What is the potential difference between a point 0.48 mm from a charge of 2.9 nc and a point at infinity?

The potential at a distance r from a charge Q is given by

where ke is the Coulomb's constant.

The charge in our problem is ; for the point at , the potential is


For the point at infinity, we immediately see that the potential is zero, because  and so .

Therefore, the potential difference between the two points is