A solid spherical conductor of radius 1.50 m has a small spherical cavity of radius 0.50 m with the same center. The net charge of the conductor is zero. An object with a net charge of 4.00 nC is placed inside the cavity in such a way that it is isolated from the conductor. a) What is the charge on the inner cavity surface? b) what is the electric field magnitude 3.00 m from the center of the sphere?