Describe the interaction between photons and matter using Compton scattering.

• In Compton scattering, a photon interacts with a free electron. The Compton effect is when a photon that emerges from the interaction has a lower energy and longer wavelength than the incoming photon. The magnitude of the change is related to the direction of the photon after the collision.
• Compton scattering provides evidence that light is a collection of discrete, quantized energy packets called photons.
• Compton scattering can be explained by treating a photon as a particle and applying conservation of energy and conservation of momentum to the collision between the photon and electron.
• The transfer of a photon’s energy to an electron results in the energy, momentum, frequency, and wavelength of the photon changing. Relevant equations:
• The change in wavelength experienced by a photon after colliding with an electron is related to how much the photon’s direction changes. Relevant equation:

AP Physics 2 includes full quantitative and qualitative treatments of conservation of momentum in two dimensions.

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