Compton effecteffect
A photon hits an electron — like a billiard ball hitting another ball. After the collision, the photon changes direction and loses energy, its wavelength increases. This shift is direct proof that light has momentum, like particles.
How it works
The effect is used in gamma spectroscopy to measure the energy of high-energy photons from the energy of scattered electrons. In astrophysics, Compton scattering, including the inverse effect, shapes the X-ray spectra of accretion disks of black holes and pulsars.
💡 The Compton effect convinced the scientific world that light is not only a wave but also a stream of particles; this brought Compton the Nobel Prize in 1927.
\Delta \lambda = \frac{h}{m_e c}(1 - \cos\theta)
Δλ is the change in photon wavelength, h is Planck's constant (6.62607015×10⁻³⁴ J·s), m_e is the electron mass (9.10938356×10⁻³¹ kg), c is the speed of light in vacuum (299792458 m/s), θ is the photon scattering angle.
\lambda_C = \frac{h}{m_e c}
λ_C is the Compton wavelength of the electron (≈ 2.426×10⁻¹² m), a fundamental constant that determines the length scale at which quantum-relativistic effects become significant for the electron.