Question

A 30.0-mg

oil drop carrying a charge of +4.0 μC

μCpasses undeflected through a region in which there is a uniform, constant electric field.

Determine the electric field.

Express your answer with the appropriate units. Enter a positive value if the field is directed upward and a negative value if the field is directed downward.

Answer 1

The equilibrium of forces makes this happen:

$$F_e=F_g,\\\space\\ qE=mg,\\\space\\ E=\frac{mg}{q}=73.5\text{ V/m}.$$