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Quantom Nature of Light

  1. Nov 28, 2007 #1
    1. The problem statement, all variables and given/known data

    The sun's average surface temperature is 6000K. An incandescent light has a temperature of 2500K, and a flouresent light can be considered to have an average temperature of 3500K. Why do neither of these artificial sources of light provide proper light when exposing a colour film designed to be used in sunlight? Why does a xenon flash (6000K) provide proper illumination for the same daylight film.

    2. Relevant equations

    None that I'm aware of. Just theory.

    3. The attempt at a solution

    My answer (short form of course) would be based on my knowledge learned in chemistry. The photons of the flouresent and incandescent lights don't carry enough energy to make the electrons jump. If this is so their can be no light; electrons jumping from orbit to orbit are the reason for the emitted light. This of course is relevant because the higher the temperature the higher the energy. Xenon has 6000K temp and therefore enough energy to get the electrons to jump.

    Note: Looking to confirm the above answer. It may not be correct as I'm not entirely positive as to it's accuracy.

    Another Question

    High-Speed neutrons, in a nuclear reactor, have a velocity of approx 4 x 10^6 m/s. When they approach a uranium nucleus, instead of hitting the nucleus and causing fission ( splitting the atom into two relatively equal parts), they tend to diffract around it. For this reason, the neutrons are slowed down to approx 2 x 10^3 m/s by a moderator, such as heavy water or graphite, so that the fission-producing collision is more likely to take place. Using your knowledge of matter waves, explain why a moderator is necessary to enhance the process of fission. Using your knowledge of elastic collisions, explain how the moderator works.

    Answer: Don't really know to be honest. I would suspect the moderator is necessary because the photons hit the electrons within the moderator and therefore enhance the reaction. Where as a naked nucleus would not have a high percentage of photons hitting the electrons.

    I cant explain how the moderator works except for that instead of having elastic collisions it creates an energy transfer instead. How? Not really sure. Looking for help on this one.

    Another Question

    When monochromatic (single frequency) light illuminates a photoelectric surface, photoelectrons with many different velocities, up to the maximum value, are ejected. Explain why there is a variation in the velocities.

    Answer: Very simply the velocity of the photoelectrons are contingent on the angle of impact of the photons. The photons will not always hit the electrons in the same direction. We can therefore assume the angle at which the electrons travel are different, causing varying velocities.

    Again not sure about the above answer. Thanks guys. Really appreciate it :)
     
  2. jcsd
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