How does the energy of the incident photon relate to the kinetic energy of the emitted electron?

In the photoelectric effect, the energy of an incident photon is partly used to release the electron from the material and any leftover energy becomes the kinetic energy of the emitted electron:

1. Photon energy absorption: Each electron absorbs the energy of a single photon.
2. Overcoming the work function: Part of the photon’s energy is spent to overcome the material’s work function—the energy needed for the electron to escape.
3. Remaining energy becomes motion: Any energy left after overcoming the work function is converted into the electron’s kinetic energy, so the electron moves faster if the photon is more energetic.

Key point:

• Higher photon energy → higher kinetic energy of electrons, as long as the photon’s energy exceeds the work function.
• If photon energy equals the work function, electrons are emitted with almost no kinetic energy.
• Photon energy below the work function cannot release electrons at all.