Question

A solid conducting sphere of radius $10cm$ is enclosed by a thin metallic shell of radius $20cm$. A charge $q=20\mu C$ is given to the inner sphere. Find the heat generated in the process when the inner sphere is connected to the shell by a conducting wire :

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

Answer 1

The correct option is B $9J$

On connecting, the entire amount of charge will shift to the outer sphere. Heat generated is
$U_i-U_f=\frac{q^2}{8\pi {\epsilon }_0{R}_1}-\frac{q^2}{8\pi {\epsilon }_0{R}_2}$
$=\frac{(20\times {10}^{-6})\times 9\times {10}^9}{2}[\frac{1}{0.10}-10.20]=9J$