$A$ clock which keeps correct time at $20^{\circ} C$,is subjected to $40^{\circ} C$. If the coefficient of linear expansion of the pendulum is $12 \times 10^{-6} /{ }^{\circ} C$,how much time will it gain or lose per day?

Two holes of unequal diameters $d_1$ and $d_2$ $(d_1 > d_2)$ are cut in a metal sheet. If the sheet is heated,then:

Three rods of equal lengths are joined to form an equilateral triangle $ABC$. $D$ is the mid-point of $AB$. The coefficient of linear expansion is $\alpha_1$ for the material of rod $AB$ and $\alpha_2$ for the material of rods $AC$ and $BC$. If the distance $DC$ remains constant for small changes in temperature,then:

To keep constant time,watches are fitted with a balance wheel made of:

What is thermal expansion? Write only its types.

$A$ thin copper wire of length $l$ meters is heated by $10^{\circ}C$,resulting in a $2\%$ increase in its length. If a square copper sheet of side $l$ meters is heated by the same $10^{\circ}C$,what is the percentage change in its area?