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Einstein's photoelectric equation
Intermediate
Kinetic energy equals photon energy minus work function.
K_max = hf − φEach photon gives all its energy hf to one electron: K_max = hf − φ, where φ is the work function. This confirmed light's particle nature.
Sodium (φ = 2.3 eV) with 400 nm light (3.1 eV): K = 0.8 eV.
Electrons ejected from deeper levels have less than K_max.
In more detail
Einstein's photoelectric equation states that the maximum kinetic energy of ejected electrons is KEmax = hf − φ, where φ is the work function of the metal.
Real-world uses
- Photoelectric measurements determine Planck's constant.
- Photodetectors are designed using this equation.
- Engineers designing photodetectors use Einstein's equation to predict the maximum energy of electrons ejected by a given light.
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Frequently asked questions
What is the work function?
The minimum energy needed to remove an electron from the metal surface.
Why can electrons have less energy?
Some lose energy on the way out of the metal before escaping.
What is the work function?
The minimum energy needed to remove an electron from the surface of a metal.
Related topics in Quantum Mechanics
Planck's quantum hypothesis · Planck's constant · Photoelectric effect · Threshold frequency · Stopping potential · Photon momentum