Answer Posted / km jyoti saini
Atmosphere:-The earth is surrounded on all sides by a gaseous enveloped known as atmosphere. This extends upto a height of many miles above the surface of earth. It is composed of a mixture of oxygen, nitrogen with small quantities of carbon dioxide, water vapours and rare gases. It is divided onto a number of layers. The air near sea-level is the densest because near the surface it is compressed to the maximum extent by the weight of a very long column of air. The air becomes thinner and thinner as we go up.
Atmospheric pressure:-The force per unit area due to a column of air is caked pressure of the atmosphere. Its value is 14.7 lb/sp. In or 1013000 dynes/sp.cm
Like liquids, the atmosphere also exerts pressure in all directions i.e upward, downward and sideways.
Experimentally it can be shown as:-
I. Fill a glass tumber with water and lay a sheet of cardboard over the top pressing it down. It will be found that glass may be inverted without the water falling out. The card had been held by the thrust of the atmosphere upwards on the upper side which shows that atmospheric pressure is greater than the pressure of water column
II. Rise of a liquid in a evacuated tube is due to atmospheric pressure but there is a limit upto which a liquid can rise into it
III. Take a funnel and tie a thin rubber sheet and its wide end and suck out the air through the barrow end the rubber is pushed inwards due to air pressure outside
Barometer:-Such instruments by which pressure of the atmosphere can be measured are called barometer. Some of them are Syphon barometer, Forth’s barometer, Aneroid barometer Barograph or self – registering barometer
The barometer is used.
(i)For finding atmospheric pressure
(ii)Determination of height and
(iii)For forecasting weather
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