Question: Fill up the blanks in the following:
- The process of changing of water into its vapour is called ________ .
- The process of changing water vapour into water is called ________ .
- No rainfall for a year or more may lead to ________ in that region.
- Excessive rains may cause ________ .
- evaporation or vaporization
Question: State for each of the following whether it is due to evaporation or condensation:
- Water drops appear on the outer surface of a glass containing cold water.
- Steam rising from wet clothes while they are ironed.
- Fog appearing on a cold winter morning.
- Blackboard dries up after wiping it.
- Steam rising from a hot girdle when water is sprinkled on it.
Question: Which of the following statements are “true”?
- Water vapour is present in air only during the monsoon.
- Water evaporates into air from oceans, rivers and lakes but not from the soil.
- The process of water changing into its vapour is called evaporation.
- The evaporation of water takes place only in sunlight.
- Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler.
Question: Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help you? If yes, how?
Answer: Yes, to dry the school uniform quickly, the uniform is spread near an anghiti or heater because evaporation is rapid at higher temperature. Higher the temperature faster is the rate of evaporation. So the uniform is dried up quickly.
Question: Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a puddle of water around it. Why?
Answer: The cooled water bottle has very cold exposed surface. Due to cool surface there is condensation of water-vapour from air on the surface of water bottle because water vapour is present in atmosphere. The condensed water molecules spread around the bottle. So a puddle of water is noticed after sometime.
Question: To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet?
Answer: The breathe out gases contain water-vapour. The water-vapour condenses at spectacles so glass becomes wet and with the help of small amount of water, it is easy to clean the spectacles.
Question: How are clouds formed?
Answer: The water present on the earth evaporates due to heating by the sun. The water vapour in the air condenses to form tiny droplets of water at high altitude, which appears as clouds. Thus clouds are formed by the condensation of water vapors present in air at high altitude.
Question: When does a drought occur?
Answer: If there is no rain for a long period or for many years then there is scarcity of water in that region. This leads to drought.
Question: Write the sources of water on the earth.
Answer: Sources of water on the earth are: Seas, Oceans, Rivers, Springs, Tube-wells etc.
Question: In which forms, water exists on the earth?
Answer: Water exists on the earth in all three physical forms: ice, water and water vapour.
Question: What is transpiration?
Answer: Loss of water in the form of water vapour through stomata of leaves is called transpiration.
Question: How are the clouds formed?
Answer: Clouds are formed by the condensation of water vapour at high altitude.
Question: What is meant by the conservation of water?
Answer: Careful, economical and wise use of water and avoiding the wastage of water is called conservation of water.
Question: Mention two main functions of water for living organisms.
Answer: Two main functions of water for living organisms are:
- Water is essential for the germination of seeds, growth of plants and in photosynthesis.
- Water is used for the transportation of people and goods.
Question: Why is ocean water not suitable for domestic use?
Answer: Sea and ocean water contains large amounts of various salts. It is due to these salts the ocean water is salty and cannot be used for drinking, washing and for irrigation purposes.
Question: Why does the water split on the floor disappear after some time?
Answer: Due to evaporation the water split is changed into water vapour. So it disappears after some time.
Question: How does heavy rain affect us?
Answer: Heavy rains may cause:
- A rise of water level in dams, rivers, lakes etc.
- Water-logging and floods.
- Floods cause damage to property, crops and animals.
Question: How does the failure of rainfall affect people on the earth?
Answer: The failure of rainfall can cause the following:
- The soil becomes dry.
- Water level in rivers, lakes, dams, etc. may fall. Ponds and canals may even dry up.
- The ground water level falls.
Question: Name two processes responsible for the formation of clouds.
Answer: Evaporation and transpiration.
There are 4 containers A, B, C and D with same amount of water in each. Answer the following based on them.
- Name the container in which water will evaporate faster than all others.
- Name the container in which water will evaporate very slowly.
Give reason for your answer.
- C – More is the exposed surface area, more will be evaporation of water.
- B – As it is closed, no evaporation takes place.
Question: During winters why do we see more fog in close areas where there are lots of trees?
Answer: Due to lots of trees, air at that place contains much more water vapour during winters. These vapour condense on dust or smoke particles forming thick fog.
Question: What is meant by conservation of water? Suggest three methods to conserve water.
Answer: Careful and economical use of water and avoiding its wastage is called conservation of water.
Suggestions for conserving water:
- Use only the required quantity of water.
- Trees and forests help in causing rainfall. So to conserve water, we should plant more and more trees.
- By collecting rainwater in tanks, ponds or by constructing check dams.
Question: What is rainwater harvesting? Describe the method of rainwater harvesting.
Answer: Rainwater harvesting is the collection of rainwater and storing for future use. In this system rainwater in collected from the rooftops by means of pipes into storage tank for later use.
Methods of Rainwater Harvesting:
- Rooftop rainwater harvesting. In this system, the rainwater from the rooftop is collected in a storage tank, through pipes.
- Another method, a big pit is dug near house for collecting rainwater. This pit is filled with different layers of bricks, coarse gravels and sand or granite pieces.