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Question
A barometer tube is 80 cm long (above the mercury reservoir). It reads 76 cm on a particular day. A small amount of water is introduced in the tube and the reading drops to 75.4 cm. Find the relative humidity in the space above the mercury column if the saturation vapour pressure at the room temperature is 1.0 cm.
Solution
Here ,
Atmospheric pressure , P = 0.76 m Hg
pressure due to water vapour inside , `"P"^' = 0.754 " mHg"`
Vapour pressure = `"P - P"^' = 0.76 - 0.754 = 0.006 " mHg"`
SVH = 0.01 mHg
`"RH" = "Vapour pressure" / "SVH" xx 100%`
= `0.006/0.01 xx 100% = 60%`
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