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How does light show particle properties?

  1. Jan 3, 2009 #1
    Hi everybody,

    There is some things which i can't digest it.In light(gamma or X-ray) detectors we just get tick...tick..tick.......tick from detectors,But In the light interference we see pattern(which it is continuous).Wow....how is it possible if you consider same light source for two case!
    What hapends for light which show to different behavior?

  2. jcsd
  3. Jan 3, 2009 #2

    Doc Al

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    Crank down the intensity and you'll see that "continuous" pattern being built up tick by tick.
  4. Jan 3, 2009 #3


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    Also consider the "photo-electric" effect. Shining a low intensity light on a photo-electric cell will give no effect at all until, as you increase the intensity, a certain threshold of intensity is reached. A then no increase in the current until you hit twice that that intensity, etc. The intensities required depend upon the wavelength of the light. I believe that was, historically, the first indication that light came in "quanta".
  5. Jan 3, 2009 #4

    Doc Al

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    I wouldn't put it that way. If the frequency of the light is below the needed threshold, you can increase the intensity all you want and still get nothing. And if the frequency is above the threshold, even a low intensity light will produce photoelectrons.

    Nonetheless, you are correct that the photoelectric effect is another demonstration of light's particulate nature.
  6. Jan 11, 2009 #5
    Thanks for your replies.So are you saying me in fact light has particle nature wich it shows wave behaviors classically (in large scale)?
  7. Jan 11, 2009 #6


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    Er... this post may be relevant with regards to the "particle" properties and the photoelectric effect:


    I would say that there are two extremely strong type of evidence for the "particle" nature of light: the which-way experiment, and the photon antibunching experiment.

    Unlike the standard, naive photoelectric effect, there are no classical, SED-type attempt at describing those two phenomena.

    We also must be very careful in clarifying that the "particle" of light that we are talking about here has nothing to do with the classical particle, where a particle has definite spatial boundary, etc. The particle of light here only implies that the energy comes in discrete amounts and not divisible. So at a beamsplitter, it has to choose to go one way, or the other, but not both, thus, a which-way situation.

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