Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Radiation from accelerated charge

  1. Sep 2, 2011 #1
    If a charge undergoes acceleration it emits electromagnetic radiation.

    Where does the energy associated with this radiation come from?

    Thank you very much
  2. jcsd
  3. Sep 2, 2011 #2

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    The charge recoils against the radiation and slows. Another way to look at it is that it is harder to accelerate a charged object than an equivalent neutral object.
  4. Sep 2, 2011 #3
    Whatever has accelerated the charge has put energy into it to get it going. An external force does work, the charge gains kinetic energy, then gives off some of this kinetic energy as radiative energy and slows down in the process.

    Think of a circular particle accelerator speeding up small bunches of protons along its circular track. Energy from the electrical power grid is transferred into the electromagnetic control fields used to accelerate the protons. The protons then emit some of that energy as radiation.
  5. Sep 2, 2011 #4
    So then in undergradaute texts, when your given a proton in an external electric field, and asked to find the speed of the proton after some time t, technically you can not use kinematic equations and assume the acceleration will be the field times charge divided by mass, as it should be loosing some of its kinetic energy simultaneously as it is accelerating.

    Obviously we shouldn't even tackle this with classical mechanics.
  6. Sep 2, 2011 #5
    well the accelerating will be that from the field, but its speed will be affected by some other deceleration which accounts for the lost kinetic energy too
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook