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Quantum mechanics on light

  1. Jun 2, 2015 #1
    Why can we see colors? Everyone know that it is because of "reflected" light. But why is the light reflected? I've learned about abortion of light (excitation to higher quantum energy levels) and emission. But I don't know, why and how light is reflected. Please tell me why :-)
  2. jcsd
  3. Jun 2, 2015 #2
    Think about leaves.We see them green.But why we see them green.Cause inside the leaf theres a chlorophyll.Chlorophyll is a system which absorbs every visible light except green.Chlorophyll is a biological system but it contains molecules.So Chlorophyll will be emit green lighto.Thats the why we leafes green.Reflected light means, atoms emit a light wavelenght which it cant be absorb by an electron.I hopw this will be helpfull
  4. Jun 3, 2015 #3
    also it should be noted that we only see certain waves of light as colors (such as the green being reflected by the chlorophyl) because our eyes and brains are designed to interpret this light so that we can see objects that we can physically interact with. For example, Ultra Violent rays of light exist but they vibrate at a frequency that we can not physically interact with, so we had no reason to evolve to see them. hope this gives u a better understanding of color and how we perceive it.
  5. Jun 3, 2015 #4
    There's a few interesting complications too. Your eyes only have 3 color detectors: red, blue and green. Think of an object which emitting pure yellow light, at a wavelength which is in-between green and red. Both the red and green detectors in your eyes will trigger and your brain will think yellow. But if the same object was emitting pure green and also pure red light, your eyes would get the same reading and also think the object was yellow.

    This means that 'color' really only refers to combinations of which of your eye detectors are activated and in what proportion. Real-life objects emit in an enormous range of wavelengths, not just pure red, green and blue.

    I'm not sure this was really your question but it's interesting :3
  6. Jun 3, 2015 #5
    @ArmanCham you say emit. Does that mean, that the atoms actually absorb the ligh? And the when the excited electron fall down to another energy level, it emit the green light - and the rest is emited as heat?
  7. Jun 3, 2015 #6
    Yeah they atoms absorb the light.I want to give an example.Why we see something black ? Cause it absorbs light and we see no color.That energy causes as heat that why people tell us "you should wear black in winter"

    Thats true.Think this way.Light has to come our eyes to see something.Atoms has to emit that radiation (here green light) and then we can see the thing.If atom cant emit light we cant see it.

    I didnt understand quite this part but its true I guess

    you can watch this
  8. Jun 3, 2015 #7


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    One of the things long-time members on here will learn is how to ask a "proper" question. This is because, eventually, they all learn that to avoid lengthy discussion on the nature of the question itself, one has to sit down and think just a bit so that one can frame a question clearly.

    Your original post here is actually a bit vague. What you are actually asking is NOT "why can we see colors" (which is actually a question belonging in the Medical or Biology forum), but rather "why do objects have colors"! Look carefully and think. These are two very different questions! The former deals with the "detector", which is our eyes, while the latter deals with the "source", which is the object that is the "source" of the light. Two entirely different focus, no pun intended.

    The knee-jerk reaction to many here is to focus on "atomic energy level transition". This is wrong because for the color of the objects, SOLID objects, that we see around us, are not governed by such atomic transition. Let me show you how I can falsify that fallacy.

    Let's look at two objects: diamond and graphite. They look very different, both in terms of color and in other physical properties. But yet, they are both made of the SAME element, i.e. carbon.

    If what we see depends ONLY on atomic transition, they both will look the same, because they both are carbon chunks. So the fact that they look different, and they also have very different physical properties, should already tell you that solid properties are predominately due to not the properties of isolated atoms, but rather due to something else. In this case, it is due to how these atoms are arranged, and how they behave collectively as a conglomerate!

    This is why we have solid state physics as an area of study, and why it is different than "atomic" physics.

    Now that I've given you a hint on what to look for, you might want to start by reading the FAQ entry on the speed of photons in a solid. It will give you a start on what makes a solid transparent, reflective, etc.

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