Cavity Inside a Conductor

Consider a conductor with a cavity inside it. A charge q is placed within the cavity. Then the field in the cavity will not be zero.


Consider a Gaussian surface, all points of which are in the conductor. E = 0 on this Gaussian surface, as it is inside the conductor.
Hence by Gauss’s law, the net enclosed charge must be zero.
But            Qenc =  q + qinduced
            qinduced = -q.

A charge q suspended inside a cavity in a conductor induced an equal and opposite charge – q on the surface of the cavity.
The same line of approach can be used to show that the field inside the cavity of a conductor is zero when no charge is suspended in it.


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