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I have now encountered various explanations on how matter interacts with electromagnetic waves (EM) but it still seems like an unconnected mess. The best way I can demonstrate my questions is with an example: White light is shone on a red object. But what is white light exactly? I have read that it is a collection of all visible light but how can white light be a collection when it is an electromagnetic wave? Does that mean that white light is the sum of all visible lights? Nonetheless, when the wave is shone on a red object, apparently three things can happen:

  1. It gets reflected (like on a mirror)
  2. It gets through unhindered (like on a window)
  3. It gets absorbed

I am interested in the third case. But my question is, is all energy of the EM absorbed by the electrons and then only the EM of the red color is emitted? Does that not mean that the electrons will gain more and more energy so that it eventually gets ionized? What I have also heard is, that electrons only absorb EM of the red color and then emit them by excitation and relaxation and the other EMs go unhindered. Does that not mean that "behind" of the red object (lets pretend that the object is very thin) all EM without the EM of the red color is emitted? Either way the EM of the red color is then emitted and it will receive our retina so we can interpret it as red. (At least that I understood)

I thank you in advance for answering.

shar
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1 Answers1

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What is white light exactly?

White light can be described as a collection of electromagnetic waves or a collection of photons (at an elementary level the two descriptions are equivalent). In either case, the defining characteristic of pure white light is that the many different wavelengths of the waves or photons that it contains cover all of the visible spectrum with roughly equal proportions of each wavelength.

Is all energy of the EM absorbed by the electrons (in the atoms of a red object) and then only the EM of the red color is emitted?

Yes, more or less. To be precise, the emitted or reflected light in the visible part of the spectrum will contain a preponderance of those wavelengths that our visual system interprets as the colour red.

Does that not mean that the electrons will gain more and more energy so that (the atom) eventually gets ionized ?

No, because electrons also emit electromagnetic radiation in non-visible parts of the spectrum, such as infra-red.

Does that not mean that "behind" of the red object (lets pretend that the object is very thin) all EM without the EM of the red color is emitted?

If you take thinner and thinner slices of any material, fewer and fewer of the photons in any light that falls on it will be absorbed because there are fewer atoms along its path for each photon to interact with. So more and more photons pass straight through the material, and a thin enough slice will appear more or less transparent.

gandalf61
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