An uncharged solid spherical conductor of radius R has an off-center cavity. A point charge +Q is placed inside the cavity. The outer surface of the conductor is then connected to the earth. What is the net charge on the conductor and the magnitude of the electric field at a distance r ( r > R ) from the center of the sphere?

Step-by-step solution

When a point charge +Q is placed inside the cavity, it induces a charge -Q on the inner surface of the cavity and a charge +Q on the outer surface of the conductor. When the outer surface of the conductor is earthed, its potential becomes zero. The induced charge +Q on the outer surface flows to the earth. However, the induced charge -Q on the inner surface remains bound due to the electrostatic attraction of the +Q charge inside the cavity. This is necessary to maintain a zero electric field inside the bulk of the