The end of two rods of different materials with their thermal conductivities, area of cross-section and lengths all in the ratio 1:2 are maintained at the same temperature difference. If the rate of flow of heat in the first rod is `4 cal//s`. Then, in the second rod rate of heat flow in `cal//s ` will be

Options

A. 1
B. 2
C. 8
D. 16

Answer

C

Explanation

`R = l/(KA)`
`R_2/R_1 = (l_2/l_1)(K_1/K_2 * A_1/A_2)`
`=(2)(1/2)(1/2) = 1/2`
Therefore, thermal resistance of `2^nd` rod is half.
Hence, rate of heat will be twice.