A solid conducting sphere of radius 10 cm is enclosed by a thin metallic shell of radius 20 cm. A charge `q = 20 muC` is given to the inner sphere. Find the heat generated in the process, the inner sphere is connected to the shell by a conducting wire.

Options

A. 12 J
B. 9 J
C. 24 J
D. zero

Answer

b

Explanation

On connecting, the entire amount of charge will shift to the outer sphere. Heat generated is
`U_i - U_f = (q^2)/(8 pi epsilon_0 R_1) - (q^2)/(8 pi epsilon_0 R_2)`
=`((20 xx 10^-6) xx 9 xx 10^9)/(2) [(1)/(0.01) - (1)/(0.20)] = 9 J`.