An electron is passing through a field but no force is acting on it. Under what conditions is it possible, if the motion of the electron be in the (i) electric field (ii) magnetic field?

Explanation

(i) In electric field, there is always a force on the moving electron opposite to the direction of field. Thus the force will be zero only if electric field is zero.
(ii) In magnetic field, the force acting on a moving electron is
`F=qvBsin theta`, it is zero if `theta=0^@` or `180^@`.
i.e., the eletron is moving parallel to the direction of magnetic field.