Science [3 Marks Each] QUE-ANS

A drought occurs if there is no rainfall for a long time. Usually, water lost by soil due to evaporation is returned to it by rains. But no rainfall occurs for a long time, it leads to a decrease in the water level of various ponds and wells. This leads to the condition of drought.

Main processes that help in circulation of water in nature are evaporation and condensation.
The process of conversion of water into its vapour is known as evaporation. Evaporation of water takes place continuously from oceans, rivers and other water bodies such as lakes and ponds. This water vapour becomes a part of the atmospheric, air.
The water vapour present in the air moves to different places along with the wind. When vapour reaches at a certain height, it gets cooled and turns into very tiny water droplets. These droplets become visible to us in the form of clouds. Ultimately, the water comes down to the surface in the form of rain or snow. This process of conversion of vapour into water is known as condensation.
Circulation of water by evaporation and condensation in this manner is known as water cycle.

1. Water is a precious gift of nature.
2. We should not waste it. Try to ‘save every drop of water’.
3. Always be careful that water tank in your house does not overflow when it is being filled.
4. If we leave the tap running while brushing our teeth, nearly 16 litres of water get wasted. We should fill a mug of water and use that instead.
5. We should not water our garden by drinking water instead we have to reuse the water from washing clothes and cleaning utensils.

Water kept under the shade of a tree also evaporates because of warm air. Actually, during day time, the heat given out by the sun heats all the air around us. This warm air provides heat for evaporation of water kept in the shade.

The contamination of water due to human activities is known as water pollution. Causes of water pollution are:

• Washing of clothes and utensils.
• Disposal of household sewage and garbage.
• Disposal of industrial effluent.
• Bathing of animals.

Areas covered with concrete affect the availability of groundwater because concrete reduces the seepage of rainwater into the ground which leads to reduction in the availability of groundwater.

Clouds are formed by the process of evaporation and condensation. Water from the oceans, rivers, lakes, ponds, plants, fields, and other land surfaces evaporates, gets into air, and rises up in the atmosphere. At a certain height when the air becomes cooler, water vapour contained in air condenses. On condensation, these form water droplets. These water droplets collect and float in air as clouds.

There is a need for conserving water because of the following reasons:

1. Increasing population is creating more demand for usable water.
2. Availability of freshwater is decreasing day-by-day.

Wet clothes placed on a clothes line dry after sometime because water present in wet clothes is converted into water vapour and released in atmosphere due to evaporation which leaves them dry.

Sea water reaches a lake or pond is represented by a diagram:

Advantages of water harvesting:

• In areas where there is very low rainfall, water harvesting is the only way to reduce’the water shortage.
• There is an increase in the level of groundwater.
• The effects of drought are lessened.
• Places not situated near a river or large lakes have to rely on groundwater. Water harvesting is very important in such areas.
• Water logging of low-lying roads and streets is prevented.
• Soil and water pollution is reduced.

1. Use a bucket for taking bath.
2. Collect rainwater.
3. Get all leaking pipes repaired.
4. Instead of washing the floor, use a mop.

The process by which land water returns back to a sea or an ocean is as follows:

1. Snow/ Rain falling on the mountains melts into water that flows down in the form of streams and rivers.
2. A part of the rainwater gets absorbed into the ground and rest flow in the form of stream or rivers.
3. The river water after passing through various regions ultimately reaches into a sea or an ocean.

The common salt dissolved in half a cup of water can be recovered by removing the water from the salt solution.
This can be done by heating the solution on a gas stove or keeping it under the sun in a plate for few hours.
Due to evaporation of water in both the processes, we will get the salt back.