Further support for the photon model from electrons, changing magnetic waves comes form Compton scattering in which x-rays scater form electrons, changing direction and frequency in the process. Classical electromagnetic wave theory cannot explain the change in frequency of the x rays on scattering, butthe photom model can. Suppose and `x`-ray photon is moving to the right. It has a collision with a slow-moving electron, as in figure. The photon transfers energy and momentum to the electron which recoils at a hight speed. The x-ray photon loses energy, and the photon energy formula `E=hf` tells us that its frequency must decrease. The collision looks very much like the collision between two particles.

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