Answer to Question #251944 in Electricity and Magnetism for zuzu

Question

a) Find the distance at which you need to place a charge -16 x10^-6C from a charge 10 x10^-9C such that the potential energy between them is equal to 9x10^-5J.

b) Find the potential energy of a system of a charge of +7 x10^-6C is found at 0.06m of another charge of 20 x10^-6C?

Answer 1

a) Determine the potential of the second charge (10 nC):

$$V=kq_2/r.$$

The energy is

$$U=Vq_1=kq_1q_2/r,\\\space\\ r=kq_1q_2/U=16\text{ m}.$$

b) The potential energy is

$$U=\frac{kq_1q_2}{r}=21\text{ J}.$$