Q. A metal rod having linear expansion coefficient $2 \times 10^{- 5}℃^{- 1}$ has a length of 1 m at 20$℃$. The temperature at which it is shortened by 1 mm is
A) $- 20℃$
B) $- 15℃$
C) $- 30℃$
D) $- 25℃$
Explanation
(c) From, $l_{2} = l_{1}\left\lbrack 1 + \alpha\left( t_{2} - t_{1} \right) \right\rbrack$
$t_{2} = t_{1} + \frac{l_{2} - l_{1}}{l_{1}\alpha}$
= 20+$\frac{- 10^{- 3}}{1.0 \times 2 \times 10^{- 5}} = - 30℃$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.