On what does the value of the coefficient of linear expansion depend?

If two rods of lengths $L$ and $2L$,having coefficients of linear expansion $\alpha$ and $2\alpha$ respectively are connected end-to-end,then find the average coefficient of linear expansion of the composite rod.

To increase the length of a metal rod by $0.4 \%$, the temperature of the rod is to be increased by (Coefficient of linear expansion of the metal $= 20 \times 10^{-6} \ {}^{\circ}C^{-1}$) (in $K$)

$A$ solid expands upon heating because

Two metal strips that constitute a thermostat must necessarily differ in their

$A$ seconds pendulum clock has a steel wire. The clock shows correct time at $25^{\circ} C$. How many seconds does the clock lose or gain in one week,when the temperature is increased to $35^{\circ} C$? (Given: $\alpha_{\text{steel}} = 1.2 \times 10^{-5} /^{\circ} C$)