For the photoelectric effect, emission occurs only if the photon energy hf is at least the work function φ. Which statement expresses this condition?

For the photoelectric effect, emission occurs only if the photon energy hf is at least the work function φ. Which statement expresses this condition?

• A. hf ≥ φ
• B. hf < φ
• C. hf = 0
• D. hf ≤ φ

Answer: (A)

In the photoelectric effect, the energy from each photon must be enough to overcome the binding energy of the electron to the surface, which is the work function φ. The photon energy is hf, so the condition for emission is hf ≥ φ. If hf is less than φ, the photon cannot provide enough energy to liberate the electron, so no emission occurs. If hf equals φ, the photon just supplies the required energy and the emitted electron has essentially zero kinetic energy. If hf is greater than φ, the extra energy hf − φ becomes the kinetic energy of the emitted electron.

In the photoelectric effect, the energy from each photon must be enough to overcome the binding energy of the electron to the surface, which is the work function φ. The photon energy is hf, so the condition for emission is hf ≥ φ.

If hf is less than φ, the photon cannot provide enough energy to liberate the electron, so no emission occurs. If hf equals φ, the photon just supplies the required energy and the emitted electron has essentially zero kinetic energy. If hf is greater than φ, the extra energy hf − φ becomes the kinetic energy of the emitted electron.