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Compton scattering
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Photon–electron collision conserves energy and momentum.
Δλ = h/mc(1−cosθ)A photon scattering off an electron loses energy and its wavelength increases by Δλ = (h/mₑc)(1 − cosθ). Conservation of energy and momentum explains it with the photon as a particle.
Maximum shift of 2.43×10⁻¹² m at 180°.
The effect needs short wavelengths such as X-rays.
In more detail
In Compton scattering, a photon collides with an electron and loses energy and momentum, changing its wavelength. This result confirmed that light has momentum.
Real-world uses
- Medical imaging and radiation physics use Compton scattering to model X-ray interactions.
- Detectors in astronomy use Compton scattering to measure gamma rays.
- Compton scattering experiments showed that light has momentum, because photons lose energy and change wavelength when they strike electrons.
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Frequently asked questions
Why does the wavelength increase?
Because the photon transfers some of its momentum and energy to the electron, lowering its frequency.
Does light really have momentum?
Yes. The photon momentum is h divided by its wavelength.
Why does the wavelength change?
The photon transfers momentum and energy to the electron, so the scattered photon has a longer wavelength.
Related topics in Momentum & Collisions
Ice-skater spin · Kepler's second law from L · Collision of particles in physics labs · Newton's cradle · Momentum of light · Radiation pressure