Compton Scattering

A water wave "scattered" from a floating cork will have the same frequency and wavelength as the incident water wave.

In 1923 A H Compton conducted a series of experiments investigating a phenomenon that bears his name, Compton scattering. In these experiments, shown schematically below, Compton scattered X-rays from various materials. He found that the scattered X-rays had longer wavelengths than the incident X-rays. Further, as the scattering angle phi increased, so did the wavelengths. Using the ideas of Einstein's photoelectric effect, this meant the X-ray photons lost energy during the collision with the electrons in the metal. Compton found excellent agreement between his experiments and the quantum nature of light with ordinary conservation of momentum and energy. The scattered X-rays bounced off the electrons much like billiard balls and the relationship between their energy and their frequency (or wavelength) was, again,

E = h f

Sir Isaac Newton had thought light was made of tiny particles he called "corpuscles". Young's famous double slit experiment had shown conclusively, however, that light was a wave, not a particle. (Maxwell had shown that visible light and X-rays are really the same--EM radiation). Millikan and Compton had shown, just as conclusively, that light was made of particles we now call "photons".

Things were getting curiouser and curiouser.

Photoelectric Effect

deBroglie Waves
Return to Ch 28, Quantum Mechanics

(c) Doug Davis, 2002; all rights reserved