Let us consider a free electron in space, which is initially at rest. Now let us consider a photon of frequency f, which collides with our free electron giving all its energy to it. This energy will manifest itself as the K.E. of the electron after the collision. Therefore, we can write(adsbygoogle = window.adsbygoogle || []).push({});

hf=(1/2)mv^2 where, h: Planck's Constant

m: Mass of the electron

v: velocity of the electron after the collision

Also, whole of the momentum of the photon will also be transfered to the electron

hf/c=mv

Solving the two equations, we get v=0 or v=2c(which defies special relativity).

Now, v=0 cannot be the solution, as the energy in the electron has to manifest itself in some or the other form, and the only form is K.E. (if I'm not mistaken).

The solution v=2c is not compatible with the fact that c is the ultimate speed.

So, what's the problem?

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Photon-Electron collision problem

Loading...

Similar Threads - Photon Electron collision | Date |
---|---|

An electron emitts a photon and the core is pushed (recoiled) back! | Jul 31, 2013 |

Photon to electron + positron | Jan 21, 2011 |

Opposite beams of photons or electrons | May 31, 2010 |

Electron and photons time of flight | Mar 7, 2009 |

Photon and electron racing show | May 2, 2006 |

**Physics Forums - The Fusion of Science and Community**