view that all changes are chemical changes. Chemical changes are changes in structure. Minor electronic changes do occure even when a physical change takes place. In solids, subjected to heat, the ions oscillate with increasing amplitude and electrons move with greater speeds in expanded orbitals. Breaking a piece of diamond is an accepted chemical change because covalent chemical bonds are broken in the process. The same is happening when any substance is broken.

Thedivision into physical and chemical changes is, therefore, purely a matter of convenience. The three types of changes are classified as fallows:

1. Physical change:
Slight changes in outer electron states. Comparatively less energy change. No change in molecular patterns. No change in nucleonic pattern.

2. Chemical change:
Change in molecular pattern. Large scale energy change. Rearrangement, of electronic orbitals. No change in nucleonic pattern.

Question 3.
What are slow and fast reactions? Give example.
Answer:
A reaction can be called slow or fast depending upon the speed rate of reaction.
Whenever elements and compounds react their reaction is said to be slow if the rate of the reaction, i.e., the quantity of products obtained per unit time from the reactants, is slow.
Example:

1. Rusting of iron is a slow reaction.
2. When a copper vessel kept in moist air it gets greenished due to the formation of basic copper carbonate. To the contrary if the speed or the rate of the reaction is fast, than the reaction is said to be the fast reaction.

Example:
By adding sodium chloride in silver nitrate solution, immediately a white ppt. appears. It is a fast reaction i.e.,

Question 4.
What is a chemical reaction? Give an example.
Answer:
A reaction in which the following are being occurred is called a chemical reaction:

1. Absorption or liberation of heat or any other form of energy.
2. Change in the identity of the combining substances i.e., the reactants.
3. Collision among the reactant molecules.
4. Use of some catalyst or provision of some form of energy to the reactants for initiation of reaction.

Example:
1. Sodium reacts with water to form sodium hydroxide alongwith the liberation of hydrogen gas.
The chemical equation of the reaction is as follows:
2Na + 2H₂O → NaOH + H₂

2. Lime stone, on heating, liberates carbon dioxide.
The equation for the reaction is as follows:
CaCO₃ → CaO + CO₂.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 18 Wastewater Story

Activities

Activity – 1
We have given one example of the use of clean water. You can add many more?

Answer:

Activity – 2
Locates an open drain near your home, school or on the roadside and inspect water flowing through it? Record color, odour and any other observation. Discuss with your friends and your teacher and fill up the following Table?
Table: Contaminant survey

Wastewater Story Text Book Exercises

Question 1.
Fill in the blanks:

1. Cleaning of water is a process of removing ……………………….
2. Waste – water released by houses is called ………………………
3. Dried ……………………… is used as manure.
4. Drains get blocked by …………………….. and ………………………..

Answer:

1. Contaminants
2. Sewage
3. Dung
4. Plastic, sludge.

Question 2.
What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas?
Answer:
Sewage is waste – water released by homes, hospitals, offices, industries and other users. It also includes rainwater that has run down the street during a heavy rain or storm. The water that washes off roads and roof tops carries harmful substances with it. Basically sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities which are called contaminants. That is why it is harmful to discharge untreated sewage in to rivers or seas.

Question 3.
Why should oils and fats be not released in the drain? Explain.
Answer:
Oils and fats should not be released in the drains because they harden the soil in the pipes and block them. Fats get clogged in the holes of the soil in the drain and block it. It does not allow the waste – water to flow and thus the whole sewer system is blocked.

Question 4.
Describe the steps involved in getting clarified water from waste – water?
Answer:
Treatment of waste – water involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the waste – water.

1. Waste – water is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.

2. Water goes to a grit and sand removal tank. The speed of the incoming waste-water is decreased to allow sand, grit and pebbles to settle down.

3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the float able solids like oil and grease. Water so cleared is called clarified water.

4. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The bio gas produced in the process can be used as fuel or can be used to produce electricity.

5. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

Question 5.
What is sludge? Explain how it is treated?
Answer:
Sludge is the collected solid waste from the waste – water during the treatment in water treatment plant. Sludge is decomposed in a separate tank by the anaerobic bacteria. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.

Question 6.
Untreated human excreta is a health hazard? Explain?
Answer:
Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include chlorea, typhoid, polio, meaningities, hepatitis and dysentery.

Question 7.
Name two chemicals used to disinfect water?
Answer:
Ozone, chlorine.

Question 8.
Explain the function of bar screens in a waste – water treatment plant?
Answer:
Bar screens clear the waste – water of all the physical impurities. Large waste objects like napkins, plastics, can sticks, rags etc. are removed from the waste – water through the bar screens.

Question 9.
Explain the relationship between sanitation and disease?
Answer:
Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for walls, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery. That is proper sanitation is must to avoid some of the deadliest diseases.

Question 10.
Outline your role as an active citizen in relation to sanitation?
Answer:
As active citizen we should take care of our personal and environmental sanitation. We should make people around us, aware of the benefits of sanitation we should help the municipal corporations and gram panchayats to cover all the open drains and remove the unhygienic and disease causing substances thrown in open.

Question 11.
Here is a crossword puzzle: Good luck!

Across

1. Liquid waste products
2. Solid waste extracted in sewage treatment
3. A word related to hygiene
4. Waste matter discharged from human body.

Down

1. Used water
2. A pipe carrying sewage.
3. Micro – organisms which causes cholera.
4. A chemical to disinfect water.

Answer:

Question 12.
Study the following statements about ozone:

1. It is essential for breathing of living organisms.
2. It is used to disinfect water.
3. It absorbs ultraviolet rays.
4. Its proportion in air is about 3%.

Which of these statements are correct?

1. (a), (b) and (c)
2. (b) and (c)
3. (a) and (d)
4. All four.

Answer:

2. (b) and (c).

Extended Learning – Activities and Projects

Question 1.
Construct a crossword puzzle of your using the keywords?
Answer:

Across:

1. Mixing with air.
2. Decomposed product of leaves.
3. Does not read oxygen
4. Needs oxygen.

Down:

1. Necessary for hygiene
2. Solid waste
3. Pipes to carry sewage

Question 2.
Then and now: Talk to your grand parents and other elderly people in the neighbourhood? Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief report on the information you collected?
Answer:
Do yourself.

Question 3.
Visit a sewage treatment plant?
It could be as exciting and enriching as a visit to a zoo, a museum, or a park? To guide your observation here are a few suggestions?

Record in your notepad:
Place ……………….. Date …………………… Time
Name of the official at the plant ………………………. Guide/Teacher …………………………

1. The location of the sewage plant.
2. Treatment capacity.
3. The purpose of screening as the initial process?
4. How is air bubbled through the aeration tank?
5. How safe is the water at the end of the treatment? How is it tested?
6. Where is the water discharged after treatment?
7. What happens to the plant during heavy rains?
8. Is bio gas consumed within the plant or sold to other consumers?
9. What happens to the treated sludge?
10. Is there any special effort to protect nearby houses from the plant?
11. Other observations.

Answer:
Do with the help of your subject teacher.

Wastewater Story Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative :

Question (a)
This is not the cause of water pollution?
(a) Floods
(b) Rains
(c) Chemicals
(d) Open defecation.
Answer:
(b) Rains

Question (b)
To improve sanitation following new technique is being used?
(a) Vermi – processing toilets
(b) Sewer system
(c) Onsite sewage disposal
(d) Both (a) and (b).
Answer:
(d) Both (a) and (b).

Question (c)
Following should not be disposed off in the drains?
(a) Tissue Papers
(b) Excreta
(c) Oils and Fats
(d) Waste water.
Answer:
(c) Oils and Fats

Question (d)
Following process is not a part of waste – water treatment?
(a) Decomposition
(b) Grit and Sand Removal
(c) Evaporation
(d) Chlorination.
Answer:
(c) Evaporation

Question (e)
Polluted water causes disease likes –
(a) Hepatitis
(b) Typhopid
(c) Cholera
(d) Diarrhoea.
Answer:
(c) Cholera

Question (f)
In a public sewerage system, the largest sewers are –
(a) Filters
(b) Interceptors
(c) Waterways
(d) None of these.
Answer:
(b) Interceptors

Question 2.
Fill in the blanks:

1. …………………… bacteria is used to treat sludge.
2. Sewage is a liquid waste which causes water and soil
3. Waste – water is treated in a sewage treatment ………………………
4. …………………… and …………………….. are the products of water clarification.
5. By – products of waste – water treatment are sludge and ………………………
6. Addition of disease causing organisms in water is called water …………………….
7. …………………………… in open cause health hazards.
8. ……………………….. is used as manure.
9. To improve sanitation, low cost ……………………….. sewage disposal systems are being encouraged.
10. Adopting good sanitation practices should be our way of ……………………………….

Answer:

1. Anaerobic
2. Pollution
3. Plant
4. Sludge and bio gas
5. Bio – gas
6. Contamination
7. Defecation
8. Activated sludge
9. Onsite
10. Life.

Question 3.
Which of the following statements are true (T) or false(F):

1. Sewage contains pure water for drinking.
2. Used water is waste – water.
3. Waste – water could not be reused.
4. Open drain system is a breeding place for flies.
5. Manholes are located at every 50 m to 60 m in the sewerage.
6. Waste – water is passed through for screens.
7. Eucalyptus trees absorb all surplus waste – water rapidly and release pure water vapour into the atmosphere.

Answer:

1. False
2. True
3. False
4. True
5. True
6. True
7. True.

Wastewater Story Very Short Answer Type Questions

Question 1.
Define sewage?
Answer:
Sewage is water that contains waste products produced by human beings. It is also called waste water.

Question 2.
Which is the world water day?
Answer:
22nd March.

Question 3.
Which is proclaimed as the International Decade for action on water for life?
Answer:
United Nations proclaimed the period 2005 – 2015 as the international Decade for action on “Water for life”.

Question 4.
What do you mean by cleaning of water?
Answer:
Cleaning of water is a process of removing pollutants before it enters a water body or is reused.

Question 5.
What is sewage treatment?
Answer:
This process of wastewater treatment is commonly known as “Sewage Treatment”.

Question 6.
In how many steps sewage treatment divided?
Answer:
The sewage treatment in most cities involve two main steps primary and secondary treatment. Some cities also require an additional step called tertiary treatment.

Question 7.
What do you mean by primary treatment?
Answer:
The primary treatment removes the heaviest solid material from sewage. This process removes about half the suspended solids and bacteria in sewage. Sometimes chlorine gas is added to kill most of the remaining bacteria.

Question 8.
What do you mean by secondary treatment?
Answer:
The secondary treatment removes from 85% to 90% of the solids and oxygen consuming wastes remaining in sewage after it has undergone primary treatment. The most common methods of secondary treatment are the activated sludge process and the trickling filtration process.

Question 9.
Why should we plant eucalyptus along sewage ponds?
Answer:
These trees absorb all surplus waste – water rapidly and release pure water vapour into the atmosphere.

Question 10.
Write certain inorganic impurities in the waste – water?
Answer:
Metals, phosphates and nitrates.

Question 11.
Name certain disease causing micro – organism?
Answer:
Bacterias, Viruses etc.

Question 12.
Which process removes the solids like faces and other substances from the waste – water?
Answer:
Grit and sand removal tank.

Question 13.
How is sand, grit on pebbles settled down?
Answer:
Water goes to a grit and sand removal tank. The speed of the incoming waste-water is decreased to allow sand, grit and pebbles to settle down.

Question 14.
How is dry sludge used?
Answer:
Dried sludge is used as manure, returning organic matter and nutrients to the soil.

Question 15.
Who decomposes the sludge?
Answer:
Anaerobic bacteria decompose the sludge.

Question 16.
Which instrument is used to remove floatable solids from the waste – water?
Answer:
A skimmer is used to remove floatable impurities.

Question 17.
What helps to clean the clarified water?
Answer:
Aerobic bacteria helps to clean the clarified water.

Question 18.
Why is ozone and chlorine used?
Answer:
Ozone and chlorine is used to kill the bacteria etc. present in the clarified water.

Question 19.
Why is air pumped to clarified water?
Answer:
Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.

Wastewater Story Short Answer Type Questions

Question 1.
Explain sewage?
Answer:
Waste water including human excreta which flows from our homes into the drains is called domestic sewage. This contains microbes which cause water – borne diseases. This waste water is often dumped into water bodies.

Question 2.
How is water polluted?
Answer:
Water is used various purposes in homes, industries and agriculture. When water is used for cleaning, bathing, washing, dying etc. it pollutes the water. Unwanted waste materials and chemicals etc get added in the water and this wastes the water.

Question 3.
What is done to improve sanitation?
Answer:
To improve sanitation, low cost onsite sewage disposal stem are being encouraged. Examples are septic tanks, chemical toilets, composting pits. Septic tanks are suitable for places where there is no sewerage system, for hospitals isolated buildings or a Luster of 4 to 5 houses.

Question 4.
What is vermi process toilet?
Answer:
A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, j low water – use toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes resource much needed for soil.

Wastewater Story Long Answer Type Questions

Question 1.
How defection in open cause health hazards?
Answer:
Due to lack of proper sewage disposal system a large amount of people in India defecates in open. They use riverbeds, railway lines, fields and drains for this purpose. These excreta dries down and percolate in soil with rain water. It pollutes the ground water.

Excreate along river bed pollutes the river water. In this way water on the ground and under the ground get polluted. This polluted water contains the micro – organisms of various communicable diseases like cholera, typhoid, hepatitis and meaning it is dysentery etc.

Question 2.
Suggest some better house keeping practices?
Answer:

1. Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats dog the soil pores redunt. Its effectiveness in filtering water. Oil and fats should he thrown in the dustbin.

