Well, the definition of electromagnetic waves in a couple of textbooks is stated to be, 'A wave produced or resulting from the accelerated motion of a charged particle'. My question is straightforward- If it is so, light should not be an EM wave, since photons are not charged. I know that light consists of oscillating electric and magnetic fields,but then there's either something wrong with the definition or my understanding (which is much more probable). Where am I going wrong, folks?
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asked Nov 15, 2020 at 11:19
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2$\begingroup$ Waves on a pond may be due to a rock being thrown in the pond. But waves are not rocks. Likewise, EM waves are produced by accelerated charges, but EM waves are not charges. $\endgroup$– pelaCommented Nov 15, 2020 at 11:33
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$\begingroup$ I am not understanding why photons should be charged to be an EM wave $\endgroup$– amilton moreiraCommented Nov 15, 2020 at 11:34
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$\begingroup$ Read te answer here physics.stackexchange.com/questions/593329/… $\endgroup$– HolgerFiedlerCommented Nov 15, 2020 at 17:53
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1 Answer
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There are two main ways for photons to be emitted:
- Accelerating charges (as you have mentioned); and
- Spontaneous emission when an excited electron drops to a lower energy state.
Electromagnetic waves are defined as propagating waves consisting of orthogonal electric and magnetic fields satisfying Maxwells equations. By this definition, light IS an electromagnetic wave. As I mentioned above, acceleration of a charged particle is not the only way to produce such radiation.
Also just to be clear, photons have no rest mass and no charge. Their energy is purely kinetic. In terms of accelerating charges, the accelerating charge such as an electron or proton induces the EM wave. By your wording you are suggesting that the photon is oscillating and producing the EM wave which is incorrect. The photon can be thought of as discrete packets of energies which are a result of the accelerating electron/proton.
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$\begingroup$ SO basically, it is these electrons and protons which produce the wave and not photons, which are merely constituents of the wave. Is that correct? $\endgroup$ Commented Nov 15, 2020 at 11:56
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$\begingroup$ Correct, it is the accelerated motion of the protons or electrons that causes the wave. Here is a source which explains what I have also said above: andor.oxinst.com/learning/view/article/emission-of-light $\endgroup$– AliCommented Nov 15, 2020 at 12:00