Question

A cavity having a point charge $q$ is made in a neutral conductor as shown in the figure. The net electric field at point $\text{P}$ is
[$K=\frac{1}{4\pi {ϵ}_0}$]

• A. $\frac{Kq}{x^2}$
• B. $\frac{Kq}{r^2}$
• C. $\frac{Kq}{R^2}$
• D. Zero

Answer 1

The correct option is B $\frac{Kq}{r^2}$

Clearly, the charge distribution will be as shown in figure,



Due to electrostatic shielding, the charge inside the cavity will not affect the electric field at point $\text{P}$.

Thus, electric field at point $\text{P}$ will be due to charge on outer surface of the conductor alone.
i.e $E_p=\frac{Kq}{r^2}$

Hence, option (d) is the correct answer.