If hf equals φ, the kinetic energy of emitted electrons is what?

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If hf equals φ, the kinetic energy of emitted electrons is what?

In the photoelectric effect, each photon carries energy hf. To free an electron from a material, at least the work function φ is needed to overcome the binding. Any energy left after overcoming φ becomes the kinetic energy of the emitted electron. If hf equals φ exactly, there is no leftover energy, so the emitted electron has zero kinetic energy. The emission can still occur at this threshold, but the electron would be released without speed. The general relation is KE_max = hf − φ, which gives zero in this case; only if hf were greater than φ would the electrons have positive kinetic energy.

In the photoelectric effect, each photon carries energy hf. To free an electron from a material, at least the work function φ is needed to overcome the binding. Any energy left after overcoming φ becomes the kinetic energy of the emitted electron. If hf equals φ exactly, there is no leftover energy, so the emitted electron has zero kinetic energy. The emission can still occur at this threshold, but the electron would be released without speed. The general relation is KE_max = hf − φ, which gives zero in this case; only if hf were greater than φ would the electrons have positive kinetic energy.

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