A and B are two concentric spheres If A is given a charge Q while B is earthed as shown in figure :
Answer & explanation
Correct answer: option 3
∵ B is grounded, VB = 0
$\frac{k Q_B}{R}+\frac{k Q_B}{R}=0$ (R = radius of shell B)
$Q_B=-Q_A$
$\sigma_B=-Q$
$\sigma_B=-\frac{Q}{4 \pi R^2}$
But $\sigma_A=\frac{Q}{4 \pi r^2}$
∴ (A) is not correct
Apply Gauss's theorem. Only (C) is correct.