A glass tube is attached to the bottom of a thin iron rod of length `1m`. To what height must the glass tube be filled with mercury so that the centre of mass of the pendulum formed will not rise or all with changes in temperature?
(Linear expansivity of glass `=9xx10^(-6)K^(-1)`, that of iron `=12x10^(-6)K^(-1)` and cubical edxpansivity of mercury `=18.2xx10^(-5)K^(-1)`)
