Question

A charge of +6.0µC experiences a force of 2.0 mN in the +x-direction at a certain point in space. (a) What was the electric field there before the charge was placed there? (b) Describe the force a - 2.0µC charge would experience if it were used in place of the +6.0µC charge.

Answer 1

(a) The electric field is directed toward positive x-axis. The magnitude of field

$$E=\frac{F}{q}=\frac{2.0*10^{-3}}{6.0*10^{-6}}=333\:\rm N/C$$

(b) The force on the negative charge is directed opposite to the field. The magnitude of force

$$F=qE\\ =2.0*10^{-6}*333=6.7*10^{-4}\;\rm N$$