Question

Particle A carrying a charge of 9.0 nC is at the origin of a Cartesian coordinate system.

(a) What is the electrostatic potential (relative to zero potential at infinity) at a position r = 4.0 m from the origin?

Express your answer with the appropriate units.

(b) With particle A held in place at the origin, how much work must be done by an outside agent to bring particle B, also carrying a 9.0-nC charge, from infinity to r = 4.0 m?

Express your answer with the appropriate units.

(c) Particle B is returned to infinity, and particle A is moved to r = 4.0 m and held there. How much work must be done by an outside agent to bring particle B from infinity to the origin?

Express your answer with the appropriate units.

Answer 1

(a) The potential is

$$V=\frac{kq}{r}=20\text{ V}.$$

(b) The work is

$$W=QV=1.8·10^{-7}\text{ J}.$$

(c) The work is $1.8·10^{-7}\text{ J}.$