2. Chemicals like paints, vents, insecticides, motor oil, medicines may kill microbes it help purity water. So they should not be thrown in the drain.

3. Used ten – leaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin. These waste choke the drains. They do not allow free flow of oxygen. This hampers the degradation process.

Question 3.
What is the composition of sewage?
Answer:
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities. nutrients, saprotrophic and disease causing bacteria and other microbes.

1. Organic impurities:
Human faces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste, etc.

2. Inorganic impurities:
Nitrates, phosphates, metals. Nutrients Phosphorus and nitrogen.

3. Bacteria:
Such as which cause cholera and typhoid.

4. Other microbes:
Such as which cause dysentery.

Question 4.
How is sewage treated?
Answer:
Domestic sewage should be treated before being discharged into the river. Sewage is treated by first separating the solid material by sedimentation and filtration. Compressed air is then passed through the liquid which is then chlorinated to kill micro – organisms. The solid matter separated from sewage can be used to generated bio gas which can be used as fuel. The sludge that is left can be used as manure in the fields to grow organic foods.

Question 5.
What are the different ways in which solid waste can be disposed off?
Answer:
The different ways are as:

1. Domestic wastes like fruit and vegetable waste, leftover food, leaves of potted plants can be converted into compost and used as manure.
2. Most of the solid waste is buried in low lying areas to level uneven land. This is called landfill.
3. Wastes coming from industries such as metals can be recycled and used again.
4. Broken plastic articles like plastic bags, buckets, bowls, cups, plates, etc. can be melted and remolded to make new articles.
5. The waste disposal on a large scale is done by the municipality of a city using incinerators. The solid waste is burnt at high temperature. Ash is removed from time to time.

Question 6.
Explain sewage treatment plant.
Answer:
Sewage is water that contains waste products by human beings. It is also known as waste water. In fact sewage comes from the sinks and toilets of homes, restaurants, factories and office buildings. The sewage mainly consists of dissolved material that cannot be seen and bits of such solid matter as human waste and ground up rubbish.

It also contains harmful chemical and disease producting bacteria. Most sewage ultimately goes into lakes, rivers and oceans. However, in many western nations, the sewage is treated in some way before it goes into the waterways as a semi – clear liquid called effluent. Most methods used to treat sewage convert organic sewage into inorganic compounds viz. nitratres, sulphates and phosphates. Some of these compounds serve as food for algae. As the algae decay using excess of oxygen from water, the fish and plants in water will ultimately die.

Question 7.
Explain rural sewerage system?
Answer:
Many rural areas not served by public sewers. In such areas, most home owners use septic tanks to treat their sewage. These tanks are concrete or steel containers buried underground at home and buildings. Sewage flows into a septic tank through a pipe connecting the tank with a building.

Solids in the sewage sink to the bottom of the tank as sludge or float to the surface as scum. Effluent then flows from the tank into a system of pipes with open joints that allow sewage effluent to be gradually distributed into the soil. The soil bacteria then destroy the remaining organic material in the influent.

In a septic tank, bacteria in the sewage attack and digest the sludge and scum. The digestion process changes most to the wastes into gas and a harmless substance called humus. The gas then escapes into the air. The humus in the tank should be pumped our periodically and taken to a sewage treatment plant.

Question 8.
Explaining urban sewerage system?
Answer:
In a public sewerage system, the largest sewers, known as interceptors, carry the sewage to a wastewater treatment plant. The sewage treatment in most cities involves two main steps, primary treatment and secondary treatment. Some cities also require an additional step called tertiary treatment. At a treatment plant, sewage first passes through a screen that traps the largest pieces of matter. It then flows through a grit chamber, where heavy inorganic matter, such as sand, settles down.

The liquid next flows into a large primary sedimentations tank. Many suspended solids sink to the bottom of this tank and form a muddy material called sludge. Grease floats to the surface, where it is removed by a process called skimming. The effluent is then released into waterways.

Primary treatment removes bout half of the suspended solids and bacteria in sewage. Sometimes chlorine gas is added after primary or secondary treatment to kill most of the remaining bacteria. The secondary treatment removes about 85 to 90 percent of the solids and oxygen consuming wastes remaining in sewage after it has undergone primary treatment.

Question 9.
Explain the most common methods of secondary treatment in urban sewerage system?
Answer:
The most common methods of secondary treatment are:

1. The activated sludge process.
2. The trickling filtration process.

In case of activated sludge process, the influent from the primary sedimentation tank flows into a second tank called an aeration tank. The useful bacteria move through the liquid and change the organic matter into less harmful substances. The liquid then flows into a final sedimentation tank, where the sludge settles down to the bottom.

The influent is then discharged into waterways. In case of trickling filtration process, the filters are filled with crushed rocks. As sewage is distributed over the rocks, it reacts with slime that develops on the rocks. The slime contains useful bacteria that change organic material in the sewage into less harmful substances. These substances are removed in a final sedimentation tank, where they fall to the bottom as sludge.

Sometimes tertiary treatment is also used after primary and secondary treatment to produce purer effluent. The tertiary treatment methods include chemical treatment, microscopic screening, radiation treatment, etc. Tertiary treatment makes effluent safer to discharge into waterways.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 5 Acids, Bases and Salts

Acids, Bases and Salts Intext Questions

Question 1.
Can I taste all substances to find their taste?
Answer:
No, we should not taste unknown substances. They could harm us.

Question 2.
I am not getting the same result when using solid baking soda on dry litmus paper. Why?
Answer:
Make a solution of baking soda and then try.

Activities
Activity 1
Let us recall tastes of some edible substances listed in table. If you have not tasted any of these substances taste it now and enter the result in the given table.
Answer:

Activity 2
Mix some water with lemon juice in a plastic cup/ tumbler/ test tube. Put a drop of the above solution on a strip of the red litmus paper with the help of a dropper.

• Is there any change in colour.
• Repeat the same exercise with the blue litmus paper.
• Note down if there is any change in colour.

Perform the same activity with the following substances:
Tap water, detergent solution, aerated drink, soap solution, shampoo, common salt solution, sugar solution, vinegar, baking soda solution, milk of magnesia, washing soda solution, lime water. If possible make solutions in distilled water. Record your observations as in table.
Answer:

Activity 3
Take a tablespoonful of turmeric powder. Add a little water and make a paste.
Make turmeric paper by depositing turmeric paste on blotting paper/filter paper and drying it. Cut thin strips of the yellow paper obtained.

• Put a drop of soap solution on the strip of turmeric paper.
• What do you observe
• Similarly test the solutions listed in table and note down your observations.

Answer:
The turmeric turns red.

Acitivity 4
Collect some China rose (Gudhal) petals and place them in a beaker. Add some warm water. Keep the mixture for some time till water becomes coloured. Use the coloured water as an indicator. Add five drops of the indicator to each of the solutions given in table:

Acids, Bases and Salts Text book Exercises

Question 1.
State ditterences between acids and bases?
Answer:
Differences between acids and bases:
Acids:

1. Acids are substances which contain one or more replaceable hydrogen atoms.
2. All acids are sour in taste.
3. All acids turn blue litmus red.
4. Acids are compounds that contain hydrogen.
5. Acids react with metal to form salts and release hydrogen gas.

Bases:

1. Bases are substances which have one or more replaceable hydroxyl group (OH).
2. Bases are bitter in taste and slippry in touch.
3. Bases turn red litmus blue.
4. Bases are compound which have hydroxyl group.
5. Bases react with acids to form salts.

Question 2.
Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer:
Basic.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is extracted from lichens. It is used as indicator.

Question 4.
Is the distilled water acidic/basic/neutral? How would you verify it?
Answer:
The distilled water is neutral.

Put a drop of distilled water on a strip of the red litmus paper with the help of a droper. We observe that colour of the litmus paper is not change. The solutions which do not change the colour of either red or blue litmus are knwon as neutral solutions. These substances are neither acidic nor basic.

Question 5.
Describe the process of neutralisation with the help of an example?
Answer:
The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water
Example: Following reaction:
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false:

1. Nitric acid turn red litmus blue. (T/F)
2. Sodium hydroxide turns blue litmus red. (T/F)
3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
4. Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
5. Tooth decay is caused by the presence of a base. (T/F)

Answer:

1. False (F)
2. False (F)
3. True (T)
4. True (T)
5. False (F).

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve tire drinks on the demand of customers. One customer wants acidic drind, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Answer:

1. He can decide by the use of indicator.
2. It the sample of drink turns red litmus blue, it is basic. It it turns blue litmus red, it is acidic.
3. It it does not effect litmus, then it is neutral.

Question 8.
Explain why?

1. An antacid tablet is taken when you suffer from acidity.
2. Calamine solution is applied on the skin when an ant bites.
3. Factory waste is neutralised before disposing it into the water bodies.

Answer:
1. Our stomach contains hydrachloric acid. It help us to digest food. But too mcuh of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

2. Ant injects an acid (i.e., formic acid) during bite which cavses the burning sensation. Calamine solution is basic in nature. It neutralises the acid and relives us from the pain.

3. Factory wastes contain both acidic and basic substances. If they are allowed to flaw into the water bodies, they are harmful for orgainsms living in water. So the factory wastes are neutralised by adding basic substances.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Answer:
Turmeric solution turns red in contact with bases. It is not affected by acids and neutral substances. So, first we will identify the base.

Now, the base is taken and turmeric is added. It will turn red. Then, one of the solutions is added to it gradually. If the solution turns yellow again, the added liquid is hydrochloric acid because it neutralises the base. Otherwise the added liquid is sugar solution.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The nature of the solution is neutral, because the solutions which do not change the colour of either red or blue litmus are known as neutral solution. These substances are neither acidic nor basic.

Question 11.
Consider the following statements:

1. Both acids and bases changes colour of all indicators.
2. If an indicator gives a colour change with an acid, it does give a change with a base.
3. If an indicator changes colour with a base, it does not change colour with an acid.
4. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

1. All four
2. (a) and (d)
3. (b) and (c)
4. only (d)

Answer:
4. only (d).

Extended Learning – Activities and Projects:

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works?
Answer:
Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table?
Answer:
Do with the help of your subject teacher.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner?
Answer:
Do yourself.

Question 4.
Visit a doctor. Find out the medicines, he prescribes to treat acidity Ask him how acidity can be prevented?
Answer:
Do yourself.

Acids, Bases and Salts Additional Important Questions

Objective Type Questions

Question 1
Choose the correct alternative

Question (i)
Bases are –
(a) Sour in taste
(b) Sweet in taste
(c) Bitter in taste
(d) None of the above.
Answer:
(c) Bitter in taste

Question (ii)
Blue litmus turns red by –
(a) Sodium
(b) Sodiujn sulphate
(c) Bitter in taste
(d) Qattstic potash.
Answer:
(c) Bitter in taste

Question (iii)
Which one of the following oxides will react with acids to salt and water –
(a) CO
(b) SO₂
(c) SO₃
(d) CuO.
Answer:
(d) CuO.

Question (iv)
Which of the following is a mineral acid –
(a) Acetic acid
(b) Citric acid
(c) Tartaric acid
(d) Nitric acid.
Answer:
(d) Nitric acid.

Question (v)
Which is the common name of sodium bicarbonate –
(a) Caustic soda
(b) Washing soda
(c) Blue vitriol
(d) Baking soda.
Answer:
(d) Baking soda.

Question (vi)
For diluting acid –
(a) Water is added to acid.
(b) Acid is added to water.
(c) Acid is boiled after adding water.
(d) Acid is boiled before adding water.
Answer:
(c) Acid is boiled after adding water.

Question (vii)
……………. is used for white – washing in house.
(a) Sodium hydroxide
(b) lime stone, calcium hydroxide
(c) blue vitriol
(d) lime water and ash.
Answer:
(b) lime stone, calcium hydroxide

Question (viii)
Nausadar is –
(a) Acid
(b) Alkali
(c) Salt
(d) Indicatior
Answer:
(c) Salt

Fill in the blanks:

1. Acetic acid is present in while is present ………….. While …………. is present in lemon.
2. Magnesium burns in air to form …………. which is ………….. oxide.
3. The chemical formula of slaked lime is ……………..
4. Acids are …………….. in taste.
5. The gas which escapes out from many aerated soft drinks is …………..
6. ………….. are slippery in touch.
7. Bases turn ………….. litmus to …………..
8. In a neutralisation reaction an ………….. and an ………….. combine to form a salt and water.
9. The solution formed by reacting P₂ O₅ with H₂O turns ………….. litmus ……………
10. Methyl orange is a good ……………

Answer:

1. Vinegar, citric acid
2. Magnesium oxide, basic
3. Ca₂, (OH)₂
4. Sour
5. CO₂
6. Bases
7. Red, blue
8. Acid, alkali
9. Blue, red
10. Indicator.

Question 3.
Which of the following statements are true (T) or false (F):

1. Acids have a bitter taste.
2. Bases have a bitter taste.
3. Bases react with carbonate to liberate carbon dioxide.
4. Copper does not reach with tamarind (imli) water.
5. Sulphuric acid is c.’led ‘King of chemicals’.
6. Orange juice turns blue litmus red.
7. Alum (Phitkari) acts as a antacid.
8. Soaps are salts of fatty acids.
9. Copper sulphate is used as a preservative in pickels. Potassium chloride is a salt of sulphuric acid.

Answer:

1. False
2. True
3. False
4. True
5. True
6. True
7. False
8. True
9. False
10. False.

Question 4.
Paheli brought the following paheli (riddle) for you.

1. Coffee is brown
2. And bitter in taste
3. Is it an acid
4. Or a base
5. Don’t give the answer
6. Without any test
7. You are in the dark With its taste

Answer:
Acidic.

