Question

An electron of mass m is kept in a vertical electric field of magnitude E. What must be the value of E so that the electron doesn’t fall due to gravity?

(a) m*g*e

(b) \(\frac {e}{(m*g)}\)

(c) \(\frac {(m*g)}{e}\)

(d) \(\frac {1}{(m*g*e)}\)

This question was addressed to me in quiz.

The above asked question is from Electric Field in chapter Charges and Fields of Physics – Class 12

Answer 1

The correct option is (c) \(\frac {(m*g)}{e}\)

Easiest explanation: Gravitational force on the electron is m*g (weight of the electron). Electrical force on the body is e*E. If the electron doesn’t fall then these two forces balance each other, so m*g=E*e. Therefore E= \(\frac {(m*g)}{e}\).