WATER
From where we get water from?
There are many sources of water :
•Ponds
•Lakes
•Rivers
•Wells
About two-thirds of the earth is covered with water.
Water cycle :
Process of the water cycle –
•Disappearing trick of water –
#The process of changing of water into water vapours is called evaporation.
# The water evaporated from the fields, roads, rooftops and other land areas and changes into vapours.
# In sunlight, evaporation takes place faster.
# Evaporation of water is a slow process.
# Remaining part of the water is released by the plants into the air through the process of transpiration.
# So water vapour enters the air through the process of –
•Evaporation
•Transpiration
# Water of seas and oceans is saline as many salts dissolved in it.
•How are clouds formed?
# The process of changing water vapours into water is called condensation.
# When air moves up, it gets cooler and cooler. At a certain height, the air becomes so cool that the water vapours in it, condense to form tiny droplets(tiny drops of water)
# These droplets appear to us like clouds.
# Some drops of water become so heavy that they begin to fall, these falling water drops are called rain.
•Back to the oceans
# Water that falls on the land as rain and snow go back to oceans, lakes and ponds. A part of the rainwater gets absorbed by the ground as groundwater.
# Again,water from ocean,lakes etc evaporates in form of vapours than it gets condense and again fall in form of rain. and this circulation of water is known as the water cycle.
# This is a continuous process.
What if it rains heavily?
Excess rainfall may lead to many problems such as –
•Rise in the level of water.
•Flood
•Affect the animals living in the soil.
What happens if it does not rain for a long period ?
If it does not rain for a long period, the groundwater may become scarce. This may lead to drought.
Rainwater harvesting –
Collecting rainwater and store it for later use.
# Two techniques-
•Rooftop rainwater harvesting – Rainwater is collected from the rooftop to a storage tank through pipes which need filtration before use
•Allow water to go into the ground directly from drains.
Exercise
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 _________.
(a) evaporation.
(b) condensation.
(c) drought
(d) floods.
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.
(a) Condensation
(b) Evaporation
(c) Condensation
(d) Evaporation
(e) Evaporation
3. Which of the following statements are “true”?
(a) Water vapour is present in the air only during the monsoon.
(b) Water evaporates into the 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.
(a) False
(b) False
(c) True
(d) False
(e) True
4. Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?
Answer:
A surface area for evaporation increases on spreading uniform which lead to an increase in the rate of evaporation because as surface area increases, the rate of evaporation also increases.
5. Take out a cooled bottle of water from the refrigerator and keep it on a table. After some time you notice droplets of water around it. Why?
Answer :
On taking out a cooled water bottle from refrigerator, air which surrounds the bottle cools down and get condense in the surface of the bottle.
6. To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.
Answer:
Glasses become wet because air which comes out while breathing contains droplets which on cooling get condense in glasses.
7. How are clouds formed?
Answer:
As we go higher from the surface of the earth, the air gets cooler and become so cool at a certain height. The water vapours present in it condenses to form tiny droplets that appear to us like clouds.
8. When does a drought occur?
Answer:
Drought occurs if it does not rain for a long period. The soil becomes dry and the groundwater may become scarce which may lead to drought.