Acids, Bases and Salts Very Short Answer Type Questions

Question 1.
Which acid is present in our stomach?
Answer:
Hydrochloric acid in small amount is present in our stomach.

Question 2.
What will you do if some acid is split on the table?
Answer:
We will sprinkle some base on the table to neutralise the effect of the acid.

Question 3.
Why antacids tablests are used to reduce acidity of the stomach?
Answer:
Sometimes due to spicy food the concentration of hydrochloric acid increases in the stomach. This causes acidity. To reduce it some harmless bases are used like milk of magnesia [Mg (OH)₂] and aluminium hydroxide, which balance the excess of acids. These are solid in the form of tablets called antacids.

Question 4.
What are mineral acids? Give two examples.
Answer:
The acids which are capable of forming hydrogen ions, when dissolved in water are mineral acids. For example, HCl, HNO₃, H₂SO₄ (Hydrochloric acid, Nitric acid, Sulphuric acid). In other words, mineral acids are strong acids. These acids are called mineral acids because these are prepared from minerals.

Question 5.
What are organic acids? Give two Examples.
Answer:
Organic acid are soured milk, lemon, green mangoes and karvanda are sour tasting. All of them contain some naturally occurring acids. Such acids are found in animals and plant materials. They are known as organic acids.
Examples: Lactic acid, Citric acid, Vinegar, Formic acid.

Question 6.
What do you understand by concentrated and dilute acids?
Answer:
Concentrated acid:
The acids which are prepared by dissolving in water, are known as concentrated acid.

Dilute acid:
The acid which are prepared by dissolving in excess amount of water are known as dilute acids.

Question 7.
Name the gas obtained when a metal carbonate reacts with an acid?
Answer:
When metal carbonate reacts with acids they give carbon dioxide gas.

Question 8.
What will happen if blue litmus paper is soaked in orange juice?
Answer:
It change into red colour.

Question 9.
State one characteristic property of all acids. Is dry hydrogen chloride gas an acid?
Answer:

1. Acids have a sour taste.
2. Acids turn blue litmus red.
3. Acids react with metal to evolve hydrogen gas.
   2HCl + Mg → MgCl₂ + H₂
   Yes, hydrogen chloride is an acid.

Question 10.
A solution turns red litmus paper into blue. What does this indicate about the chemical nature of the solution?
Answer:
The solution which turns red litmus paper blue is basic in nature. The substance which turns red litmus paper blue is known as alkalies.

Question 11.
Classify the following chemicals in acids and bases:
KON, HNO₃, Ca(OH)₂, LiOH, CH₃COOH, HCOOH, Mg(OH)₂, NaOH, H₂SO₄, HCl
Answer:
Acids:
HNO₃, H₂SO₄, HCl.

Bases:
KOH, Ca(OH)₂, LiOH, CH3COOH, HCOOH, Mg(OH)₂, NaOH.

Acids, Bases and Salts Short Answer Type Questions

Question 1.
You are given hydrochloric acid solution, sodium hydroxide solution and water in three different bottles. How will you check which bottle has which compound?
Answer:
Take three pieces of blue litmus paper. Put one piece of blue litmus paper into each of these solutions. That bottle which turns blue litmus red contains hydrochloric acid. Take three pieces of red litmus paper. Put one piece of red litmus paper into each of these solutions. That bottle which turns red litmus blue contains sodium hydroxide (base).

Question 2.
How can you test the presence of acid in a substance?
Answer:
Acids can be tested in any substance by the following methods:

1. Take a drop of the dilute solution of the substance on the tips of your tongue. If it taste sour, it is acid.
2. Place a blue litmus paper in the solution. If the colour changes to red, acid is present.

Example: 2Na + 2HCl → 2NaCl + H₂

Question 3.
What are indicators? Name two acid – base indicators.
Answer:
The substance which are used to identify whether a substance is an acid or base is called indicators. For example, litmus solutions give red colour with acids and blue colour with bases. Therefore, litmus is used as indicator. Substances wrhich given differnet colours with acid and base are called acid – base indicators.
Example:

1. Methyl orange
2. Phenolpthalein

Question 4.
State the colour of dry litmus paper when placed in separate samples of dilute sulphuric acid, moist ammonia gas, moist chlorine, sodium hydroxide, lemon juice, vinegar and water into which sulphur dioxide gas has been bubbled for some time?
Answer:

Question 5.
Why are acids not stored in metal containers? Containers/ vessels made from which material are safe to store acids?
Answer:
All the acids react with metals. They react vigorously and slowly with metals according to their nature. So, the acids are not stored in metal containers. Vessels made from glass or cermics are considered safe for strong acids.

Question 6.
Which acids are present in following substance:

Answer:

1. Citric acid
2. Acetic acid
3. Lactic acid
4. Oxalic acid
5. Tartaric acid.

Question 7.
Why does colour of blue vitriol change when heated?
Answer:
When we blue vitriol heated it changes into white vitriol and water.

Question 8.
Write one use of each of the following compounds?

1. Vinegar
2. Methly orange
3. Alum
4. Sulphuric, acid
5. Sodium hydroxide.

Answer:

1. In pickles and jam for preserving it in good condition for long duration.
2. As a indicator.
3. In purifying water.
4. In purifying pertroliujn products.
5. In purifying pertrolium products.

Question 9.
What are acid salts? Give two examples?
Answer:
Acid salt:
When a strong acid is neutralised by a weak base, then a salt is formed, such type of salt is called acid salt.
For example:
H₂SO₄ + 2NH₄OH → (NH ) SO₄ + 2H₂O
HCl+ NH₄OH → NH₄Cl + H₂O

Question 10.
Complete the following equations:

1. NaOH + H₂SO₄ → ……………. + H₂O
2. H₂CO₃ + NaOH → ……………. + H₂O
3. HNO₃ + KOH → ……………. + H₂O
4. Mg (OH)₂ + 2HCl → ……………. + 2H₂O

Answer:

1. NaOH + H₂SO₄ → Na₂SO₄ + H₂O
2. H₂CO₃ + 2NaOH → Na₂CO₃ + 2H₂O
3. HNO₃ + KOH → KNO₃+ H₂O
4. Mg (OH)₂ + 2HCl → + MgCl₂ + 2H₂O

Question 11.
Name the gas obtaines when a metal carbonate reacts with an acid?
Answer:
When metal carbonate reacts with acids they give carbon dioxide gas.
For example.

Question 12.
Differentiate between bases and alkalies by giving suitable examples of each?
Answer:
Bases:
Bases are the compound which have one or more hydroxyl group (OH) in their molecule.
Examples: NaOH, Ca(OH)₂, KOH etc.

Alkalies:
Water soluble bases are called alkalies.
Examples: Sodium hydroxide, potassium hydroxide and calcium hydroxide.

Question 13.
What is a neutralisation reaction? Give two examples.
Answer:
The reaction of an acid with an alkali and vice – versa to form salt and water is called neutralisation reaction.
For examples:

Question 14.
How is salt obtained from sea – water?
Answer:
The seas are great sources of salts. A litre of a water contains about 35 grams of salts. Sodium chloride is the main salt. The sea water is trapped in shallow called lagoons and is allowed to evaporate in sunlight to white solid crystal of salts. These crystals are processed and packed to send to markets.

Question 15.
What are the uses of weak alkalies?
Answer:

1. Ammonia is a weak alkali. It is used for the manufacture of fertilizers.
2. Ammonia is also used for the production of wood pulp and organic chemicals.
3. It is also used for making synthetic fibres such as nylon and nitric acid, which are used for the preparation of synthetic cloth.
4. Calcium hydroxide is used in the manufacture of bleaching powder.

Question 16.
Tabulate the some hydrated salts with their chemical formulae and colour?
Answer:
Some hydrated salts:

Question 17.
Name some common acid and alkali indicators?
Answer:

Acids, Bases and Salts Long Answer Type Question

Question 1.
What are acids? Write their properties.
Answer:
Acids are substances which contain one or more replaceable hydrogen atoms. Its properties are:

1. 1. All acids are sour in taste.
   2. All acids turn blue litmus red.
   3. Acids are compounds that contain hydrogen e.g., H₂SO₄, HCl etc.
   4. Acids are compounds which form hydronium ion (H₃O⁺) in aqueous (water) solution.
      Example:
      

1. Acids react with metal to form salts and release hydrogen gas.
   Example: 2Na + 2 HC1 → 2NaCl + H₂
   
2. Acids react with carbonates and bicarbonates to give carbon dioxide gas.
   Example:
   

Question 2.
What are bases? Write down its properties.
Answer:
Bases are substances which have one or more replaceable hydroxyl group (OH).
The various properties of bases are:

1. Bases are bitter in taste and slippery in touch.
2. Bases turn red litmus blue.
3. Bases are compound which have hydroxyl group.
4. All bases give hydroxyl ion into aqueous solutions.
   
5. Bases react with acids to form salts.
   Example: NaOH + HCl → NaCl + H₂O

Question 3.
What are the uses of mineral acids in industry?
Answer:
The uses of mineral acids in industry are:

1. Concentrated sulphuric acid, nitric acid and hydrochloric acid are used in a large number of metallurgical operations, manufacture of fertilizers and preparations of large number of industrial chemicals.

2. Hydrochloric acid is used for removing the deposits from inside the boilers. This process is known as descaling.

3. One of the mineral acid, hydrochloric acid (HCl) present in our stomach helps in digestion of food.

4. Nitric acid (HNO₃) is used by goldsmiths for cleaning gold and silver ornaments.

Question 4.
Distinguish clearly between the following terms by giving suitable examples:

1. Organic acid and mineral acid.
2. Base and alkali.

Answer:
1. Organic acid:

• Organic acid contains COOH functional group.
• These acids are weak.
• These acids are present in humans and plants.
• They are less corrosive and are used in food ingradients.
  Examples: Ethanoic acid, lactic acid, citric acid.

Mineral acid:

• Mineral acid contains hydrogen ions (H⁺).
• These acids are strong.
• These acids are prepared by mankind.
• They are corrosive in nature and have industrial use.
  Examples: Hydrochloric acid, sulphuric acid, nitric acid.

2. Base:

• Bases are the compound which have one or more hydroxhyl group (OH) in their molecule.
• All alkalies are bases
• Bases are insoluble in water.
  Examples: NaOH, Ca(OH)₂, KOH

Alkali:

• Water soluble bases are called alkalies.
• All bases are not alkalies.
• Alkalies are soluble in water.
  Examples: Sodium hydroxide potassium hydroxide and calcium hydroxide.

Question 5.
Write any three most common salts used in daily life and write their uses?
Answer:
Most common salts used in daily life are:
1. Washing Soda: Na₂CO₃.10H₂O.
Uses:

• It is used in laundary.
• It is used to prepare other compounds such as glass, caustic soda and detergent poweders.

2. Baking Soda: NaHCO₃
Uses:

• It is used in baking powder.
• It is used as medicine to reduce acidity of the stomach.
• It is used in fire extinguisher.

3. Potash alum or phitkari:
K₂SO_4.Al₂(SO₄)₃24H₂O
Uses:

• It is used to purify water.
• It is used after shave to stop the bleeding from cuts.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 17 Forests: Our Lifeline

Forests: Our Lifeline Intex Questions

Question 1.
What would happen if forests disappear?
Answer:

1. If forests disappear, the amount of carbon dioxide in air will increase, resulting in the increase of earth’s temperature.
2. In the absence of trees and plants, the animals will not get food and shelter.
3. In the absence of trees, the soil will not hold water which will cause floods.
4. Deforestation will ending our life and environment. Think, what, we can do to preserve our forests.

Forests: Our Lifeline Text Book Exercises

Question 1.
Explain how animals dwelling in the forest help it grow and regenerate?
Answer:
Animals help in growing and regenerating forests in many ways. Animals help in dispersing, seeds of certain plants. The decaying animal dung also provides nutrients to the seedling to plant. By this number of plants are growing which serve as a food for a number of herbivorous animals.

Herbivorous helps the carnivores to grow as they serve as food for them. So, the flora and fauna grows in the forests. Also, the animals work as the cleaning agents in the forest micro – organisms work on the death bodies of plants and animals and regenerate them.

Question 2.
Explain how forest prevent floods?
Answer:
If trees or widely we can say that forests are not present, rain will directly hit the ground and may cause the flood the area around it. Also, the heavy rain may damage the soil. Roots of trees and grasses basically bind the soil together, but in the absence of soil, they will be washed away or eroded.

The washed soil will get deposited in river and thus reduce the water carrying capacity of rivers. Which is the major causes of flood. Also, forests can absorb a lot of water. This also helps in preventing floods.

Question 3.
What are decomposers? Name any two of them. What do they do in the forest?
Answer:
The micro – organisms which convert the dead plants and animals to humus are known as decomposers. These micro – organisms play an important role in the forest. The any two decomposers are grubs and beetles. They clean the forests of the decaying dead bodies and replenishes the nutrient back to the forest soil.

Question 4.
Explain the role of forest in maintaining the balance between oxygen and carbon – dioxide in the atmosphere?
Answer:
Plants release oxygen through the C0₂ photosynthesis. The Plants help to provide oxygen for animal respiration. They also maintain the balance of oxygen and carbon dioxide in the atmosphere. That is why forests are called lungs.

Question 5.
Explain why there is no waste in a forest?
Answer:
The decomposers decompose the dead organisms. The decomposed matter is absorbed by plants as nutrients. Thus, there is no waste in a forest.

