Question

In the photoelectric effect, what happens to the stopping voltage when the light frequency is decreased?

Answer 1

The energy of the emitted electrons is proportional to the energy of the incoming photon which is proportional to frequency.
Therefore if you decrease the frequency you decrease the energy of each electron and it takes less voltage to stop it.
See below excerpted from wikipedia:
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"Experimental results of the photoelectric emission

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" For a given metal of particular work function, increase in frequency of incident beam increases the maximum kinetic energy with which the photoelectrons are emitted, but the photoelectric current remains the same, though stoppage voltage increases.
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