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Does visible light contain energy?

  1. May 26, 2013 #1
    I read that Infra red waves that are absorbed are emitted by objects. And that makes sense.

    But then I read that it apparently works differently in the visible light spectrum, i.e. the visible light colors we see are only those that that aren’t absorbed, i.e. they’re only the ones that are reflected off the surface of an object. So if red, orange, yellow, green, blue, indigo, and violet color waves reach an object that’s painted red, the red is reflected off the object, and all the other colors are absorbed.
    Wouldn’t that violate the laws of conservation? Isn’t that energy? If it’s energy, how could it keep going in there and never come back out?
     
  2. jcsd
  3. May 26, 2013 #2

    Nugatory

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    Leave a black object out in bright sunlight for a few hours.... Then touch it. It will be hot. That's where the energy it absorbed has gone.
     
  4. May 26, 2013 #3

    sophiecentaur

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    There is nothing different about the energy in light and the energy in IR. If you expose an object to the concentrated (optical) rays of the Sun for a while, its temperature may get so high that it starts to get red / white hot. It is radiating light energy, having absorbed light energy.
    The actual wavelength of the radiated EM, depends upon the temperature.

    Given long enough, an object will reach equilibrium temperature with its surroundings - when the rate of energy absorption equals the rate of emission. If you took an object and placed it in a perfectly reflecting sphere, along with a filament lamp, that object would end up glowing at the same temperature as the filament. This model is a bit flawed, the way it's stated because the filament temperature would rise uncontrollably without some control of the power supply because no energy would escape from the sphere, but it makes my point.
     
  5. May 27, 2013 #4

    CWatters

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    What sophiecentaur said.

    Plants convert some of the energy into chemical energy.
    Solar panels convert it to electricity.
    Most objects just heat up a bit and re-radaite the energy in the infrared part of the spectrum.

    PS: Have a think about planet earth. It absorbs quite a lot of light energy from the sun and has done so for billions of years. Where has the energy gone?
     
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