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I learned that EM waves are caused by the movement of charges (e.g. electrons), because they have an electric field and the change in the particle's position doesn't update the field instantly all over space but propagates at the speed of light.

With the same reasoning I also learned that thermal radiation is caused by the random movement of particles in any object with temperature > 0K.

So if I wave my hand at 3hz (with all the charged particles in it) am I producing an ELF radio wave? Is it that the energy of this wave (low frequency, low amplitude) is just to low to produce any effect? Or is there something wrong in what I've learned?

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    $\begingroup$ Essentially, yes. You're also producing even weaker gravitational waves. $\endgroup$
    – Javier
    Commented Aug 13, 2015 at 18:23
  • $\begingroup$ @Javier really? $\endgroup$
    – TanMath
    Commented Aug 13, 2015 at 19:18
  • $\begingroup$ Not the movement, the acceleration of charges induces a magnetic field and this induces a electric field and so on. So your hand is a radio wave source as long as the hand is accelerated (including negativ acceleration). So rotating your hand around induce a EM radiation too. $\endgroup$ Commented Aug 13, 2015 at 20:46
  • $\begingroup$ @HolgerFiedler if a charged particle is moving at a constant speed, but in a gravitational field of Earth (e.g. car on a road), would this count as an accelerating charge and therefore would this also produce EM waves? $\endgroup$
    – TKN
    Commented May 10, 2021 at 17:36

2 Answers 2

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In short, yes, but very weakly.

Long answer: Ordinary matter (like your hands) is composed by atoms, molecules, or ions aggregates (e.g., table salt). Since the lowest energy state of these systems is charge-neutral, it is energetically favorable that any piece of ordinary matter reaches a charge-neutral state. However, your hands can still have a very small, spurious charge imbalance. As a consequence of that, waving your hands can produce very, very weak EM radiation (and perhaps gravitational waves, as Javier has pointed out). Just notice that the contributions to the EM radiation of the huge number (multiples of the Avogadro number) of electron and protons in your hand cancel each other over a very short distance, and in practice a net EM radiation is produced only if the net electric charge of your hands is non zero. Of course you can increase the magnitude of the EM radiation by increasing the electric charge of your hands (don't try this at home).

This cancellation does not occur in the case of gravitational waves. By the way, I think that for this reason, the gravitational waves produced by your hands are stronger than the EM radiation in natural units, that is, if the physical units of measurement are set such that the gravitational and electromagnetic coupling constants are $G=\alpha=1$.

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  • $\begingroup$ don't try this at home??? Where are you recommending trying it? $\endgroup$
    – deworde
    Commented Jan 12, 2016 at 15:52
  • $\begingroup$ I was obviously kidding $\endgroup$
    – sintetico
    Commented Jan 12, 2016 at 19:31
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No.

Firstly, as it has been noted in the answer by @syntetico, the net electric charge of hands is zero, i.e., moving one's hands creates no electric current, and consequently no source term in the Maxwell equations.

Secondly, even if one holds a charged object in hands (or somehow caused charge imbalance on one's hands), these charge oscillations will not result in propagating waves, due to the impedance mismatch with the environment where these waves have to propagate. The rule of thumb for creating propagating waves is using antenna that is about half-wavelength long. For 3Hz waves one's hadns are too short, whereas for having wavelength comparable to the extent of one's hands one needs to wave them with a Megahertz frequency.

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