Question 6.
List five products we get from forests?
Answer:
We get following products from forests:

1. Medicine
2. Spice
3. Wood
4. Honey.
5. Gum

Question 7.
Fill in the blanks:

1. The insects, butterflies, honeybees and birds help flowering plants in ………………………..
2. A forest is a purifier of ……………………………. and …………………………
3. Herbs form the ……………………………… layer in the forest.
4. The decaying leaves and animal droppings in a forest enrich the ………………………….

Answer:

1. Pollination
2. Water, air
3. Lowest
4. Humus.

Question 8.
Why should we worry about the conditions and issues related to forests far from us?
Answer:
We should be worried about deforestation, as it would lead to floods, increase in earth’s temperature, depriving animals of their habitats and soil erosion.

Question 9.
Explain why there is a need of variety of animals and plants in a forest?
Answer:
Variety of animals are necessary for their survival and maintenance of food chain. For example, grass is eaten by insects, which in turn, are eaten by the frog. The frog is consumed by snakes and snakes is eaten by eagles.

Thus, it forms a food chain. There are so many food chains in the forest. All of these are linked. If any one food chain is disturbed, it affects other food chains. Also, animals convert the death plants and animals into humus and increase the fertility of soil.

Question 10.
In figure, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels: clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil roots, water table?
Answer:

Question 11.
Which of the following is not a forest product?

1. Gum
2. Plywood
3. Sealing wax
4. Kerosene

Answer:
4. Kerosene.

Question 12.
Which of the following statements is not correct?

1. Forests protect the soil from erosion.
2. Plants and animals in a forest are not dependent on one another.
3. Forests influence the climate and water cycle.
4. Soil helps forests to grow and regenerate.

Answer:
2. Plants and animals in a forest are not dependent on one another.

Question 13.
Micro – organisms act upon the dead plants to produce?

1. Sand
2. Mushrooms
3. Humus
4. wood.

Answer:
3. humus.

Extended Learning – Activities and Projects

Question 1.
The Department of Environment is to decide whether some portion of a forest in your area could be cleared for a housing complex. Write a letter to the department explaining your point of view as a concerned citizen?
Answer:
Do yourself.

Question 2.
Visit a forest? Here is a list of points that would make your visit more fruitful?

1. Make sure that you have permission to go into the forest.
2. Make sure that you can find your way around. Get a map and go along with some one who is familiar with the area.
3. Keep a record of the things you see and do. Observations make the visit interesting. Sketches and photographs are useful.
4. You may record bird calls.
5. Collect different kinds of seeds or hard fruits like nuts.
6. Try to recognise various types of trees, shrubs, herbs, etc. Make lists of plants from different places in the forest and of different layers. You may not be able to name all the plants, but it is worth recording and seeing where they grow. Make a record of approximate heights of plants, crown shape, bark texture, leaf size, and flower colour.
7. Learn to recognise the animal’s droppings.
8. Interview the forest officials and the people of surrounding villages and other visitors.
9. You must never collect birds eggs, and their nests should never be disturbed.

Answer:
Do yourself.

Forests: Our Lifeline Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (a)
Plants give out during photosynthesis?
(a) carbon dioxide
(b) oxygen
(c) humus
(d) none of these.
Answer:
(b) oxygen

Question (b)
Interdependence of animals for food is called –
(a) food – order
(b) food – cycle
(c) food – chain
(d) none of these.
Answer:
(c) food – chain

Question (c)
Small trees and grass and shrubs from the –
Answer:
(a) Canopy
(b) Under stories
(c) Lowest canopy
(d) All of these
Answer:
(b) Under stories

Question (d)
Deforestation leads to
(a) Soil erosion
(b) Floods
(c) Both of these
(d) None of these
Answer:
(c) Both of these

Question 2.
Fill in the blanks:

1. The branch part of a tree above the stem is known as the ……………………… of the tree.
2. The micro – organisms which convert the dead plants and animals to humus are known as …………………………
3. The plants help to provide ………………………….. for animal respiration.
4. The plants maintain the balance of oxygen and carbon dioxide in the …………………………
5. The covered ground with decaying material acts like a ……………………………
6. The root system helps water to seep down in the ……………………………
7. Forests protect the soil from ………………………..
8. Forests are the lifeline for the forest dwelling …………………………….

Answer:

1. Crown
2. Decomposers
3. Oxygen
4. Atmosphere
5. Sponge
6. Ground
7. Erosion
8. Communities.

Question 3.
Which of the following statements are true (T) or false (F):

1. Forests cause rain on the earth.
2. In a forests, the herbs form the lowest layer of the vegetation.
3. The various components of the forest are not interdependent on one another.
4. The forests keeps on growing and changing, and can regenerate.
5. Soils helps forests to grow and regenerate.
6. Forests influence climate, water – cycle and air quality.
7. Forests is a renewable natural resources.

Answer:

1. True
2. Ture
3. False
4. True
5. True
6. True
7. True.

Forests: Our Lifeline Very Short Answer Type Questions

Question 1.
What do you mean by forest?
Answer:
Forest is a place hosting a number of animals and plants.

Question 2.
Name any two trees in forest?
Answer:
Sheesham, Neem.

Question 3.
Write any three things we get from forests?
Answer:
Gum, medicine and wood.

Question 4.
Which plants constitute canopy in forests?
Answer:
Tall and giant trees.

Question 5.
What is the basic unit of any food chain?
Answer:
Plants.

Question 6.
Write one food chain in forest?
Answer:
Grass → Insects → Frog → Snake → Eagle

Question 7.
How is forest environment?
Answer:
Forest environment is peaceful and a cool breeze is blowing.

Question 8.
Name some animals that live deep inside forest?
Answer:
Bison, Jackals, Boar, Elephants.

Question 9.
What is humus?
Answer:
Humus is a dark coloured substance which is formed from the dead bodies of plants and animals.

Question 10.
What happens if an animal dies in the forest?
Answer:
The dead animals become food for vultures, jackals, insects and crows.

Question 11.
How does forest help in preventing floods?
Answer:
Forests absorb the rain .water in the soil and prevent the floods.

Question 12.
What is seed dispersal?
Answer:
The method by which plants scatter their seeds to reduce competition between off springs.

Question 13.
Define soil erosion?
Answer:
The weaving away of the soil by wind or water.

Question 14.
What do you mean by canopy?
Answer:
The branches of the tall trees look like a roof over the other plants in the forest is called canopy.

Question 15.
Define crown?
Answer:
Branch part of a tree above the stem is known as the crown.

Question 16.
What is deforestation?
Answer:
Cutting and destroying the forest is called deforestation.

Question 17.
What are the effects of deforestation?
Answer:
Floods, rising temperature, scarcity of flood and wood and disturbed flood chains are the results of deforestation.

Question 18.
What do you mean by afforestation?
Answer:
Planting more trees is called afforestation.

Question 19.
What would happen if it rains heavily in your town?
Answer:
There will be water logging or even flood. Everything will be in a mesh. No food, no water. No place, no stay.

Forests: Our Lifeline Short Answer Type Questions

Question 1.
Define soil erosion?
Answer:
Removal of fertile top layers of earth (soil) is called soil erosion. The soil erosion can be brought about by various agents like – water, wind, glaciers and ocean waves. Erosion occurs in both wet and arid regions. The various human activities like falling of trees, over – cropping and improper tilling accelerate soil erosion. The soil erosion can lead to floods.

Question 2.
What are the major factors that lead to soil erosion? Name them?
Answer:
The major factors that lead to soil erosion are the following:

1. Overgrazing by livestock
2. Deforestation
3. Over cultivation
4. Poor irrigation facilities
5. Water logging
6. Shifting cultivation.

Question 3.
Write about the dependence of animals on plants?
Answer:
Dependence of Animals on Plants:

1. Plants produce food by the process of photosynthesis and animals depend directly or indirectly on them for food.
2. Plants produce oxygen during photosynthesis and animals use this oxygen for respiration.
3. Plants act as habitat for the animals dwelling on trees.

Question 4.
Write about the dependence of plants on animals?
Answer:
Dependence of Plants on Animals:

1. Animals produce carbon dioxide during respiration which is released in the atmosphere. Plants use this oxygen for preparing food.
2. A number of insects, birds and bats help in pollination.
3. Some animals help in dispersal of fruits and seeds.

Question 5.
How forests help in bringing rain?
Answer:
Trees absorbs water from the soil through their roots. They then release the excess of water through the process of transpiration in the form of water vapours. These water vapours form clouds and clouds bring rain.

Question 6.
How are forests useful to us?
Answer:
The forests are very useful to us for the following reasons:

1. They conserve soil and water.
2. They are helpful in causing rains.
3. They give us food and fruit.
4. They are the natural habitats of animals.
5. They help in the maintenance of ecological balance.

Question 7.
Write a short note on deforestation?
Answer:
Deforestation is another important cause which brings about soil erosion. Deforestation leads to depletion of water vapour in the atmosphere so which in turn adversely affects the formation of rain bearing clouds and consequently the rainfall. In the absence of adequate rainfall, the soil dries up and its nutrient value is affected.

The decrease in rainfall affects the growth of plants and trees, thus leads to the formation of deserts. When there is no plant cover over the earth, it becomes naked. When rain falls over this naked earth, the water does not percolate down the earth and washes away. Similarly, strong winds also take away the top soil, thus causing soil erosion.

Question 8.
In which layer of the soil would you find humus? What is its importance to the soil?
Answer:
Humus is found in the top of layer of soil. The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil. From there, these nutrients are again absorbed by the roots of the living plants.

Forests: Our Lifeline Long Answer Type Questions

Question 1.
How we can conserved the forests?
Answer:

1. Unplanned and indiscriminate deforestation must be stopped.
2. Forest should not be over – exploited.
3. Use of wood as fuel should be discouraged.
4. Plant new fast growing trees.
5. Protect forest from fires, insects and diseases.
6. Protect national parks, wildlife sanctuaries or biosphere reserves.
7. Follow the guidelines of international organizations like W.W.F. and UNESCO for forest conservation.

Question 2.
Write the uses of forests?
Answer:
Forests are useful to us for the following reasons:

1. Forests provide timber for building and furniture.
2. Forests keep the environment cool and increase the chances of rainfall.
3. The roots of the trees hold the soil firmly thereby checking soil erosion.
4. Forests provide habitat to a variety of wild plants and animals.
5. The plants of forests use CO₂ and release oxygen in photosynthesis, thereby maintaining balance of gases in atmosphere.
6. Forests provide animal products such as honey, lac, wax, etc.
7. Forests provide plant products such as fruits, nuts, gums, resins, fibres, medicines, essential oil (like sandal wood), etc.
8. They are involved in the absorption of water which percolates in the soil, thereby becoming a part of the groundwater.

Question 3.
What will happen if forests disappear?
Answer:

1. Soil erosion will increase which will affect soil fertility and productivity.
2. Air pollution will increase which will ultimately threaten thirty existence of life on the Earth.
3. Unpredictable changes will take place in weather and climate.
4. Reduction in rainfall.
5. Reduction in recharging of existing water resources
6. Wildlife may also disappear along with forest.
7. Shortage of forest products.
8. Disturbance in ecological balance.
9. Increase in temperature
10. Global warming may reach in flooding of low lying area.

Question 4.
Draw a figure to show the difference between canopy and under stories?
Answer:

Question 5.
Draw a figure to show in the dependence of plant, soil and decomposers in a forest?
Answer:

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 16 Water: A Precious Resource

Activities

Activity – 1
Given here is the rainfall map of India (Fig.) It gives the average annual rainfall in different regions of our country?

Question 1.
Are you blessed with sufficient rainfall?
Answer:
No.

Question 2.
Is there sufficient water available in your area throughout the year?
Answer:
Yes.

Question 3.
Can we attribute this to mismanagement of water resources?
Answer:
Yes.

Water: A Precious Resource Text Book Exercises

Question 1.
Mark T if the statement is true and F if it is false:

1. The freshwater stored in the ground is much more than that present in the rivers and lakes of the world.
2. Water shortage is a problem faced only by people living in rural areas.
3. Water from rivers is the only source for irrigation in the fields.
4. Rain is the ultimate source of water.

Answer:

1. True
2. False
3. False
4. True

Question 2.
Explain how groundwater is recharged?
Answer:
The ground water get recharged through the process of infiltration. The infiltration means seeping in water from rain, rivers and lakes into the empty spaces and crack deep below the ground.

Question 3.
There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?
Answer:
The effect on the water table depends on the replenishment of the underground water. As only five families will share a tubewell, the water used for daily domestic purpose will not effect the water table as such. But if there is acute shortage of rains the water used by the families will not replenished and water table will fall down.

Question 4.
You have been asked to maintain a garden. How will you minimise the use of water?
Answer:
By collecting rain water. Also to minimise the wastage of water we will use the new technique of drip irrigation, which directly throws water at the base of plants.

Question 5.
Explain the factors responsible for the depletion of water table?
Answer:
Increasing population:
Increasing population creates demand for construction of houses, shops, offices, roads and pavements. This decreases the open areas like parks, and playgrounds. This, in turn, decreases the seepage of rainwater into the ground. What could be the consequence? Recall that a pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

Moreover a huge amount of water is required for construction work. Often groundwater is used for this purpose. So, on the one hand we are consuming more groundwater, and on the other we are allowing lesser water to seep into the ground. This results in depletion of water table. In fact, the water table in some parts of many cities has gone down to alarmingly low levels.

Increasing industries:
Water is used by all the industries. Almost everything that we use needs water somewhere in its production process. The number of industries is increasing continuously. Water used by most of the industries is drawn from the ground.

