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CBSE Class 7 Science - Water and water cycle

CBSE Class 7 Science - Water and water cycle

Class 7 Science – Water and water cycle
Around 70% of the Earth is wrapped in water in the form of ice, seas, oceans, rivers, lakes, ground water and moisture in the surrounding. But large amounts of water is not suitable for man consumption. Only fresh water is fit for human consumption. Means 0.006% of the water is only available for use.
Water exists in three forms – Solid, Liquid and gaseous form.
  • As a solid form, it resides as glaciers, snow mountains and ice caps at the poles.
  • As a Liquid form, it exists in oceans, seas, rivers, lakes and ground water.
  • As a gaseous form, water vapors in the air.
Water Cycle
The continuous process of evaporation, condensation, precipitation, infiltration of water in nature keeps the level of water on the earth constant is called the water cycle.  Now understand
Evaporation
Evaporation is the process of conversion of water molecules into vapor.Water vapor accumulates in the sky in the form of clouds.

Condensation
Condensation is the process of conversion of water vapor into water by cooling.
Precipitation
Precipitation occurs when water falls from the sky in the form of rain, snow, hail, or sleet.
Infiltration
Infiltration is the process of seeping of water into the ground.
Aquifer
Sometimes, ground water stores between layers of hard rock. This is known as an aquifer. Water in aquifers can be drawn with tube wells and hand pumps.
Watch interesting videos on water cycle of online classes for Class 7 Science
Water table – water seeps into the ground and moves downward, the level below which the ground  is saturated with water,  is called the water table.
Ground water – Ground water is the water drive below the water table.
Depletion of water table
As long as the water drawn from the ground is restored by infiltration of rain water, the water table remains unaffected. The problem begins when we take more water from the ground than is stored by natural means. as the water table reduces, and it is said to have been depleted.
Reasons for depletion of the water table
  • Demand for water increases with the increasing population
  • Further wells are dug and water is hatched from them
  • Increasing demand of water for industrial activities. Example: Construction industry uses tube-wells
  • Increase in agricultural activities, as lakes and streams are not available everywhere, ground water is used for
  • insufficient rainfall is one of the reason for depletion of the water table.
  • Deforestation

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