Question 1. Fill up the blanks in the following:
(a) The process of changing of water into its vapour is called _________________.
(b) The process of changing water vapour into water is called _________________.
(c) No rainfall for a year or more may lead to _________________ in that region.
(d) Excessive rains may cause _________________.
Solution 1.
(a) The process of changing of water into its vapour is called evaporation.
(b) The process of changing water vapour into water is called condensation.
(c) No rainfall for a year or more may lead to drought in that region.
(d) Excessive rains may cause floods.
Question 2. State for each of the following whether it is due to evaporation or condensation:
(a) Water drops appear on the outer surface of a glass containing cold water.
(b) Steam rising from wet clothes while they are ironed.
(c) Fog appearing on a cold winter morning.
(d) Blackboard dries up after wiping it.
(e) Steam rising from a hot girdle when water is sprinkled on it.
Solution 2.
(a) Water drops appear on the outer surface of a glass containing cold water. Condensation
(b) Steam rising from wet clothes while they are ironed. Evaporation
(c) Fog appearing on a cold winter morning. Condensation
(d) Blackboard dries up after wiping it. Evaporation
(e) Steam rising from a hot girdle when water is sprinkled on it. Evaporation
Question 3. Which of the following statements are “true” ?
(a) Water vapour is present in air only during the monsoon. ( )
(b) Water evaporates into air from oceans, rivers and lakes but not from the soil. ( )
(c) The process of water changing into its vapour, is called evaporation.( )
(d) The evaporation of water takes place only in sunlight.( )
(e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. ( )
Solution 3.
a) Water vapour is present in air only during the monsoon. False
b) Water evaporates into air from oceans, rivers and lakes but not from the soil. False
c) The process of water changing into its vapour, is called evaporation. True
d) The evaporation of water takes place only in sunlight. False
e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. True
Question 4. Suppose you want to dry your school uniform quickly. Would spread it near an anghiti or heater help? If yes, how?
Solution 4. If you want to dry your school uniform quickly then spreading it near an angithi or a heater would definitely help it to dry because an angithi or heater increases the rate of evaporation.
Question 5. Take out a cooled bottle of water from refrigerator and keep it on a table. After some time, you notice droplets of water around it. Why?
Solution 5. We notice droplets of water around a cooled water bottle because the air around the bottle cools down and condenses around the bottle.
Question 6. To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.
Solution 6. People breathe out on glasses because the air that we breathe out has water vapours which condense on the glass of spectacles making it wet. So, it becomes easier to clean the spectacle with this little amount of water.
Question 7. How are clouds formed?
Solution 7. When the water vapours which are present in the air move upward it gets cool because the as we move up from the earth’s surface the temperature gets cooler and cooler. At a sufficient height, the water vapour in the air becomes so cold that it condenses and becomes water droplets. These water droplets due to their very small size appear to us like a cloud.
Question 8. When does a drought occur?
Solution 8. When it does not rain for more than two years, the underground water level decreases and a huge amount of water gets lost because of the process of transpiration and evaporation. The soil gets because water does not get back to earth’s surface by rain. All the water bodies may even dry up because of insufficient or no rain. These conditions lead to drought.