Two identical spherical bulbs contain air and are connected by a short horizontal glass tube. The tube contains a short mercury thread in it.Temperature of the two bulbs are `0^@C` and `20^@C` respectively. IF the temperature of each bulb is increased by `10^@C`. what will be the change in the position of the mercury thread?

Explanation

The mercury thread shifts towards the bulb at higher temperature.As the mercury thread is in equilibrium before increasing the temperature the initial pressure on both sides of the thread should be the same.say p, On heating the equilibrium is disturbed and the pressures changes to `p_1` and `p_2` respectively for the bulbs at `(0+10)^@C` or `10^@C` and `(20+10)^@C` or `30^@C` respectively.
Applying Charle.s law for the first bulb
`p_1/p=T_1/T=(273+10)/273=283/273=1.037`
and the second bulb
`p_2/p=T_2/T=(273+30)/(273+20)=303/273=1.034`
`thereforep_1/p_2=(283times293)/(273times303)=1.0024`
As `p_1` is greater than `p_2`, the thread shifts towards the bulb at higher temperature.