Agricultural activities:
A majority of farmers in India depend upon rains for irrigating their crops. Irrigation systems such as canals are there only in a few places. Even these systems may suffer from lack of water due to erratic rainfall. Therefore, farmers have to use groundwater for irrigation. Population pressure on agriculture forces increasing use of groundwater day by day. This results in depletion of water table.

Question 6.
Fill in the blanks with the appropriate answers:

1. The water bearing layer of the earth is …………………………
2. The process of water seepage into the ground is called ………………………
3. The water bearing layer of the earth is ………………………
4. The process of water seepage into the ground is called ………………………….

Answer:

1. Well and handpumps
2. Solid (ice), liquid (water), gas (water vapour)
3. Aquifer
4. Infiltration.

Question 7.
Which one of the following is not responsible for water shortage?

1. Rapid growth of industries
2. Increasing population
3. Heavy rainfall
4. Mismanagement of water resources.

Answer:
3. Heavy rainfall.

Question 8.
Choose the correct option. The total water –

1. In the lakes and rivers of the world remains constant.
2. Under the ground remains constant.
3. In the seas and oceans of the world remains constant.
4. Of the world remains constant.

Answer:
3. In the seas and oceans of the world remains constant.

Question 9.
Make a sketch showing groundwater and water table? Lab T it?
Answer:

Extended Learning Activities and Projects

Question 1.
Role play?
You are a water detective in your school? You have a term of six members? Survey the campus and make a note of the following:

1. Total number of taps
2. Number of taps leaking
3. Amount of water wasted due to leakage
4. Reasons of leakage
5. Corrective measures taken.

Answer:
Do yourself.

Question 2.
Groundwater pumped out?
Try to find out if there are any hand pumps in your neighborhood. Go to the owner or the users of a few of these and find out the depth at which they struck water? If there are any differences/think of the probable reason? Write a brief report and discuss it in your class. If possible, visit a place water boring is going on to install a hand pump? Watch the process carefully and find out the depth of the water table at that place?
Answer:
Do yourself.

Question 3.
Catching rainwater – Traditional methods? Form groups of 4 to 5 students in the class and prepare a report on the various traditional ways of water harvesting. If possible, use the following web link: www.rainwaterharvesting.org.?
Answer:
Do yourself.

Question 4.
Conservation of water? Carry out a campaign to conserve water at home and in the school. Design posters to remind others of the importance of water resources?
Answer:
Do yourself.

Question 5.
Create a logo? Hold a competition to create a logo or a symbol depicting water scarcity?
Answer:
Do yourself.

Water: A Precious Resource Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (a)
…………………………. is celebrated as the “world water day”?
(a) 22 March
(b) 20 March
(c) 22 April
(d) 20 April.
Answer:
(a) 22 March

Question (b)
Water is a Unique substance because?
(a) It is consumable
(b) It is colourless
(c) It exits in all three states
(d) Both (a) and (b)
Answer:
(c) It exits in all three states

Question (c)
Year …………………….. was observed as the International Year of fresh water to make people aware of this dwindling natural resource?
(a) 2002
(b) 2003
(c) 2004
(d) 2005.
Answer:
(b) 2003

Question (d)
The earth’s surface is covered with water about?
(a) 70%
(b) 71%
(c) 72%
(d) 73%.
Answer:
(b) 71%

Question (e)
Main source of water on earth is –
(a) rain
(b) snow
(c) glaciers
(d) all the above.
Answer:
(a) rain

Question (f)
One of these is not a source of surface water –
(a) lake
(b) rain
(c) river
(d) spring.
Answer:
(d) spring.

Question (g)
This is level …………………. of ground water?
(a) sea level
(b) rain
(c) aquifer
(d) (b) and (c).
Answer:
(d) (b) and (c).

Question (h)
Water has maximum density at –
(a) 0°C
(b) 4°C
(c) 98.4°C
(d) 100°C.
Answer:
(b) 4°C

Question (i)
Water is –
(a) a mixture
(b) a compound
(c) an element
(d) none of these.
Answer:
(b) a compound

Question (j)
The purest form of natural water is –
(a) river
(b) sea
(c) rain
(d) spring.
Answer:
(c) rain

Question (k)
Common salt content of sea water is –
(a) 1.5%
(b) 2.5%
(c) 3.5%
(d) 10%.
Answer:
(b) 2.5%

Question 2.
Fill in the blanks:

1. The amount of water recommended by the United Nations for drinking, cooking, washing and maintaining proper hygiene is a minimum of ……………………… liters per person per day.
2. The water that is fit for use is ………………………..
3. Solid form of …………………. water, and …………… , is present as ice caps at the poles of the earth.
4. ……………………. water is present in lakes, oceans, rivers and even underground.
5. The process of seeping of water into ground is called ………………………..
6. Water in the aquifiers can be usually pumped out with the help of …………………………. or ………………………..
7. Increase in population, industrial and agricultural activities are some common factors affecting ……………………….. table.
8. The rain water can be used to recharge the …………………………
9. Bhujpur in the Kutch area of ………………….. has a very erratic rainfall.
10. ……………………… irrigation is a technique of watering plants.

Answer:

1. 50
2. Fresh water
3. Snow, ice
4. Liquid
5. Infiltration
6. Tubewells, handpumps
7. Water
8. Groundwater
9. Gujarat
10. Drip.

Question 3.
Which of the following statements are true (T) or false(F):

1. Water is essential for all living beings.
2. Water exists in three forms.
3. There is an uneven distribution of water.
4. Water shortage has become a matter of concern throughout the world.
5. The gaseous form is the water vapour present in the air around us.
6. Many villages do not have water supply system.
7. The water – table does not varies from place to place.
8. Water drawn from under the ground gets replenished by seepage of rain water.
9. Rainwater harvesting is not necessary.
10. Rajasthan is a hot and dry place.
11. Water allows sunlight to pass through it.
12. Pure water has no taste.

Answer:

1. True
2. True
3. True
4. True
5. True
6. True
7. False
8. True
9. False
10. True
11. True
12. True.

Water: A Precious Resource Very short Answer Type Questions

Question 1.
What is the most important property of water?
Answer:
The most important property of water is its ability to dissolve various substances. Hence, it is called a universal solvent.

Question 2.
What are the sources of water?
Answer:
The two main sources of natural water are surface water and underground water or subsoil water.

Question 3.
What are the different states of water?
Answer:
The different states of water are solid, liquid and gas.

Question 4.
What are the characteristics of pure water?
Answer:
The pure water is colourless, odourless, tasteless and transparent.

Question 5.
What do you mean by a resource?
Answer:
Materials that we get from the environment to meet our needs are called resources.

Question 6.
A part from water, what are the other natural resources?
Answer:
A part from water, air, forests, minerals and fossilfuels are natural resources.

Question 7.
What is the percentage of water that is available for human beings?
Answer:
Only a tiny fraction about 0.01% of total water is used by human beings.

Question 8.
List the sources of water for your daily use?
Answer:
Sources of water for our daily use are well, lakes, rivers and ponds.

Question 9.
Define saturated solution?
Answer:
A saturated solution of a solute at a given temperature is a solution which contains as much of the solute as it can dissolve at that temperature.

Question 10.
Define unsaturated solution?
Answer:
If a solution contains less of the solute than what it can dissolve at that temperature, then it is called all unsituated  solution.

Question 11.
Name three forms of water?
Answer:
Three forms of water are solid, gaseous and liquid.

Question 12.
Which is universal solvent?
Answer:
Water.

Question 13.
What is the percentage of water (by weight) that an average elephant body has?
Answer:
An average elephant body has 80% water by weight.

Question 14.
If you have sample of tap water, well water and sea water, which do you think has the highest amount of salts?
Answer:
Sea water has highest amount of salts.

Question 15.
List the salts that can be obtained from the sea?
Answer:

1. Common salt (NaCl)
2. Sodium bromide (NaBr)
3. Potassium iodide (Kl)
4. Calcium salts.

Question 16.
Which sea has the highest salinity?
Answer:
Dead sea has the highest salinity.

Question 17.
Name two gaseous fuels which are prepared from water?
Answer:
Water gas and hydrogen gas.

Question 18.
Define water table?
Answer:
The depth at which water is found at a particular place is called water table.

Question 19.
What is Bawri?
Answer:
Bawri is a traditional way of collecting water.

Question 20.
What is potable water?
Answer:
The water which is fit for drinking is called potable water.

Question 21.
Define salinity of water?
Answer:
Water which has salts dissolved in it and is salty in taste is called salinity of water.

Question 22.
Define water cycle?
Answer:
The water from the earth reaches the atmosphere and from there it ultimately comes back to land, this is known as water cycle.

Question 23.
How does water cycle help in maintaining global climate?
Answer:
Liquid water on heating turns into water vapours. Water vapour on cooling again forms liquid water. This change of state of water over and over again makes the cycle in nature.

Question 24.
How are clouds formed?
Answer:
Water vapours being lighter and rise up in the atmosphere. At the upper layer of the atmosphere, where the temperature is lower. The vapours get condensed into tiny water droplets and clouds are formed.

Question 25.
Which unwanted material could be present in the water that you get from your local water supply?
Answer:
The unwanted materials in our water supply are dust particles, germs, bacteria and many other materials as impurities.

Question 26.
Define water harvesting?
Answer:
Most of the water that we get as rainfall just flows aways. This is a waste of precious natural resource. The rainwater can be used to recharge the groundwater. This is known as water harvesting or rainwater harvesting.

Question 27.
Define drip irrigation?
Answer:
Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant.

Water: A Precious Resource Short Answer Type Questions

Question 1.
Wrote a short note on source of water?
Answer:
Water is available to us through various sources. Rain water, lake Water, river water, sea water are some of the sources. Natural water from all these sources contain some impurities these are the dissolved minerals and salts. Apart from that, they contain some insoluble impurities too.

Question 2.
List the sources of water on the earth?
Answer:
There are two main sources of natural water:

1. Underground water
2. Surface water.
3. Underground Water: There are mainly two types of underground water –
   • (a) Well water
   • (b) Spring water.

2. Surface water:
It is of three types:

• Rain water
• River and lake water
• Sea water.

Question 3.
Write a short rote an river water?
Answer:
The river water is mainly due to rain or due to melting of snow on the mountains. The river water usually carries some suspended impurities and some soluble impurities. The soluble impurities are the dissolved salts and minerals. Apart from that they may carry certain micro – organisms and organic matter due to contamination.

Question 4.
Write a short note on sea water?
Answer:
Sea water is the largest source of natural water. But it is not fit either for drinking or for irrigation directly. This is because it contains a large number of dissolved salts of chlorides, bromides, iodides, sulphates and carbonates. The sea water is a rich source for common salt. It is recovered from sea water by evaporation and then is purified to remove the other impurities present.

Question 5.
Write a short note an underground water?
Answer:
Water present underneath the earth is tapped as it is an excellent source of pure drinking water. We usually dig wells. Depending on the geographical conditions of the place, the depth in which water is available is estimated. Well water contains some dissolved impurities.

Again the nature of the impurities depends on the geographical conditions. We also get water from springs under the earth. Such springs usually contain some dissolved mineral salts. However the spring water does not contain suspended impurities as it comes from deep under the earth.

Question 6.
Write a short note on rain water?
Answer:
It is the purest form of natural water available to us. Though the first few droplets of rain bring along with them some dust particles and micro-organisms, the later drops are free from impurities.

Question 7.
What are the properties of water?
Answer:
Properties of Water:

1. Pure water is colourless, odourless and tasteless.
2. Pure water freezes at 0 degree Celsius and boils at 100 degree celsius.
3. The density of water is 1 g/cc. It means that 1 cc of water at 1 degree Celsius weighs 1 gram.

Question 8.
What are the different ways by which water vapour is put into the atmosphere?
Answer:
The different ways by which water vapours put into atmosphere are as follows:

1. Factories and thermal stations produce a lot of steam and put is into the atmosphere.
2. Water in ponds, rivers and lakes, ocean gets evaporated due to atmospheric heat.
3. Plants throughout water vapours during respiration.

Question 9.
What makes the sea water so saline?
Answer:
Rivers flowing from different places bring water containing dissolved salts and minerals into the sea. Sea water is continuously evaporated by the heat of the sun. This evaporated water forms clouds and again fall on the earth as rain. This rain water again dissolves salts into it and goes into the sea. Thus the amount of salts in sea water goes on increasing.

Question 10.
How will you show that saline water is not fit for agriculture?
Answer:
Take two healthy plants of same type. Water both the plants separately one with ffesh water and other with saline water. Continue to water similarly for seven days and observe. The plant which was watered with saline water wilts. This shows that saline water is not fit for plants or agriculture.

Water: A Precious Resource Long Answer Type Questions

Question 1.
Draw a diagram to show water cycle?
Answer:

Question 2.
What are the causes of water scarcity?
Answer:
Causes of Water Scarcity:

1. Overpopulation
2. Over – irrigation for agriculture
3. Water pollution
4. Climatic change and variability
5. Indiscriminate cutting of forest
6. Increase in demand for water
7. Misuse of water
8. Poor water resource management
9. Disputes between the states for sharing water
10. Destruction of natural water reservoirs.

Question 3.
What are the methods to prevent water scarcity? Ans. Methods to prevent water scarcity:

1. Control population by adopting small family norms
2. Prevent misuse and wastage of water
3. Prevent water pollution
4. Replace large flush tanks with smaller ones.
5. Build dams, bunds and tanks to store rainwater.
6. Replace large flush tanks with smaller ones.
7. Recharge underground water
8. Recycle waste water for gardening
9. Follow drip irrigation or low water sprinklers for agriculture.

