A barometer made of very narrow tuve (see fig) is placed at normal temperature and pressure. The coefficient of volume expansion of mercury is `0.00018per C^@` and that of the tube is negligible. The temperature of mercury in the barometer is now raised by `1^@C`, but the temperature of the atmosphere does not raised by `1^@C`, but the temperature of the atmosphere does not change. Then the mercury height in the tube remains unchanged.

Explanation

Pressure `P_1=P_2=1 atm=hrhog`
On changing the temperature, g will not change and atmospheric pressure will not change.
`:.hxxrho=const ant`.
When temperature is increased, the density of Hg decreases and hence, h increases.