In the photoelectric effect, if hf equals the work function φ, what is the maximum kinetic energy of emitted electrons?

In the photoelectric effect, if hf equals the work function φ, what is the maximum kinetic energy of emitted electrons?

• A. KEmax = hf
• B. KEmax = φ
• C. KEmax = 0
• D. KEmax is infinite

Answer: (C)

In the photoelectric effect, the incoming photon must supply enough energy to overcome the work function φ, and any extra energy goes into the electron’s kinetic energy. The energy balance is KEmax = hf − φ. If hf equals φ, there’s no leftover energy for motion, so the maximum kinetic energy is zero. This is the threshold condition for emission: at or above that energy, electrons are emitted, with KE increasing as hf increases above φ.

In the photoelectric effect, the incoming photon must supply enough energy to overcome the work function φ, and any extra energy goes into the electron’s kinetic energy. The energy balance is KEmax = hf − φ. If hf equals φ, there’s no leftover energy for motion, so the maximum kinetic energy is zero. This is the threshold condition for emission: at or above that energy, electrons are emitted, with KE increasing as hf increases above φ.