Water
Chapter 14
অনুশীলনী (Exercises)
- Fill up the blanks in the following:
(a) The process of changing of water into its vapour is called _ .
Ans:- Evaporation.
(b) The process of changing water vapour into water is called _ .
Ans:- Condensation.
(c) No rainfall for a year or more may lead to __ in that region.
Ans:- Drought.
(d) Excessive rains may cause _ .
Ans:- Floods.
- State for each the following whether it is due to evaporation (বাষ্পীভৱন) or condensation (ঘনীভৱন):
(a) Water drops appear on the outer surface of a glass containing cold water.
Ans:- Evaporation.
(b) Steam rising from wet clothes while they are ironed.
Ans:- Condensation.
(c) Fog appearing on a cold winter morning.
Ans:-Evaporation.
(d) Blackboard dries up after wiping it.
Ans:-Evaporation.
(e) Steam rising from a hot girdle when water is sprinkled on it.
Ans:- Evaporation.
- Which of the following statements are “true”
(a) Water vapour is present in air only during the monsoon.
Ans:- False.
(b) Water evaporates into air from oceans, rivers and lakes but not from the soil.
Ans:- False.
(c) The process of water changing into its vapour, is called evaporation.
Ans:- True.
(d) The evaporation of water takes place only in sunlight.
Ans:- False.
(e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler.
Ans:- True.
- Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?
Ans:- We know that heat evaporates or converts water into steam. A lot of heat is produced in the ring stove or heater. Therefore, if the uniform is mixed with the ring stove or heater, the water in the cloth evaporates and mixes into the air and it will dry quickly.
- Take out a cooler bottle of water from refrigerat or and keep it on a table. After some time you notice a puddle of water around it. Why?
Ans:- The said process is the form of condensation process occurring in the air. The raw surface of a cold water bottle extracted from the refrigerator squeezes the air around it and the water vapor in the air condenses on the surface of the bottle.
- To clean their spectacles (চশমা), people often breathe out on glasses to make them wet. Explain why the glasses become wet.
Ans:- We cannot survive without air. We use air (oxygen gas) to breathe. Once this air is used in our body’s respiratory function, we exhale the volatile air (carbon dioxide gas). Some amount of water vapor is also released along with the air we exhale. Due to the presence of that water vapor, it becomes moist when it exhales in the two glasses.
- How are clouds (ডাৱৰ) formed?
Ans:- It keeps cooling down gradually as the air is going up. The air becomes so cold at a sufficient height that the water vapor in it condenses to form tiny droplets of water. These tiny droplets float in the air. We call it dawar.
- When does a drought (খৰাং) occur?
Ans:- If an area does not rain for a year or more, the soil and climate in that area become dry. Without rain in the region the soil continues to lose water by evaporation and prabhased. The water levels in the streams or ponds in that area go down, even as some of them dry up. There is a shortage of ground water. This leads to drought.