please explain:

Question

A charged particle is placed in an electric field that varies with location. No force is

exerted on this charge:

A) at locations where the electric field is zero

B) at locations where the electric field strength is 1/(1.6  10

–19) N/C

C) if the particle is moving along a field line

D) if the particle is moving perpendicular to a field line

E) if the field is caused by an equal amount of positive and negative charge

Answer 1

If the only force in the problem is the electric force, then the electric field must be zero if the force is zero, so the particle must be at a location where the electric field is zero. Answer (A) is correct.