Question 4.
What are the effect of water scarcity on the life of people?
Answer:
Effect of water scarcity on the life of the people:

1. Long walk to fetch water.
2. Have to pay high price for buying water.
3. Low scope for generating employment.
4. Uncertainty over availability of water for agriculture.
5. Area will remain backward and neglected.
6. Increase incidents of crime.
7. More incidence of diseases due to poor sanitary conditions.
8. Fall in the productivity of animals.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 15 Light

Light Intex Questions

Question 1.
Paheli wants to know, what makes things visible to us? Boojho thinks that objects are visible only when light reflected from them reaches our eyes. Do you agree with him?
Answer:
Yes.

Question 2.
Boojho noted in his notebook: Is it not surprising that my image is of the same size as me whether the mirror is small or large?
Answer:
Yes.

Question 3.
Paheli made a note in her notebook: In a plane mirror the image is formed behind the mirror. It is erect, of the same size and is at the same distance from the mirror as the object is in front of it?
Answer:
Yes.

Question 4.
Boojho saw an ambulance on the road. He was surprised to see that the word ‘AMBULANCE’ in front was written in a strange manner?
Answer:
When the driver of a vehicle ahead of an ambulance looks in her/his rear view mirror, he/she can read ‘AMBULANCE’ written on it and give way to it. It is the duty of every one of us to allow an ambulance to pass without blocking its way.

Activities

Activity – 1
Write down the letters ABC on a piece of paper with sketch pen and look at its image in a plane mirror. Then find out which letters look the same as on the paper and which letters look different (fig.) Try to write these letters as seen in the mirror
Answer:

Activity – 2
Take a red book and allow white light to fall on it (fig)
Answer:
The color of the book is due to the red color which gets reflected from the book, i.e., it reflects only red color while it absorbs all the other colours of white light. A rose is red because it reflects only red light.

Light Text Book Exercises

Question 1.
Fill in the blanks:

1. An image that cannot be obtained on a screen is called ………………………..
2. Image formed by a convex ……………………….. is always virtual and smaller in size.
3. An image formed by a …………………….. mirror is always of the same size as that of the object.
4. An image which can be obtained on a screen is called a ………………………….. image.
5. An image formed by a concave ………………………. cannot be obtained on a screen.

Answer:

1. Virtual image
2. Mirror
3. Plane
4. Real
5. Lens

Question 3.
Match the items given in of Column I with one or more items Column II:

Answer:

1. (a) – (v)
2. (b) – (ii)
3. (c) – (i)
4. (d) – (iii)
5. (e) – (vi)

Question 4.
State the characteristics of the image formed by a plane mirror?
Answer:
The characteristics of the image formed by a plane mirror are:

1. It forms an erect image.
2. It forms a virtual image.
3. It forms the image behind the mirror.
4. The size of the image is same as that of the object.
5. It forms the image at the same distance behind the mirror as the object stands infront of it.

Question 5.
Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings?
Answer:
Letters like A, H, I, M, O, T, U, V, and W.

Question 6.
What is a virtual image? Give one situation where a virtual image is formed?
Answer:
The image which cannot be taken on a screen is called a virtual image. For example, when some object is placed very close to the concave mirror we do not get any image of that object on the white screen placed behind the mirror. This type of image is known as virtual image.

Question 7.
State two differences between a convex and a concave lens?
Answer:
Convex lens:

1. These are thick at middle and thin at edge.
2. They can form magnified image.

Concave lens:

1. These are thin at middle and thick at edge.
2. The image formed by these lens are always diminished in size.

Question 8.
Give one use each of a concave and convex mirror?
Answer:
Use of convex mirror:
It is used in vehicles as rear view mirror.

Concave mirror:
It is used by dentists to examine is used in vehicles as rear view mirror.

Question 9.
Which type of mirror can form a real image?
Answer:
Concave mirror.

Question 10.
Which type of lens forms always a virtual image?
Answer:
Concave lens.

Choose the correct option in questions 11 – 13:

Question 11.
A virtual image larger than the object can be produced by a –

1. Concave lens
2. Concave mirror
3. Convex mirror
4. Plane mirror

Answer:
2. concave mirror

Question 12.
David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be –

1. 3 m
2. 5 m
3. 6 m
4. 8 m.

Answer:
3. 6 m

Question 13.
The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be –

1. 1 m/s
2. 2 m/s
3. 4 m/s
4. 8 m/s.

Answer:
3. 4 m/s

Extended Learning – Activities and Projects

Question 1.
Play with mirror? Write your name with a sketch pen on a thin sheet of paper, polythene or glass. Read your name on the sheet while standing infront of a plane mirror. Now look at your image in the mirror?
Answer:
Do yourself

Question 2.
A burning candle in water? Take a shoe box, open on one side. Place a small lighted candle in it. Place a clear glass sheet Fig- Candle burning in water (roughly 25 cm x 25 cm) infront of this candle (Fig.). Try to locate the image of the candle behind the glass sheet. Place a glass of water at its position. Ask your friends to look at the image of the candle through the sheet of glass. Ensure that candle is not visible to your friends. Your friends will be surprised to see the candle burning in water. Try to explain the reason?
Answer:
Do yourself.

Question 3.
Make a rainbow?
Try to make your own rainbow. You can try this project in the morning or in the evening. Stand with your back towards the sun/ Take a hosepipe or a water pipe used in the garden. Make a fine spray in front of you. You can see different colours of rainbow in the spray?
Answer:
Do yourself.

Question 4.
Visit a laughing gallery in some science centre or a science park or a village mela. You will find some large mirrors there. You can see your distorted and funny images in these mirrors. Try to find out the kind of mirrors used there?
Answer:
Do yourself.

Question 5.
Visit a nearby hospital. You can also visit the clinic of an ENT specialist, or a dentist. Request the doctor to show you the mirrors used for examining ear, nose, throat and teeth. Can you recognise the kind of mirror used in these instruments?
Answer:
Do yourself.

Question 6.
Role play?
Here is a game that a group of children can play. One child will be chosen to act as object and another will act as the image of the object. The object and the image will sit opposite to each other. The object will make movements, such as raising a hand touching an ear, etc. The image will have to make the correct movement following the movement of the object. The rest of the group will watch the movements of the image. If the image fails to make the correct movement, she/he will be retired. Another child will take her/his place and the game will continue. A scoring scheme can be introduced. The group that scores the maximum will be declared the winner?
Answer:
Do yourself.

Light Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (a)
Formation of shadows suggests that light travels in –
(a) vacuum
(b) straight lines
(c) dark rooms
(d) None of these.
Answer:
(b) straight lines

Question (b)
A smooth polished surface which can return back the rays of light into the same medium is called –
(a) mirror
(b) lens
(c) prison
(d) None of these.
Answer:
(a) mirror

Question (c )
The phenomenon of bouncing back of the rays of light into the same medium is called –
(a) reflection
(b) refraction
(c) scattering
(d) None of these.
Answer:
(a) reflection

Question (d)
If the image cannot be taken on the screen, it must be –
(a) real
(b) virtual
(c) real or virtual
(d) None of these.
Answer:
(b) virtual

Question (e)
A spherical mirror with its reflecting surface on the outside is a –
(a) plane mirror
(b) convex mirror
(c) concave mirror
(d) None of these.
Answer:
(b) convex mirror

Question (f)
The mirror which is used as rear – view mirror in cars and scooters is, by nature –
(a) plane
(b) convex
(c) concave
(d) None of these.
Answer:
(b) convex

Question (g)
An image that can be obtained on a screen is –
(a) virtual
(b) real
(c) both real and virtual
(d) None of these.
Answer:
(b) real

Question (h)
The image produced by a plane mirror is –
(a) small
(b) real
(c) inverted
(d) equal size virtual and erect.
Answer:
(d) equal size virtual and erect.

Question (i)
In the formation of rainbow the altitude of the sun should be between or less than –
(a) 40° to 42°
(b) 42° to 44°
(c) 41° to 43°
(d) 0° to 40°.
Answer:
(a) 40° to 42°

Question (j)
White light comprises of ……………………… colours?
(a) 7
(b) 5
(c) 3
(d) 8.
Answer:
(a) 7

Question (k)
Which of the following can be used to prove that light consists of seven colours?
(a) plane mirror
(b) convex lens
(c) Newton’s disc
(d) None of these.
Answer:
(c) Newton’s disc

Question (l)
If the speed of rotation of Newton’s colour disc is fast enough, the various colours would blend and produce –
(a) white light
(b) red light
(c) no light at all
(d) green light.
Answer:
(a) white light

Question (m)
Primary colours are –
(a) red, blue, yellow
(b) red, yellow, magenta
(c) red, blue, green
(d) None of these.
Answer:
(c) red, blue, green

Question (n)
Which color is produced by mixing of blue and green?
(a) cyan
(b) magenta
(c) yellow
(d) blue.
Answer:
(a) cyan

Question 2.
Fill in the blanks:

1. The surface of water can act like a mirror and change the path of …………………………
2. An image formed by a plane mirror is erect and of the same size as the ……………………
3. The curved shining surface of a spoon acts as a ……………………
4. The inner surface of the cut ball is called and the outer surface is called ………………………
5. Concave mirrors are also used by dentists to see an enlarged image of the ………………………
6. The reflectors of tourches, headlights of cars and scooters are ……………………….. in shape.
7. The magnifying glass is actually a type of a ……………………………..
8. A convex lens is also called ………………………….. lens.
9. A concave lens is also called ……………………….. lens.
10. The rainbow has ………………………… colours.
11. The process of splitting up of white light into different colours is called ……………………
12. In a common rainbow the …………………………. colour is observed in the inner fringe and ………………………. on the outer fringe.

Answer:

1. Light
2. Object
3. Mirror
4. Concave, convex
5. Teeth
6. Concave
7. Lens
8. Converging
9. Diverging
10. Seven
11. Dispersion of light
12. Violet, red.

Question 3.
Which of the following statements are true (T) or false (F):

1. A shining stainless steel’spoon or plate can change the direction of light.
2. In a plane mirror only sides are interchanged.
3. The common example of a curved mirror is a spherical mirror.
4. The reflecting surface of the bell is convex.
5. Convex mirrors can form images of objects spread over a large area.
6. The lenses are not transparent.
7. A concave lens always forms erect, virtual and smaller image than the object.
8. A rainbow is seen as a large arc in the sky with many colours.
9. The sunlight consists of five colours.
10. The white light is composed of seven colours.

Answer:

1. True
2. Ture
3. True
4. True
5. True
6. False
7. True
8. True
9. False
10. True

Light Very Short Answer Type Questions

Question 1.
Give the names of four different sources of light?
Answer:
The four different sources of light are:

1. Sun
2. Stars
3. Moon
4. Firefly.

Question 2.
How does light travel from one point to the other?
Answer:
Light travel from one point to the other in straight line.

Question 3.
How can we change the direction of the light?
Answer:
We can change the direction of light by the phenomenon called reflection.

Question 4.
What is refraction?
Answer:
Bending of light when it travels from one medium to another is called refraction.

Question 5.
Define concave mirror?
Answer:
In a spherical mirror, of the reflecting surface is on the inside, it is called a concave mirror.

Question 6.
Define convex mirror?
Answer:
In a spherical mirror, if the reflecting surface is on the outside, it is called a convex mirror.

Question 7.
Define reflection of light?
Answer:
The phenomenon of turning back of light into the same medium on striking a polished surface is called reflection of light.

Question 8.
Define real image?
Answer:
An image that can be captured on a screen is called a real image.

Question 9.
Define virtual image?
Answer:
An image which cannot be captured on a screen is called a virtual image.

Question 10.
Define plane mirror?
Answer:
A plane polished surface capable of reflecting light regularly is known as a plane mirror.

Question 11.
How is the word AMBULANCE written on an ambulance?
Answer:

Question 12.
What happens when light falls on a mirror?
Answer:
The mirror reflects the direction of light that falls on it.

Question 13.
Why is the sky blue?
Answer:
The blue color of the sky is the result of the white light from the sun being separated into different colours.

Question 14.
Where do the different colours come from?
Answer:
All Colours came from light.

Question 15.
Define dispersion?
Answer:
The branching of white light into various colours is called dispersion of light.

Question 16.
How rainbows are formed?
Answer:
Rainbows are formed by sunlight falling on rain drops.

Question 17.
Have you ever seen a rainbow in the sky?
Answer:
Yes.

Question 18.
Does the white light consists of seven colours?
Answer:
Yes.

Light Short Answer Type Questions

Question 1.
Name the four features of the image formed by a plane mirror?
Answer:
The four features of the image formed by a plane mirror are:

1. The image formed by a plane mirror is as far behind the mirror as the object is in front of it.
2. It is virtual.
3. It is exactly of the same size and shape.
4. It is erect but laterally inverted.

Question 2.
What is the real image of an object?
Answer:
Real image is that image where the rays of light actually pass hence, it can be taken on the screen and is always inverted.
For example: image formed by pinhole camera, convex lens and concave mirror etc.

Question 3.
Name two situations in which the real image of an object is formed?
Answer:

1. When the object is at infinity.
2. When the object is at centre of curvature.

Question 4.
Give one use each Of concave and convex mirrors?
Answer:
Use of concave mirror:

1. They are used in reflected of car, head-lights and search lights.
2. They are used as shaving mirrors.
3. They are used in telescopes.

Use of convex mirrors:

1. They are used in automobiles by the drivers for seeing the erect images of the traffic.

Question 5.
What is virtual image? Give one example of virtual image?
Answer:
Virtual image is that image where the rays of light appear to intersect hence, it can only be seen, but it cannot be taken on the screen and is always erect. For example, image formed by plane mirror convex mirror and concave lens etc.

