Thursday, November 8, 2012

CBSE Class 7 - Science - CH16 - Water: A Precious Resource

Water: A Precious Resource
Save Water
credits:openclipart
NCERT Solutions, Q & A

Q1: When 'World Water Day' is celebrated?

Answer: March 22nd.

Q2: What is the main objective of celebrating 'Water Day'?

Answer: We celebrate water day every year to attract the attention of everybody towards the
importance of conserving water.

Q3: How much much amount of water is recommended by UN for daily use by a person?



Answer: The amount of water recommended by the United Nations for drinking, washing, cooking and maintaining proper hygiene is a minimum of 50 litres per person per day. This amount is about
two and a half buckets of water per person per day.

Q4: How much water in percentage is fit for human for consumption?

Answer: 0.006%

Q5(NCERT):  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/F)
(b) Water shortage is a problem faced only by people living in rural areas. (T/F)
(c) Water from rivers is the only source for irrigation in the fields. (T/F)
(d) Rain is the ultimate source of water. (T/F)

Answer:
(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (True ✓)

(b) Water shortage is a problem faced only by people living in rural areas. (False ✗)
Explanation: Water shortage problem is faced by both people living in rural and in urban areas.

(c) Water from rivers is the only source for irrigation in the fields. (False ✗)
Explanation: Rivers, Canals, Wells, Tubewells are main sources for irrigation.

(d) Rain is the ultimate source of water. (True ✓)
Explanation: Rainwater recharges underground water and refills ponds and lakes. That's why rainwater harvesting is recommended to address water scarcity issues.

Q6: In how many forms water exists in nature?

Answer:  In nature, water exists in three forms:
  1. Solid : it exists as icecaps at the poles, snow-covered mountains and glaciers.
  2. Liquid: it is in the form of water in oceans, lakes and rivers, and underground water.
  3. Gas: it is present as gas i.e. the water vapours in the air.
Q7: Draw a flow diagram showing processes that convert water into its different states.

Answer:
Three States of Water
Three States of Water


Q8: What is water table?

Answer: When we you dig a hole in the ground, we find moist soil at certain depth. Soon, on further digging we reach a depth at which all space between the soil particles and cracks in the rocks are filled with water. The upper limit of this depth is called the water table.

Q9: What is groundwater?

Answer:  The water found below the water table is called groundwater or aquifer.

Q10: What is aquifer?

Answer: 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.

Q11(NCERT): 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.  By this process of infiltration, groundwater gets recharged.

Q12(NCERT): There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?
OR
Q: Can we keep on drawing water from under the ground? How will it affect the water table?

Answer: Groundwater is an important source of fresh water. Due to unnecessary drawing of water by tube wells and the water table not being replenished/recharged properly may lead to depletion of water table. This would further lead to shortage of freshwater in that area.

Q13: Name the process by which groundwater is recharged.

Answer: Infiltration.

Q14: Why does the earth appear blue when seen from the space?

Answer: Three fourth of the earth surface is covered with water (in the form of seas and oceans). The water absorbs all colours of the sunlight except blue. This blue light is radiated back thus giving blue appearance.

Q15(NCERT): You have been asked to maintain a garden. How will you minimise the use of water?

Answer: Following ways can be adopted to minimise use of water:
  1. By implementing drip irrigation system and sprinklers.
  2. Watering during morning and evening hours will check the loss of water due to evaporation.


Q16(NCERT): Explain the factors responsible for the depletion of water table.

Answer: Factors responsible for the depletion of water table:
  1. Increase in population
  2. Increase in agricultural activities 
  3. Rapid Urbanization
  4. Deforestation
  5. Mismanagement of water resources.
  6. Insufficient rainfall

Q17(NCERT):  Fill in the blanks with the appropriate answers:

Answer:
(a) People obtain groundwater through _wells__ and _tubewells__.
(b) Three forms of water are _solid__, _liquid__ and _gas/vapour__.
(c) The water bearing layer of the earth is _water table__.
(d) The process of water seepage into the ground is called _infiltration_.

Q18(NCERT): 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

Q19(NCERT): 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.


Q20(NCERT). Make a sketch showing groundwater and water table. Label it.

Answer:
groundwater and water table
Water Table
(image credits:openclipart)

Q21: See the water cycle in the figure below. Name the number labels as shown.


Answer:
   ➀ ground water
Agarsen ki Baoli at Delhi
it was constructed in 14th century
credits:wikipedia
   ➁ evaporation
   ➂ condensation
   ➃ clouds
   ➄ transpiration
   ➅ Infiltration
   ➆ precipitation


Q22: What is a baoli?

Answer: Baoli or Bawri is a structure which was used traditionally in India to store rainwater and recharge groundwater. Now-a-days it is voiced to revive this practice as a part of rain water harvesting.


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