Coefficient of linear expansion of brass and steel rods are  α1and α2 Lengths of brass and steel rods are l1and l2respectively. If (l2-l1) is maintained same at all temperatures, which one of the following relations holds good?

Linear expansion of brass =α1 Linear expansion of steel =α2 Length of brass rod =l1 Length of steel rod =l2On increasing the temperature of the rods by ∆T, new lengths would bel1'=l11+α1ΔT........(1)l2'=l21+α2ΔT.........(2) Subtracting eqn. (i) from eqn. (ii), we get l2'-l1'=l2-l1+l2α2-l1α1ΔTAccording to the question l2'-l1'=l2-l1∴l2α2-l1α1=0 or l1α1=l2α2