A conductor A with a cavity as shown in Fig. is given a charge Q. Show that the entire charge must appear on the outer surface of the conductor.

Explanation

As we know the property of conductor that the net electric field inside a charged conductor is zero. i.e, `E=0`.
Now let us choose a Gaussian surface lying completely inside the conductor enclosing the cavity.
So, form Gauss's theorem `oint E. dS =q/epsi_(0)`
As `E=0 implies q/epsi_(0) =0 implies q=0`
That means the charge inside the cavity is zero. Thus, the charge Q on the conductor must appear on the outer surface of the conductor.