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Strong light on water?

  1. Dec 13, 2013 #1
    what happens if a high photon density light package was directed to a volume of water for a fraction of a second? what would happen?
    i mean what if the whole sun's light is to be shined from the concave lens (pretend the sun only shines on 1 side) i mean, the frequency isn't much higher, so PHOTOelectric effect wouldn really happen.... but all those photons onto a volume of water (let's presume all photons makes contact) for a millisecond, would the water evaporate and turn into gas exploding?
    is it even possible to energies ATOMS in a small time frame?
  2. jcsd
  3. Dec 13, 2013 #2

    Simon Bridge

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    Same as any light - but more so. Details depend on the type of light.

    Oh that would easily vaporize everything it touches.

    The time scale of the electromagnetic dipole interaction is of order 10-23s ... milliseconds is more like 10-3s.
    Last edited: Dec 13, 2013
  4. Dec 14, 2013 #3


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    There is no such thing. The time scale of the interaction is not a property of electromagnetism, but rather the size of the thing it is interacting with. The oft-quoted 10-23 sec is the time it takes light to travel 1 fermi, and is therefore the minimum time it takes for anything to interact with a nucleon.
  5. Dec 14, 2013 #4

    Simon Bridge

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    Thanks for the clarification. Timescale does indeed depend on the thing under consideration.
    10-18s to cross an atom for eg. we can also talk about the mean-time to ionize a sample given the flux etc etc etc.
    Properly the "size" should be the crossection - which does depend on the interaction.

    ... but OP was talking about the total output from the Sun here so I figured the nuclear interaction oom figure was appropriate here.

    The question before us is whether there is sufficient time for the entire photon flux from the Sun, concentrated on "some water" to "excite the atoms". The point I'm trying to make is that the sort of time thought of as "small" (milliseconds) is actually very large.

    We could ask what would constitute a time period so small that there would be no noticeable effect I suppose.
    I think OP is under the impression that there is a lower threshold time in which nothing would happen.
  6. Dec 20, 2013 #5

    Claude Bile

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    On a millisecond timescale, you probably would not get much happening.

    On shorter timescales though.... look up "ultrafast" or "femtosecond" lasers to see a huge, diverse amount of physics on light propagation through solids/fluids.

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