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Shake a magnet fast enough, would i create light?

  1. Feb 20, 2006 #1
    if i were to shake a magnet fast enough, would i create light?,
    and if so which direction would i need to shake it?

    away then towards, up and down or sideways?
  2. jcsd
  3. Feb 20, 2006 #2


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    Move it as slowly as you like and you will create an electromagnetic disturbance - i.e. light. It will propagate in all directions approximately with a dipole distribution.
  4. Feb 21, 2006 #3
    but every time you produce constant velocity state, the radiation pattern will turn off.

    Best regards

  5. Feb 21, 2006 #4


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    Quite correct! I used the word "move" in the context of the OPs term "shake" which implies acceleration.
  6. Feb 21, 2006 #5
    since im making light, does that mean that by moving it im losing energy?
    if so, is it kinda like a (very) slight resistance?
  7. Feb 21, 2006 #6
    You will create an electromagnetic wave when you oscillate the magnet. Light is an electromagnetic wave within a certain frequency spectrum so you'd have to oscillate it at a really high rate and vibrating it that fast would make it fall apart before the frequency reaches light frequency.
    Any direction. Different directions of shakikng will give you different radiation patterns.
    Yes. Its called a "radiation reaction". Its a "self-force" exerted by the magnet on the magnet. Same thing happens with charges when you accelerate them.

  8. Feb 21, 2006 #7
    Self-Force? Would this imply that an accelerated magnet nominally resists further acceleration due to this phenomenon?
  9. Feb 22, 2006 #8
    Yes but not by a significant amount.

  10. Feb 22, 2006 #9
    Thank you. I think I understand it(perhaps a form of self-inductance that resists continuation of the acceleration) yet am somehow fascinated by it. If you or anyone could point me towards specific literature on the subject I would be grateful.
  11. Feb 24, 2006 #10
    See Classical Electrodynamics - 3rd Ed., D.D. Jackson, page Chapter 10. Most of the first part of this chapter deals with accelerating a charged particle and the extra force required to do so due to the creation and emission of radiation and its energy. Same idea that you're intersted in except Jackson addresses an accelerating charge rather than an accelerating magnetic. The ideas are the same. This phenomena is called the Radiation Reaction or Radiation Dampening.

  12. Feb 24, 2006 #11
    Much appreciated. I have a very serious question. Please consider the following scenario:

    Experiment: "Center of Mass Displacement due to the Radiation Reaction Phenomenon"

    I set up two experimental scenarios. In the first, I have two precisely equal non-magnetic masses which are close together then seperated by an accelerating force. In this scenario, the center of mass does not shift. This is my "control"

    In the second, and separate scenario, I have replaced one of the "precisely equal" non-magnetic masses with a comparable mass consisting entirely of, say, a Grade40 neodymium magnet. Then, I separate the NIB mass and the non-magnetic mass by some rapid, accelerating force.

    Under the pretense of "Radiation Reaction", the NIB mass will resist movement slightly more so than the non-magnetic mass, resulting in an end result being a vector-shifting of the center of mass of that "system"

    Pete, is my conceptual experiment correct?
  13. Feb 25, 2006 #12
    Sounds okay so far.
    Any experiment is a correct experiement. Its the analysis that can be correct/incorrect. In your analysis you seem to think that the center of mass of the entire system has changed. It has not. You have neglected to take into account the mass of the radiation into account. When all mass of a closed system is taken into account then the center of mass of that system is conserved.

  14. Feb 25, 2006 #13
    Ah, thanks. I understand now.
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