Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature

Options

A. Length 1 m, radius 1 cm
B. Length 1 m, radius 1 cm
C. Length 2 m, radius 2 cm
D. Length 1 m, radius 2 cm

Answer

D

Explanation

Heat current (H) `=Q/t = (kA triangle T)/(l) implies (Q)/(t) prop A/l prop (r^2)/(l)`
`(r^2)/(l)` is maximum for option (d).