Thursday, 7 July 2011

Water: A Precious Resource: Chapter 16 | Science |CBSE Class VII (7th) Exercises

Solutions :
1. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T)
(b) Water shortage is a problem faced only by people living in rural areas. (F)
(c) Water from rivers is the only source for irrigation in the fields. (F)
(d) Rain is the ultimate source of water. (T)



2. Explain how groundwater is recharged?
Answer :The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process.At places the groundwater is stored between layers of hard rock below the water table. This is known as an aquifer. Water in the aquifers can be usually pumped out with the help of tube wells or hand pumps.

3. There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?
Answer : Water drawn from under the ground gets replenished by seepage of rainwater. The water table does not get affected as long as we draw as much water as is replenished by natural processes. However, water table may go down if the water is not sufficiently replenished. As stated, there are ten tube wells in a lane of fifty houses,  so the quantity of water being pumped out by 10 tube wells can not be replenished by the available sources like  rain, drainage to recharge the ground water table. As a result of this, in long term the water table beneath will be get depleted and after some years there will be no water for 10 tube wells to pump out.

4. You have been asked to maintain a garden. How will you minimise the use of water?

Answer : For maintaining the garden, we can take following steps to minimise the use of water :
  1. We can employ drip irrigation to water the garden. Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant.
  2. We should water the plants in garden in early morning hours.If you are unable to water early in the morning, late afternoon is the next best; this is after the sun's heat has lost its harshness but before the chill in the air begins to set in.
  3. We should avoid using a sprinkler during windy weather, as the water will blow away and evaporate, wasting the water.

5. Explain the factors responsible for the depletion of water table.
Answer : The factors responsible for the depletion of water table :

1. 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.  A cemented  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

2.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.
3. 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.

6. Fill in the blanks with the appropriate answers:
(a) People obtain groundwater through tube wells and hand pumps.
(b) Three forms of water are solid, liquid and vapour.
(c) The water bearing layer of the earth is aquifer
(d) The process of water seepage into the ground is called infiltration.

7. Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries
(ii) Increasing population
(iii) Heavy rainfall
(iv) Mismanagement of water resources
Answer : (iii) Heavy rainfall

8. Choose the correct option. The total water
(i) in the lakes and rivers of the world remains constant.
(ii) under the ground remains constant.
(iii) in the seas and oceans of the world remains constant.
(iv) of the world remains constant.
Answer : (iv) of the world remains constant.

9. Make a sketch showing groundwater and water table. Label it.

Answer : 
Ground Water Table Recharge


Water: A Precious Resource: Chapter 16 | Science |CBSE Class VII (7th) Lesson Exercises
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Did you know?
The importance of water management has been highlighted by a watershed management project near the village of Kothapally. The project has yielded dramatic results. Groundwater levels have risen, green cover has increased, and productivity and incomes in this semi-arid region have dramatically improved.

6 comments:

  1. HI I AM A 7TH STANDARD BOY AND THNX FOR THIS LESSON CAUSE WE HAVE THE SAME TXT BOOK AND SAME LESSONS SO IT IS SO EASY FOR ME TO COVER THE NOTES AND EXERCISES FOR THESE WORKS IN MY SCHOOL THNX U ROCK NCERT BOOKS

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  2. please answer these questions:-
    1. the distance b/w the object and its image is 6m. if the object moves 1m towards the mirror then the distance b/w object and its image will be________m.
    2.the point where a concave mirror forms the image of a very distant object is the __________of the mirror.
    3.write true or false:-
    #~when we stand b/w a pair of plane mirrors , we see an infinite no. of images._____(T/F).
    #~motor vehicles generally use either a plane or convex mirror as the 'rear-view' mirror.______(T/F).

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  3. please reply the above given comment

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  4. hiiiiiiiii i am adarsh am a student of 7

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