Questions & answers for Chapter 14 Water

(a) About two third of the Earth is covered with water while only one-third is dry land. Most of this water is in the form of seas and oceans.

(c) The sea water contains lots of dissolved salts and minerals in it. This makes the sea water salty in taste, so it is also called saline water (salty water). This saline water is unfit for drinking or any other purpose like in agriculture, industry etc.

(b) Evaporation is the process in which water changes into water vapours on heating. As the water is heated it changes into its vapours. This occurs at all times by the heat of the sun as the water on the roads, wet clothes, etc. dry up.

(c) Salt is mixed in water it dissolves in water. This mixture can be separated by the method of evaporation. When the mixture is heated water changes into water vapours and evaporates while salt is left behind in the container.

(d) Evaporation is the process in which water changes into water vapours due to heat. It is a slow process as we do not find too much change in the level of bucket full of water. The heat of the sun heats up the air around us and the hot air is also responsible for causing evaporation where direct heat of the sun is unable to reach. On a hot summer day, the sun shines very brightly and due to much heat evaporation takes place faster. So the clothes dry faster on a hot summer day.

(a) Transpiration is the process by which the plants lose water in the form of water vapours. It is a way by which plants get rid of excess water present in them after carrying out the process of photosynthesis.

(b) When ice is kept in a glass it starts melting due to heat of the surrounding air. There appears on the outside of the glass tiny drops of water. These drops are the water vapours present in air which condense when they come in contact with cooler surface of the glass.

(c) These drops of water are the water vapours present in the surrounding air which condense on coming in contact with the cooler surface of the glass due to ice present in it.

(a) Clouds are the tiny drops of water. These drops of water are formed when the water vapours present in the air move to a higher altitude, where the air is cooler. So these water vapours condense at higher altitudes and form drops of water which collect together and forms clouds.

(a) Ground water is the water present inside the ground. This water reaches there by seeping of the rain water through the soil. It is obtained by hand pumps and tube wells and ground water also acts as a source to many lakes.

(d) When there are too many hand pumps and tube wells in an area, the ground water is used more. This results in loss of ground water and the level of water falls. Then the ground has to be dug much deeper to reach the level of ground water, which falls much lower due to overuse of ground water.

(b) Fog appears when the water vapours present in the air condense. It happens usually in winters where the temperature is very low and due to cold the water vapours condense and fog is seen.

(c) Rain water harvesting is the process by which the rain water is collected and made to seep through the ground to increase the level of ground water which falls low due to overuse of ground water. If the rain water is not harvested it gets washed off in the drains and does not seep through the ground as most of the land is covered with concrete. Thus this ground water can be later used as and when required.

(a) When the rain water is harvested and made to seep through the ground, the level of ground water increases. As a result the hand pumps and tube wells will have more water and they will have to be dug less deep as water level increases.

(c) Roof top rain water harvesting is the method where the rain water falling on the roofs is collected in a storage tank through pipes. It is then filtered as it contains dirt and mud before use. The water can directly be sent to a pit in the ground which will increase the level of ground water.

(d) Excessive rains cause floods which wash away the top soil along with it. Water cycle is responsible for the circulation of water in the atmosphere. In this way no water is lost from the earth, it evaporates and then condenses and falls back on the earth. Draught is the condition of no rain fall in an area for over a long period of time. Ground water is the water present inside the earth which can be obtained through wells, hand pumps and tube wells.