Tuesday , July 5 2022

NCERT 7th Class (CBSE) Science: Water: A Precious Resource

Question: How cloud is formed?

Answer: The evaporated water above the earth surface is carried away by warm air. As the warm air moves higher from the surface of the Earth, it starts to cool down. It is because the water vapour present starts to condense to form tiny water droplets. These droplets float in the air and form cloud.

Question: What is precipitation?

Answer: When clouds rub together heat is produced that melt the cloud into droplets. These droplets collect to form bigger drops of water. Some of them may become too heavy fall down as rain. This process is known as precipitation.

Question: Write short notes on: In filtration, Aquifer.

Answer: In filtration: The water from rain, rivers, lakes and ponds seeps through the soil and fills the space below the ground. The process of seeping of water through the soil is called infiltration.

Aquifer: Some places groundwater is stored between layers of hard rock. This is called aquifer. Water from aquifers is pumped and taken out through hand pumps and tube wells.

Question: Explain how increasing population is responsible for depletion of water table.

Answer: 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. 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.

Question: Explain how increasing industries are responsible for depletion of water table.

Answer: 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.

Question: Explain how increasing agricultural activities are responsible for depletion of water table.

Answer: 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.

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