The photoelectric effect can be used to measure the energy of photons because the energy of the emitted electrons is directly related to the photon energy:
- Photon absorption: When light strikes a material, each electron absorbs the energy of a single photon.
- Electron emission: Part of this energy is used to overcome the material’s work function (the energy needed for the electron to escape).
- Measuring kinetic energy: The remaining energy appears as the kinetic energy of the emitted electrons. By measuring how fast the electrons move (their kinetic energy), we can determine how much energy the photons had.
- Calculation: Since the work function of the material is known, the photon energy can be found by adding the work function to the measured kinetic energy of the electrons.
Key point: The photoelectric effect provides a direct way to measure photon energy because each photon transfers its energy to a single electron, making it very precise.