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I'm currently studying Electromagnetic Optics, and I don't quite understand the (classical) process through which we perceive an object with a given color. From my understanding, I'd make a distinction between transparent and absorbent mediums:

  1. Transparent mediums: we see the light that goes through them, and the rest of it is absorbed. Problem: does this mean the mediums have a resonant frequency for every single color except red? I've consulted this post, and although it is quite illuminating (pun intended), it doesn't answer my question.

  2. Absorbent / Opaque mediums: we see the light they reflect, not the one they transmit. Problem: do they reflect what they absorb?

Please explain this in terms of resonant frequencies, if possible

Qmechanic
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AlanFox86
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  • The following has a lot of good discussion about color perception: https://physics.stackexchange.com/q/777501/ – Matt Hanson Mar 23 '24 at 14:32
  • I wouldn't say "see color" in the title, as it implies a biology, when the question is about $T, A, R$ in the spectrum. – JEB Mar 23 '24 at 15:00

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When light hits an object, it may be reflected, transmitted, or absorbed. Each photon undergoes one of these.

There is more than one way to change the fraction of incident light that gets each outcome. Here is some information about that. If we repeatedly divide a colorful solid in half, at what point will the color disappear?

In everyday objects, the most common way light becomes colored is through absorption. Absorption can happen as light travels through an object. Suppose half the red light is absorbed in a given thickness. Two thicknesses would absorb another half, leaving $1/4$ of the original intensity. Red light decays exponentially with thickness. At the same time, blue light might be absorbed less quickly. The same thickness might absorb $1/10^{th}$ of the light. Blue light also decays exponentially, but at a slower rate. Light becomes bluer and bluer as it progresses. You can see this in water. A few meters below the surface, red objects look black because there is no red light left for them to reflect.

Absorption can happen very quickly at a surface, such as colored paint or a piece of copper. In copper, light does not penetrate much more than a wavelength into the metal. Copper can be made into an extremely thin sheet by depositing copper vapor onto a glass substrate in a vacuum. These can be partially transparent.

mmesser314
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