Question

A metal sphere contains zero net charge.

a. Explain why it is incorrect to say that the ball has no charge.

b. Is it possible for the ball to have a positive (or negative) charge on one side yet still have zero net charge? If so, describe how this could be done.

Answer 1

(a) A metal sphere has 0 net charge. This means that the net value of positive and negative charges are equal.

So, if a sphere has + 1C and - 1C charge , its net charge will be zero, but it has both positive and negative charge

So it is incorrect to say that the ball has no charge

(b) Yes, it is possible.

Suppose we take an uncharged metal sphere of inner radius R and thickness t.

We place a point charge Q at the centre.

Now, the property of a conductor is that charge occurs only at the surfaces and the electric field inside a conductor must be 0 [Here, in thickness t]

Let charge accumulated in inner surface be q.

Now, electric field in the thickness t = 0

=> electric field due to Q + electric field due to charge on inner surface = 0

=> kQ/r² + kq/r² = 0

=> Q +q =0

=> q = -Q

Since the sphere has net 0 charge, charge on outer surface q' = 0-q = Q

This is one of the ways to achieve the stated