People always describe refraction as light stimulating the electrons in the glass, which create their own light, which interferes with the original wave. They always say “the math is too complex, but it’s right.” So I wanted to know what the wave actually looks like. Here is what I was thinking:

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The red wave is the incoming wave. The green wave is what the wave produced by the moving electrons would be. When they add, they create the blue wave, which has a lower wavelength like they describe it. However I still feel like it is wrong.

What does the wave created by moving electrons (green) actually look like?

  • 1
    $\begingroup$ What is the abscissa? The waves can have different wavelengths in the two media, but they can't have different frequencies. $\endgroup$
    – JEB
    Nov 22, 2022 at 19:10

1 Answer 1


The interference is due to a shift in the phase. There is no change in frequency (assuming ordinary refraction, and not another phenomenon such as fluorescence).

An electron bound to an atom can be approximated as a simple harmonic oscillator with a particular resonant frequency. When the incoming wave excites the electron, the electron itself produces an electromagnetic wave. This wave is offset by some phase (which depends on factors such as the resonant frequency of the electron) and consequently interferes with the original wave.

The difference in wavelength is another story. The speed of light in the refracting medium is less than the speed of light in free space. The slower speed results from the absorption and reemission of the wave between atoms. (In fact, the speed of light is the same between atoms and is only slower due to the delay as the electric field interacts with each electron.) Since the frequency of the light is the same, the result is a shorter wavelength.

  • $\begingroup$ So does this mean that the part you explained in paragraph 2 does not affect the speed at all? $\endgroup$
    – gbe
    Nov 23, 2022 at 0:54
  • $\begingroup$ Is it just absorption and re-emission that causes slowing down? $\endgroup$
    – gbe
    Nov 23, 2022 at 17:42

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