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Question
How will you demonstrate that water vapour is present in air ?
Solution
The presence of water vapour in air can be shown by the following experiment:
Take a steel tumbler and put some well-crushed ice into it and wipe its surface with a clean dry cloth, so as to make its surface completely dry. Allow it to stand for 5 minutes. A large number of drops of water vapour appear on the outer surface of the tumbler. This happens because the air around the steel tumbler contains water vapour in it. When this water vapour comes into contact with the cold outside surface of the steel tumbler, it condenses to form tiny drops of liquid water. The formation of tiny drops of water outside the steel tumbler containing crushed ice, shows the presence of water vapour in air.
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