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Double Slit Experiment and it's Results ?

  1. Nov 6, 2014 #1
    Hello all,

    I am just being introduced to quantum physics in my introductory physics course at university and I'm not sure I understand a couple of things...any clarification would be greatly appreciated.

    So, when looking at the double-slit experiment; what can be seen on the viewing screen is an interference pattern consistent with the wave like properties of light...however, when the light passing through the slits is dimmed and the exposure time reduced; the same pattern is not observed and what is seen is a random particle-like pattern...but this is not interpreted as being particles of light hitting the viewing screen but are instead interpreted as evidence to support the idea that electromagnetic fields are quantized...? why? why can't we see this as evidence that light is a particle?

    Also, I understand that energy is quantized...but the concept of what in energy is being quantized eludes me...is it the frequency at which the wave of energy travels? if it is the frequency...aren't higher frequencies of waves just different types of waves? (ex: gamma ray vs. x-rays?) I'm not sure if I make sense but I don't know how else to ask it....thanks in advance for any clarification.
  2. jcsd
  3. Nov 6, 2014 #2


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    Staff: Mentor

    Over time the pattern of individual spots on the viewing screen builds up into the same interference pattern that we see immediately with a more intense source; for an example, look at this sequence of images. There is no way of explaining this behavior with a simple particle model.

    The easiest way of thinking about it (not perfect, but a lot better than thinking of "particles" as little teeny objects travelling between the source and the screen like bullets) is to say that when an electromagnetic wave, be it light, or radio, or infra-red, or ultra-violet, or x-ray, or gamma, interacts with matter, it delivers its energy at single points. The are the individual spots that appear on the screen. The shorter the wavelength and the higher the frequency (that's the only difference between these various forms of electromagnetic radiation) the more energy is delivered each time another spot appears. The total energy delivered is the product of the number of spots and the amount of energy per spot.
    Last edited: Nov 6, 2014
  4. Nov 6, 2014 #3
    Perfect! Thank you so much =)
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