Q. The ratio of thermal conductivity of two rods of different material is 5:4. The two rods of same area of cross-section and same thermal resistance will have the lengths in the ratio
A) 4 : 5
B) 9 : 1
C) 1 : 9
D) 5 : 4
Explanation
(d) Given $A_{1} = A_{2}$ and $\frac{K_{1}}{K_{2}} = \frac{5}{4}$
$\because R_{1} = R_{2} \Rightarrow \frac{l_{1}}{K_{1}A} = \frac{l_{2}}{K_{2}A} \Rightarrow \frac{l_{1}}{l_{2}} = \frac{K_{1}}{K_{2}} = \frac{5}{4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.