Q. A metal rod of length $2m$ has cross sectional areas $2A$ and $A$ as shown in figure. The ends are maintained at temperatures $100℃$ and $70℃$. The temperature at middle point $C$ is
A) $80℃$
B) $85℃$
C) $90℃$
D) $95℃$
Explanation
(c) Let $\theta$ be temperature of middle point $C$ and in series rate of heat flow is same
$\Rightarrow K(2A)(100 - \theta) = KA(\theta - 70)$
$\Rightarrow 200 - 2\theta = \theta - 70 \Rightarrow 3\theta = 270 \Rightarrow \theta = 90℃$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.