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.

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Solution

Atmospheric pressure = 76 cm of Hg

When water is introduced the water vapour exerts some pressure which counter acts at the atmospheric pressure

The pressure drops to 75.4 cm

Pressure of vapour

= (76-75.4) cm

= 0.6

Relative Humidity

= $\frac{V P}{S V P} = \frac{0.6 c m}{1 c m} = 60$ %

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Atmospheric pressure = 76 cm of Hg When water is introduced the water vapour exerts some pressure which counter acts at the atmospheric pressure The pressure drops to 75.4 cm Pressure of vapour = (76-75.4) cm = 0.6 Relative Humidity = VPSVP=0.6cm1cm=60 %

Atmospheric pressure = 76 cm of Hg

When water is introduced the water vapour exerts some pressure which counter acts at the atmospheric pressure

The pressure drops to 75.4 cm

Pressure of vapour

= (76-75.4) cm

= 0.6

Relative Humidity

= $\frac{V P}{S V P} = \frac{0.6 c m}{1 c m} = 60$ %