Question 6.
State two uses of concave mirror?
Answer:
The two uses of concave mirror are :

1. Concave mirrors are used as reflectors in car head-lights, search lights, torches and table lamps.
2. Concave mirrors are used by doctors to concentrate light on nose, ear, eyes etc.

Question 7.
Mention some of the uses of plane mirror?
Answer:
Uses of plane mirror are:

1. In hair cutting saloons, shops and at home.
2. For constructing periscope.
3. For constructing kelodoscope.

Question 8.
How will you come to know that the mirror given to you is a concave or convex?
Answer:
In the concave surface the polish is done on its outer surface and the inner surface is shining. If we bring it closer to our face the later will look very big. In a convex mirror the polish is done on the inner surface and then outer side is shining. In this mirror our face will always appear to be shorter.

Question 9.
Draw a ray diagram to explain the formation of a virtual image of a point source of light in a plane mirror?
Answer:
The image of a point object formed by a plane mirror.

Question 10.
In figure, complete the image of the coin after reflection at the surfaces of both the mirrors?

Fig. A ray diagram for formation of image by a pair of inclined mirrors.

Question 11.
Differentiate between real and virtual image formed by mirrors?
Answer:
Difference between real and virtual image:
Real image:

1. It can be obtained on a screen.
2. It is inverted.
3. It is obtained on the same side of mirror as the object.
4. Rays converge at a point to form the image.

Virtual image:

1. It cannot be obtained on a screen.
2. It is erect.
3. It is formed always behind the mirror.
4. Rays appear to diverge from a point where the image is formed.

Question 12.
Draw concave and convex mirrors?
Answer:

Question 13.
Draw convex and concave lens?
Answer:

Question 14.
Differentiate between reflection and refraction?
Answer:
Differences between reflection and refraction:
Reflection:

1. The speed of light remains the same.
2. The incident ray and the reflected ray travel in the same media.
3. In reflection the ray of light gets reflected back into the same medium.

Refraction:

1. The speed of light varies as it travels from one medium to another.
2. The incident ray and the refracted ray travel in different media.
3. In the refraction the ray of light bends at the surface of separation between the two media.

Question 15.
Define mixing of colours? What is the color of the object as the red and green glasses?
Answer:
When two colours mix or overlap, a third color is produced. Thus, red + green = yellow; red + blue = magenta; red + blue + green = white and so on. In fact, any color can be obtained by the combination of red, green and blue which are called the primary colours. The colours so produced. From them are called secondary colours. The mixing of colours can be shown with the help of the diagram given in fig.

Light Long Answer Type Questions

Question 1.
Explain the image formation in plane mirror?
Answer:
A mirror with a plane surface is called a plane mirror. The ordinary mirror we use is a plane mirror. Formation of image is one of effects on reflection of light. The image is seen behind the mirror and it is of the same size as the object. The distance from the object to the mirror and the distance between the mirror and the image are equal. In the plane mirror the right side of the object appears to be left side of the image, and the left side of the object appears to be the right side of the image. This inversion of sides is known as lateral inversion.

Question 2.
Define Newton’s experiment?
Answer:
Newton’s Experiment:
The idea that sunlight consists of several colours was first put forward by Sir Isaac Newton. He passed a narrow beam of light into a prism. The light that emerged from the prism was found to be coloured as in a rainbow. He gave the name spectrum to this coloured patch of light. The spectrum was seen to consist of seven colours of light – violet, indigo, blue, green, yellow, orange and red. The various colours found in white light can be easily remembered as VIBGYOR. The process of splitting up of white light into different colours is called dispersion of light.

Question 3.
Explain rainbow?
Answer:
Rainbows are formed by sunlight falling on rain drops. The rainbow is always observed with the back towards the sun. The rainbow is formed when rain drops owing to refraction and internal reflection produce deviation and dispersion into seven colours of the sunlight falling on them. The rainbows are visible only when the altitude of the sun is less than 42°.

A full rainbow can be seen from an aeroplane flying at higher altitudes. It is a matter of common observation that when one looks at a spray of water on which sun shines, rainbows are seen. When you look at the water falls with the sun shining at your back, a circular rainbow will be seen. In a common rainbow (primary rainbow) the violet color is observed in the inner fringe and red on the outer fringe.

Question 4.
How will you show that combining seven colours, we get white light?
Answer:
Take a circular cardboard disc of about 10 cm diameter. Divide this disc into seven segments. Paint the seven rainbow colours on these segments as shown in Fig. (a). A small hole is made at the center of the disc. Fix the disc loosely on the tip of a refill of a ball pen. Ensure that the disc rotates freely [Fig.(a)]. Rotate the disc in the daylight. When the disc is rotated fast, the colours get mixed together and the disc appears to be whitish [Fig. (b)]. This disc is popularly known as Newton’s disc.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 4 Heat

Heat Intext Questions

Question 1.
Boojho says, My left hand tells me that the water in mug C is hot and the right hand tells me that the same water is cold. What should I conclude?
Answer:
Both of the conclusions are true relative to each hand. But a single conclusion can not be drawn from the given information.

Question 2.
Boojho wondered which of the two scales shown in fig. he should read. Paheli told him that India has adopted the Celsius scale and we should read that scale. The other scale with the range 94-108 degrees is the Fahrenheit scales (°F). It was in use earlier.

Answer:
Yes

Question 3.
Boojho got a naughty idea. He wanted to measure the temperture of hot milk using a clinical thermometer. Paheli stopped him from doing so?
Answer:
Yes, do not use a clinical thermometer for measuring the temperature of any object other than he human body because it may break.

Question 4.
Boojho now understand why clinical thermometer can not be used to measure high temperatures. But still wonders whether a laboratory thermometer can be used to measure his body temperature?
Answer:
Yes, laboratory thermometer can also be used for measuring body temperature.

Question 5.
Boojho wonders why the level of mercury should change at all when the bulb of the thermometer is brought in contact with another object?
Answer:
The temperature of other object may not be the same as that of the bulb of the thermometer. When bulb is brought in contact with that object, the temperature of the bulb changes. Thus, the level of mercury also changes.

Question 6.
Paheli asks: “Does it mean that heat will not be transferred if the temperature of two objects is the same?”
Answer:
Yes.

Activities
Activity 1
Lost some objects you use commonly in given table. Mark these objects as cold or hot?
Answer:

Activity 2
Measure the body temperature of some of your friends (at least 10) with a clinical thermometer.
Answer:
Observation for body temperature of some persons.

Activity 3
Take a rod or flat strip of a metal, say of aluminium or iron. Fix a few small wax pieces on the rod. These pieces should be at nearly equal distances (fig.). Clamp the rod to a stand. If you do not find a stand, you can put one end of the rod in between bricks. Now, heat the other end of the rod and observe.

What happens to the wax pieces? Do these pieces begin to fall? Which piece fall the first? Do you think that heat is transferred from the end nearest to the flame to the other end?
Answer:
The wax pieces start to melt and fall down.
Yes.
The piece nearest to the flame tall first. Yes, heat is transferred from the end nearest to the flame to the other end.

Activity 4
Heat water in a small pan or a beaker. Collect some articles such as a steel spoon, plastic scale, pencil and divider. Dip one end of each of these articles in hot water (fig.). Wait for a few minutes. Touch the other end. Enter your observation in Table.

Activity 5
Explain with activity heat transfer by conduction method?
Answer:
1. Aim:
To understand, ‘heat transfer by conduction’.

2. Required material:
Iron stick, some nails, candle.

3. Process:
Attach the nails on thin iron rod at some intervals with help of candle-wax as shown in figure. Now heat one end of iron rod with candle.

4. Analysis:
When we Start heating one end of iron rod, nails start falling one by one. The nail which is adjacent to hot end of iron – rod, falls first and then other nails 1 fall in sequence. Falling of nails in sequence indicate heat flow by conduction. Some time later, heat reaches to other end of rod and entire rod becomes hot.

5. Conclusion:
Heat transfer in iron – rod takes place by conduction.

Activity 6
Take a round bottom flask (if flask is not available, a beaker can be used). Fill it two – thirds with water. Place it on a tripod, or make some arrangement to place the flask in such a way that you can heat it by placing a candle below it. Wait till the water in the flask in still. Place a crystal of potassium permanganate at the bottom of the flask gently using a straw. Now, heat the water by placing the candle just below the crystal. Write your observation in your notebook and also draw a picture of what you observe.
Answer:
When water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves

down towards the source of heat. This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is knwon as convection.

Heat Text book exercises

Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer?
Answer:
Similarities:

1. Both use mercury.
2. Both measure temperature.

Differences:
1. The range of a mercury thermometer is 100°C. A mercury thermometer having graduations from 0°C to 100°C while the temperature interval marked on the clinical thermometers ranges from 35°C to 43°C.

2. The temperature on laboratory thermometer falls by itself, but not so in clinical thermometer. In clinical thermometers, a jerk is given so that it is set again for measuring human body temperature.

Question 2.
Give two emamples each of conductors and insulators of heat?
Answer:
Conductors: Copper, Aluminium

Insulators: Wood, Plastic

Question 3.
Fill in the blanks:

1. The hotness of an object is determined by its ………………
2. Temperature of boiling water cannot be measured by a ………………. thermometer.
3. Temperature is measured in degree …………………
4. No medium is required for tansfer of heat by the process of ………………..
5. A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of …………………..
6. Clothes of ………………. dolours absorb heat better than clothes of light colours.

Answer:

1. Temperature
2. Clinical
3. Celsius
4. Radiation
5. Conduction
6. Dark/black.

Question 4.
Match the following:

Answer:

(i) (d)
(ii) (c)
(iii) (b)
(iv) (a)

Question 5.
Discusss why wearing more layers of clothing during winter keeps us warmer than waering just one thick piece of clothing?
Answer:
More layers of clothing keep us warm in winters as they have a lot of space between them. Air is a poor conductor of heat. This increases the insulation and thus, comfortability warm of the clothes as a whole.

Question 6.
Look at fig Mark where the heat is being transferred by conduction, by convection and by radiation?
Answer:

Question 7.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain?
Answer:
In places of hot climate it is advised that the outer wall of houses be painted white because white colour do not radiate heat easily.

Question 8.
One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

1. 80°C
2. More than 50°C but less than 80°C
3. 20°C
4. Between 30°C and 50°C

Answer:
4. Between 30°C and 50°C.

Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

1. Flows from iron ball to water.
2. Not flow from iron ball to water or from water to iron ball.
3. Flows from water to iron ball.
4. Increase the temperature of both.

Answer:
2. Not flow from iron ball to water or from water to iron ball.

Question 10.
A wooden spoon is dipped in a cup of ice cream. Its other end

1. Becomes cold by the process of conduction.
2. Becomes cold by the process of convection.
3. Becomes cold by the process of radiation.
4. Does not become cold.

Answer:
4. Does not become cold.

Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

1. Copper bottom makes the pan more durable
2. Such pans appear colourful
3. Copper is a better conductor of heat than the stainless steel
4. Copper is easier to clean than the stainless steel.

Answer:
3. Copper is a better conductor of heat than the stainless steel

Extended Learning – Activities and Projects

Question 1.
Go to a doctor or your nearest health centre. Observe the doctor taking temperature of patients Enquire?

1. Why she dips the thermometer in a liquid before use.
2. Why the thermomter is kept under the tongue.
3. Whether the body temperature can be measured by keeping the thermomter at some place other than the mouth.
4. Whether the temperature of different parts of the body is the same or different. You can add more questions which come to your mind.

Answer:

1. Because to prevent infection. This liquid is an antiseptic.
2. Because the temperature below the tongue represents actual temperature of body.
3. Yes, but not so desirable.
4. Temperature of different parts of the body are different.

Question 2.
Go to a veterinary doctor (a doctor who treats animals)?
Discuss and find out the normal temperature of domesitc animals and birds.
Answer:

Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation?
Answer:
No, the paper strip does not burn. Iron it a good conductor of heat. It takes away .the heat from paper and saves it from burning.

Question 4.
Take a sheet of paper. Draw a spiral on it as shown in the fig. Cut out the paper along the line. Suspend the paper as shown in figure, above a lighted candle. Observe what happens. Think of an explanation?

Answer:
The paper spiral keeps moving. This is so because the air above the flame moves up due to convection.

Question 5.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Answer:
Do with the help of your subject teacher.

Heat Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (i)
By which method heat transfer takes place in solids –
(a) Convection
(b) Conduction
(c) Radiation
(d) All three.
Answer:
(b) Conduction

Question (ii)
When can feel the hotness of some hot substance like electric iron from a little distance by which method?
(a) Convection
(b) Conduction
(c) Radiation
(d) All three methods.
Answer:
(c) Radiation

Question (iii)
By which method sun’s heat reaches to earth –
(a) Conduction
(b) Convection
(c) Radiation
(d) Conduction and convection.
Answer:
(c) Radiation

Question (iv)
The handle of cooker is make up of bakelite because it is –
(a) Cheap
(b) Looks beautiful
(c) Bad conductor of heat
(d) Good conductor of heat.
Answer:
(c) Bad conductor of heat

Question (v)
By which of the following processes the water circulates in radiator of the bus engine and keeps the engine cool –
(a) Convection
(b) Radiation
(c) Conduction
(b) Conduction and radiation.
Answer:
(a) Convection

Question (vi)
Ice is kept in four boxes made of the following materials. If the same quantity of ice is kept for same time in the boxes, in which box the ice will melt least –
(a) Lead
(b) Wood
(c) Steel
(d) Thermocoal.
Answer:
(d) Thermocoal.

