A solid block of copper, which is a good conductor, has a cavity in its interior. Within the cavity, insulated from the conductor, is a point charge of 3.00 nCnC. The block of copper itself has an excess charge of -8.00 nCnC. How much charge is on the outer surface of the block and the surface of the cavity

The charge on the outer surface of the block = -5.00 nC

The charge on the surface of the cavity (on the inner surface of the block) = -3.00 nC

Explanation:

The point charge within the cavity will induce a charge equal in magnitude and opposite in sign on the inside cavities of the copper block.

Charge of the point charge = 3.00 nC

Charge induced on the inner surface of the Copper block's cavity = -3.00 nC

Since the charge on a conductor should usually be neutral, the charge on the inner surface causes a charge equal in magnitude and also opposite in sign on the outer surface of the block; that is, 3.00 nC.

But this block already has an excess charge of -8.00 nC (which resides on the surface because excess charge for conductors reside on the surface of the conductors)

So, net charge on the outer surface of the Copper block = -8.00 + 3.00 = -5.00 nC.

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