Momentum of light

  • Thread starter uzair_ha91
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  • #1
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Main Question or Discussion Point

I've read somewhere that only red light is used in photography because of its low energy which does not affect the photographic plate.
So my question is that when light shines on a surface, is momentum transferred to the metal surface?
 

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  • #2
Filip Larsen
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Yes, any surface that reflects, absorbs or emits light will effectively act as if light imparted a very small pressure on it. Reflection, which can be thought of as an absorption followed by an emission more or less back the same way, gives up to twice the pressure. Light (including heat from black-body radiation) emitted from the "the other side" of the surface will of course reduce the effective pressure.

You can look up how solar sails work to see a "practical" application of this effect.
 
  • #3
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I've read somewhere that only red light is used in photography because of its low energy which does not affect the photographic plate.QUOTE]

I hope your not suggesting that film photography cannot photograph something red?
Perhaps the special "red light" used in developing rooms are of such a wavelength that the photographic dyes are not sensitive to.

Thus, I think this has more to do with wavelength sensitivity rather than "energy" levels.

Just my thoughts... could be wrong.
 
  • #4
Char. Limit
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Wavelength is inversely proportional to energy, or something like that.

As an extension of the topic "momentum of light", if you shine light on an object in space, will the object start moving?
 
  • #5
jtbell
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if you shine light on an object in space, will the object start moving?
Solar Sail
 

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