In photoelectric effect the work function of a metal is 3.5 eV. The emitted electrons can be stopped by applying a potential of -1.2 V. Then

the energy of the incident photon is 4.7 eV
the energy of the incident photon is 2.3 eV
if higher frequency photon be used, the photoelectric current will rise
when the energy of photon is 3.5 eV, the photoelectric current will be maximum

Correct answer: the energy of the incident photon is 4.7 eV

Solution

The stopping potential is related to the kinetic energy of the emitted electrons. Using the photoelectric equation, energy of the photon = work function + stopping potential energy. Substituting values: 3.5 eV + 1.2 eV = 4.7 eV.

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