The Compton effect, in which X rays scattered by electrons emerge with a longer wavelength, demonstrates that photons
- A. have no momentum
- B. carry momentum and collide like particles
- C. travel slower than light
- D. have mass at rest
Explanation
The scattered photon gives up part of its energy and momentum to the recoiling electron, so its frequency falls and its wavelength rises, exactly as a particle collision would predict. A wave would have been scattered without any change of wavelength. Photon momentum is h divided by wavelength, even though the photon has zero rest mass.
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