Q. A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio 1:4. If the free face of brass is at $100℃$ and that of copper at $0℃$, the temperature of interface is
A) $80℃$
B) $20℃$
C) $60℃$
D) $40℃$
Explanation
(a) Temperature of interface $\theta = \frac{K_{1}\theta_{1} + K_{2}\theta_{2}}{K_{1} + K_{2}}$
[$\because\frac{K_{1}}{K_{2}} = \frac{1}{4} \Rightarrow If\ K_{1} = K\ $then$\ K_{2} = 4K$]
$\Rightarrow \theta = \frac{K \times 0 + 4K \times 100}{5K} = 80℃$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.