Q$4.$ A frame $abc$ is fixed at point a and free at point $c.$ The frame gets heated under the sun so that the outer surfaces reach a temperature of $T+T$ while the inner surfaces remain at temperature $T.$ All members have the same rectangular cross section with height $($between outer and inner surface$)h$ and are made of the same material with coefficient of thermal expansion $.$

$(ans$: $T\frac{l_1+l_2}{h})$