A photon hitting an electron (mass $m$ ) at rest can create an electron-antielectron pair in addition to the original electron. Assume that the two electrons and the positron move away from the collision at rest with respect to each other afterward. What was the photon's initial energy?
A) Zero
B) $m$
C) $2 m$
D) $3 m$
E) $4 m$

Question

Quizplus · Accepted Answer

The initial photon energy must be enough to create an electron-positron pair (energy $2m$) and provide energy for the rest mass of the original electron ($m$), totaling $4m$.

A Photon Hitting an Electron (Mass mmm ) at Rest Can Create an Electron-Antielectron Pair in Addition

A Photon Hitting an Electron (Mass $m$ ) at Rest Can Create an Electron-Antielectron Pair in Addition