Question (vii)
In radiation, heat energy travel in –
(a) Curred lines
(b) Zig – zag lines
(c) Straight lines
(d) None of these.
Answer:
(c) Straight lines

Question (viii)
A thermos flask prevents loss or gain of heat by –
(a) Radiation only
(b) Conduction only
(c) Convection only
(d) None of these.
Answer:
(b) Conduction only

Question 2.
Fill in the blanks:

1. The measure of …………… energy is temperature.
2. ……………. is the apparatus to measure temperature.
3. The temperature at which a substance changes its state from solid to liquid is called its …………….
4. In convection, water travels from …………. region to the ……………. region.
5. The black bodies are good ………….. of heat.
6. Water is a …………… conductor of heat.
7. Transfer of energy between different part of a body is called ……………
8. Shining bodies are poor ……………. of heat energy.
9. Dark objects absorbs …………… heat then light coloured object.

Answer:

1. Heat
2. Thermometer
3. Melting point
4. Hotter, colder
5. Absorber
6. Bad
7. Conduction
8. Radiators
9. More.

Which of the following statements are True (T) or False(F):

1. Heat is a form of energy.
2. Heat flows from a lower temperature to a higher temperature.
3. The temperature of a healthy adult is 98.4°C.
4. Iron is better conductor of heat than aluminium.
5. The temperature at which a substance changes its state from solid to liquid is called its melting point.
6. In thermometer highest points is 100°C.
7. In thermometer’s the lowest point is 273°K Radiation of heat can take place without a medium. See
8. breeze is the blowing of air from sea toward the land.
9. Air is a good conductor of heat.

Answer:

1. Ture (T)
2. False (F)
3. False (F)
4. False (F)
5. True (T)
6. Ture (T)
7. True (T)
8. True (T)
9. True (T)
10. False (F).

Question 4.
Match the items in Column A with Column B:

Answer:

(i) (d)
(ii) (a)
(iii) (b)
(iv) (c)

Heat Very Short Answer Type Questions

Question 1.
Define clinical thermometer?
Answer:
The thermometer that is used to measures our body temperature is called a clinical thermometer.

Question 2.
What is the range of a clinical thermometer?
Answer:
35°C to 42°C.

Question 3.
Why is range of a clinical thermometer is chosen to be 35°C to 42°C?
Answer:
The clinical thermometer is designed to measure the temperature of human body only. The temperature of human body normally does not go below 35°C or above 42°C. That is the reason why this thermometer has the range 35°C to 42°C.

Question 4.
What is the use of kink in thermometer?
Answer:
Kink prevents mercury level from falling on its own.

Question 5.
Why dose the mercury not fall or rise in a clinical thermometer when taken out of the month?
Answer:
The kink prevents the mercury level from falling down.

Question 6.
Name two substances which contract on heating.
Answer:
Bismuth, Ice.

Question 7.
Which substances has the highest heat capacity?
Answer:
Water.

Question 8.
Which gets hotter soon, land or water?
Answer:
Land.

Question 9.
What is thermos flask?
Answer:
Thermos flask is a device in which heat losses due to conduction, convention and radiation are minimised.

Question 10.
How does the heat travel in air? In which direction does the smoke go?
Answer:
Heat moves in air by convection. The smoke moves in the upward direction.

Question 11.
How does the heat from the sun reaches?
Answer:
By radiation.

Question 12.
Why are you advised to use an umbrella when you go out in the Sun?
Answer:
The umbrella protects us from heat rays of the Sun.

Question 13.
What is temperature?
Answer:
Temperature of an object is the degree of its hotnees. It tells us how hot or cold the object is.

Question 14.
Name the instrument we use to measure temperature.
Answer:
We use thermometers to measure the temperature.

Question 15.
Write the S.I. unit of heat?
Answer:
Joule.

Question 16.
Write the names of the methods of heat transfer?
Answer:
The names of methods of heat transfer are conduction, convection and radiation.

Question 17.
The iron nails from aluminium rods falls faster than from iron rod. What do you conclude from this statement?
Answer:
It means that aluminium is a better conductor of heat as compared to iron. So it passes heat much quickly to the iron nails and they fall down due to melting of wax.

Question 18.
Why in summer days does the fan give hot air first in a closed room when it is switched on?
Answer:
In a closed room the hot air remains at top because it is lighter. So when fan is turned on, it circulates the upper air first and it gives a current of hot air.

Question 19.
Why are the cooking utensile made up of metals?
Answer:
Cooking utensils are made up of metals as they are good conductor of heat. They transfer the heat to the food inside quickly and the food is cooked easily.

Question 20.
What are good conductors of heat? Give examples.
Answer:
Substances which allow the heat to pass through them are called good conductors of heat. Examples : all metal like iron, aluminium, copper and alloys like steel etc.

Question 21.
What are bad conductor of heat? Give examples.
Answer:
Substance which do not allow the heat to pass through them are called bad conductor of heat.
Examples: wood, paper, asbestos, rubber etc.

Question 22.
Why do fire workers wear bright clothes?
Answer:
Fire worker wears bright clothes because bright clothes are good reflector of heat. They send back the heat falling on them. Thus fire workers do not catch fire and heat easily.

Question 23.
On a cold winter night, why do we feel colder when the sky clear than when it is cloudy?
Answer:
As clouds are bad conductor of heat, they do not allow the warm air around us to flow up. So heat remains near the ground and we feel warmer.

Question 24.
When does the conduction of heat stop in two bodies in contact?
Answer:
The conduction of heat stops in two bodies in contact when the two bodies attain equal temperature. That is the two bodies have no temperature difference.

Question 25.
How do you note the temperature of the body with thermometer?
Answer:
When bulb of thermometer comes in contact with our body. The mercury in the thin tube rises up. When the temperature of thermometer and body becomes equal, the level of the mercury does not rise further. This is the temperature of the body.

Heat Short Answer Type Questions

Question 1.
What is the difference between heat and temperature?
Answer:
Heat:

1. Heat is a form of energy. It flows from a body at higher temperature to a body at lower temperature.
2. Heat is measured in Joules or Calorie.

Temperature:

1. Temperature is a measure of energy in the form of heat. Generally the temperature of a body increases when it is heated.
2. Temperature is measured in Celcius.

Question 2.
On basis of what properties, mercury is used in thermometer?
Answer:
Mercury is used in thermometer because of the following properties:

1. Thermal expansion is uniform in mercury.
2. As it is shining silvery white, its thermal expansion is seen easily. This helps in noting the reading of thermometer easily.
3. It does not stick to the surface of glass.
4. Mercury does not freeze at 0°C because it’s freezing point is 39°C.

It does not boil at 100°C because it’s boiling point is 357°C. Hence, mercury has wide range of temperature between its freezing point and boiling point.

Question 3.
Distinguish between conduction and convection.
Conduction:

1. In conduction the molecules do not leave their position.
2. It generally takes place in solid.

Convection:

1. In convection the molecules of the substance actually move from hotter region to colder region.
2. It generally takes place in gases and liquids.

Question 4.
Why should we wear dark coloured clothes in winter and light coloured clothes in summer?
Answer:
Bright clothes objects tend to reflect back the heat more, than to absorb the heat. Therefore, it is advisable to wear them in summer. On the other hand, dark coloured clothes have a greater tendency to absored and hence “retain” the heat. Hence they are worn in winter.

Question 5.
Why rise in temperature in two substances of equal quantity is not same even through equal amount of heat is given to them?
Answer:
The same quantity of heat supplied to the same amount of different substances, then the rise in teperature would not be same bacause the rise in temperature of the substance would depend on their specific heat. The temperaute of the substance which has less specific heat would rise more.

Question 6.
What are the precautions to be observed while reading a clinical thermometer?
Answer:
Precautions to be observed while reading a clinical thermometer are:

1. Thermometer should be washed before and after use, preferably with an antiseptic solution.
2. Ensure that before use, the mercury level is below 35°C.
3. Read the thermometer keeping the level of mercury along the line of sight.
4. Handle the thermometer with care. If it hits against some hard object, it can break.
5. Don’t hold the thermometer by the bulb while reading it.

Question 7.
What are the precautions to be observed while reading a laboratory thermometers?
Answer:
In addition to the precautions needed while reading a clinical thermometer, the laboratory thermometer

1. Should be kept upright not tilted.
2. Bulb should be surrounded from all sides by the substance of which the temperature is to be measured. The bulb should not touch the surface of the container.

Question 8.
Define mamixum – minimum thermometer.
Answer:
Different types of thermoters are used for different puroposes. The maximum and minimum temperatures of the previous day, reported in weather reports, are measured by a thermometer called the maximum – minimum thermometer.

Question 9.
Draw diagram of the laboratory thermometer. Mark the lower and upper fixed temperatures on a Celsius scale and indicate the values in Kelvin scale aslo.
Answer:

Question 10
Name three different types of thermometers. Which of these is most sensitive?
Answer:
The three different types of thermometers are:

1. Mercury thermometer
2. Alcohol thermometer
3. Gases thermometer.

Mercury thermometer is used to measure nominal temperature. Alcohol thermometer is used to measure very low temperature. The gaseous thermometer is the most sensitive of all, as the gases are very sensitive to the slightest temperature change. The gaseous thermometers are rarely used because of the difficulty they pose in handling.

Question 11.
Define digital thermometers with diagram?
Answer:
There is a lot of concern over the use of mercury in thermometers. Mercury is a toxic substance and is very difficult to dispose of if a thermometer breaks. These days, digital thermometers are available which do not use mercury.

Heat Long Answer Type Questions

Question 1.
Explain with experiment the method of heat transfer by radiation?
Answer:
To know that the amount of heat absorbed or radiated by a substance depends upon colour of a substance.

Required Material:
Two containers of same metal, two thermometer, black and white colour, two cardboard pieces.

Procedure:

1. Colour the outer surface of one container with black and other with white.

2. Add equal quantity of tap water in both and insert thermometer by making a hole at the centre of card board as shown in picture.

3. Keep both containers for about 30 minutes under the sun. Then note down the temperature of both the containers.

4. Now add same quantity of hot water heated upto 50 to 60°C in both containers. Arrange the card board and thermometer properly and keep both of them is shadow for about 10 minutes. Then note down temperature of water from both containers.

Analysis:

Position 1.
After keeping containers for 30 minutes under the sun, you will see that, there is more increase in temperature of water in black container in comparision with white one. It is because black or dark colours are good absorbers of heat while white (light) colour is not.

Position 2.
After keeping the containers for 10 minutes in shadow, you will see that water in black container has cooled more than the water in white container. It is because black or dark colours are good emitters of heat, while white (light) colours are not.

Conclusion:

1. Black or dark colour are good absorbers or emitters of heat.
2. White or light colurs are good reflectors of heat. It means they are not good absorbers or emitters of heat.
3. The amount of heat emitted or absorbed by a substance depends upon colour of a substance.

Question 2.
Write some facts which indicates that sun light reaches to us by method of radiation?
Answer:
Medium is required for transfer of heat by conduction and convection process. When you stand under the sun, you experience heat. Heat reaches upto us from the sun. It is necessary to know following facts:

1. Air is poor conductor of heat hence heat is not transfered by conduction method in air.

2. Sun’s heat does not reach upto us by convection process also. Beacuse, you know that, convection will start only after earth is heated.

3. There is vacuum between sun and errth i.e. there is no medium. Hence sun’s heat can not reach upto us by conduction or convection method because medium is required for both methods. It means that sun’s heat reached us by some other method called radiation.

Question 3.
How does the highest and lowest constant point of thermometer marked?
Answer:
Two constant points i.e., lowest and highest are required to be marked while graduating the thermometer.

The lowest constant point:
The thermometer bulb is kept in a melting ice as shown in figure. Mercury descends in tube and remains constant after some time. This point is marked. This is lowest constant point of thermometer.

Highest constant point:
The thermometer bulb is kept in vapour of pure boiling water. Mercury ascends in tube and remains constant after some time. This point is marked. This is the highest constant point of thermometer.

Celcius scale:
Lowest constant point (temperature of melting ice) is indicated by °C and highest constant point (temperature of boiling water) is indicated by 100°C in this scale. The length between these two point is divided into 100 equal parts. The value of each parts is 1°C.

Question 4.
How does sea breeze flow?
Answer:
Convection current has got an important role in change of seasons. Sea breeze is the best example of this principle. In fact during day time, seashore land gets hotter earlier than water. Air in contact with it, becomes hot and rises. (Density of hot air is less and hence it is lighter) and hence to take its place cold air above sea flows towards seashore. Because of it, during day time sea breeze flows.

During night time, this process gets reversed. See water becomes cool later than seashore during night time. (As the specific heat capacity of water is more than the seashore land, it takes longer time to become hot and also takes longer time to become cool). Hence during night time, temperature of sea is more than seashore. As a result surface air of sea gets hotter and rises and air above seashore takes its place. In this way during night time cool air flows towards sea.

Question 5.
What is thermometer? Describe its construction?
Answer:
A thermometer is a device which is used to measure temperature accurately. The two commonly used thermometers are clinical thermometer and laboratory thermometer. The clinical thermometer is used by doctors to measure the body temperature. The laboratory thermometer is used in laboratories to measure melting point and boiling points.

A thermometer consists of a very fine capillary glass tube attached to a bulb containing mercury. In laboratory  thermometer the mercury is at zero mark when placed in ice and is at hundred mark when placed in boiling water. Therefore, zero, mark is considered as lower fixed point and 100 mark is considered as upper fixed point (see fig.).

Question 6.
Explain the structure or thermos flask with neat diagram?
Answer:
Thermos Flask was prepared first of all by Sir James Debar. It is used for storing cold or hot liquids for hours together. It is designed in such a way that heat transfer by conduction, convection and radiation should be minimum.

MP Board Class 7th Science Solutions