What does the work function represent in the photoelectric effect?

• A. The energy needed to liberate an electron from the surface
• B. The kinetic energy of the emitted electron
• C. The energy of the incident photon
• D. The energy stored in the nucleus

Answer: (A)

The work function is the energy required to remove an electron from a material’s surface and place it into vacuum. Imagine the surface as a barrier; you must supply at least that amount of energy to let the electron escape. In the photoelectric effect, the incoming photon provides energy h f; at least φ, the work function, must be used to overcome the surface binding, and any leftover energy becomes the electron’s kinetic energy. So the maximum kinetic energy of the emitted electron is h f minus φ, and if h f is less than φ, no emission occurs. This concept is about binding to the surface, not about the photon’s energy itself or any nuclear energy. The work function depends on the material and surface condition.