Glossary / History of physics
Compton effect
The increase in wavelength of X-rays scattered by electrons. It showed light colliding with electrons as a particle carrying momentum.
In 1923 Arthur Compton measured that X-rays scattered by matter come out with longer wavelengths depending on the scattering angle, and showed that this is calculated exactly as a billiard-ball collision between a photon and an electron[1].
The photoelectric effect had shown light's energy coming in packets; this experiment showed the packets carry momentum too, and it was decisive in winning acceptance for light quanta. It earned the 1927 Nobel Prize in Physics.
Related terms
- Light quantumThe particle-like packet of energy that light behaves as. Now called the photon.
- Photoelectric effectThe ejection of electrons from a metal when light shines on it. The energy of each electron depends on the light's frequency (colour), not its intensity.