Linear thermal expansion

2016 1 question

1. 1 Thermal Properties of Matter
   Coefficient of linear expansion of brass and steel rods are $\alpha_1$ and $\alpha_2$. Lengths of brass and steel rods are $l_1$ and $l_2$ respectively. If $(l_2 - l_1)$ is maintained same at all temperatures, which one of the following relations holds good?
   A $\alpha_1l_2^2 = \alpha_2l_1^2$ B $\alpha_1^2l_2 = \alpha_2^2l_1$ C $\alpha_1l_1 = \alpha_2l_2$ D $\alpha_1l_2 = \alpha_2l_1$
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