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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»

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= \(\frac {(m*g)}{e}\).



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