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B Does a charge radiate only when changing direction?

  1. Apr 19, 2016 #1
    They say that an electron accelerating radiates and loses energy, and that is one of the reasons why an electron cannot orbit a nucleus:

    - 1) does a charge accelerating in a straight line radiate, and what is the rate of radiation? do we have to supply extra Ke (apart from m/2 v^2) when we accelerate an electron?

    - 2) Ke in the ground state of hydrogen is 13.6 eV, what energy per second should we supply anelectron to keep it in orbit,? I tried to apply the formula at wiki, but I get 1 Tera eV
  2. jcsd
  3. Apr 19, 2016 #2


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    None. The electron in the ground state is already in a stable orbital and cannot drop down any further. Note that classical E&M rules don't apply at the atomic level. For that you need Quantum Mechanics.
  4. Apr 19, 2016 #3
    I am referring to the classical model, of course. I'd like to know how much extra energy is necessary to compensate the bremsstrahlung.

    My main question, anyway, concerns an accelerating charge in a straight line, does it radiate?
  5. Apr 19, 2016 #4


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    Why not?
    Fast charged particles can be brought to a halt when they enter a solid mass and they release high energy radiation. That would involve 'linear' (negative) acceleration over a very short time (/ distance). I can't think of a mechanism that would produce positive acceleration with as high a value - except in nuclear reactions. But that would instantly take you into the realms of non-classical Physics.
    But you seem to be requiring an 'unhealthy' mix of Classical and QM, which usually means tears before bed time. :smile:
  6. Apr 19, 2016 #5
    No, I am simply asking what happens when you accelerate (not decelerate) an electron.
    Also, I am asking, if a charge circles a nucleus with 13.6 eV Ke , how much energy is needed to compensate bremsstrahlung. According to Larmor formula it should exhaust its Ke in 10^-11 seconds., but I think it is naive to multiply 13.6 by 10^11. That's how I got 1 Tera eV. Did you get that?
  7. Apr 19, 2016 #6


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  8. Apr 19, 2016 #7


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    There is no difference. It's the same thing in different frames.
  9. Apr 19, 2016 #8
    It seems like you are confusing energy and power. Larmor formula gives a radiated power, not an energy.
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