Q. A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with the two reservoirs in time t?
A) Q/2
B) Q/4
C) Q/16
D) 2Q
Explanation
[Solution from source] Volume is fixed: halving the radius makes the area A/4, so the length becomes 4L. Heat flow ∝ A/L, so it becomes ¼ ÷ 4 = 1/16 of the original: Q/16. Taking only the area change gives Q/4. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.