Question

A photon collide a electron at rest find the energy after collision

Answer 1

If a high energy photon interacts with an electron, the interaction can be described by ... As a specific example, consider a 10GeV photon in a head-on collision with an electron at rest.

Answer 2

Some of the energy and momentum is transferred to the electron (this is known as the Compton effect), but both energy and momentum are conserved in this elastic collision. After the collision the photon has energy hf/ and the electron has acquired a kinetic energy K.