Page 148 - Science Class 06
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v The exposed surface of the wet object WHERE DOES RAIN COME FROM?
also influence the rate of evapora on. The sun heats up the water of river, lakes,
The large the exposed area, faster the seas and oceans and the water starts turning
rate of evapora on. into water vapour due to evapora on. The
CONDENSATION water vapour mixes up with air. A given
mass of air can hold only a certain amount
Condensa on is the change of water from
of water vapour. This amount depends upon
its gaseous form (water vapour) into liquid
the temperature. The higher the tempera-
water. Condensa on generally occurs in the
ture, the more vapour air can hold.
atmosphere when warm air rises, cools and
The water vapour being light, rises up in the
looses its capacity to hold water vapour. As
air. As the temperature at very high al tude
a result, excess water vapour condenses to
is low, the water vapour condenses at a
form cloud droplets. The upward mo ons
certain height. About one kilometre or more
that generate clouds can be produced by
above the sea level it forms cloud. When
convec on in unstable air, convergence
the temperature is considerably below
associated with cyclones, li ing of air by
freezing, the water vapour may condense
fronts and li ing over elevated topography
into liquid and come to the earth in the
such as mountains. form of water droplets called rain. This
process is called precipita on.
Aim : To show the process of How are Clouds Formed?
condensa on. Cloud is a mass of small water drops or ice
Materials Required : A glass and ice cyrstals formed due to condensa on of
cubes. water vapour at very high al tude in free air.
Method : Keep a few ice cubes in a glass Warm air is less dense than cold air and
and keep it on a table. A er a few hence rises upward. Its place is then taken
minutes, you will observe ny water by cooler air which in turn warms up. The
droplets on the outer surface of the rising air moves away from the warm place.
glass. Where do the droplets come It gradually gets cooler un l it reaches the
from? Actually, air contains water vapour satura on point. The maximum amount of
in a small amount. When the water water vapour that air can hold is called
vapour of air comes in contact with the satura on point. At high al tude when
cold surface of the glass, it is condensed temperature goes below this point, the
and turns into ny water droplets. water vapour begins to condense and
clouds are formed.
WATER CYCLE
The con nuous circula on of water on the
earth is known as water cycle. Water is the
148 Science-6
