Page 2 - 3-Lesson Notes-Water Vapour, Dust and Smoke

Procedure–Take a glass tumbler. Fill it with ice. Put it on a tray and observe after some
time.

Observation – The glass tumbler with ice on the tray can be seen with water droplets on
the outer surface of the glass. This is because when air comes in contact with the cold
surface of the tumbler, water vapour in the air condenses and forms droplets on the
surface of the tumbler.

Inference – air contains water vapour.

Dust and Smoke

❖ In a closed room, if we open a part of a window and observe the incoming beam
of sunlight, we will see a large number of dust particles. Even things kept
unlearned for a longer time, contain dust.
❖ The above observations indicate that air contains dust particles. Air contains
smoke also.
❖ The amount of dust and smoke in air varies from place to place. A city is more
polluted with dust and smoke than the village.
❖ It is advised that one should breathe through the nose rather than the mouth, as
the hair and mucus present in the nose prevent the entry of dust particles.
❖ Factories should build outside of the cities and towns to prevent the emission of
smoke.
❖ Air is said to be polluted when gases, dust particles and smoke are present in the
large amount. The substances that cause air pollution are pollutants. They are
harmful to us.

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