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Why is Light an EM wave?

Physics Asked by Boingboingboing on June 1, 2021

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?

One Answer

There are two main ways for photons to be emitted:

  1. Accelerating charges (as you have mentioned); and
  2. 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.

Answered by Ali on June 1, 2021

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