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Homework Help: What property of light does the photoelectric effect display?

  1. Sep 22, 2007 #1
    What property of light does the photoelectric effect display?
  2. jcsd
  3. Sep 22, 2007 #2
    In photoelectric effect electrons are emitted from a piece of metal when light is shining on it. Apparently, light gives some of its energy to electrons, so they can overcome a certain energy barrier that separates metal from the vacuum. The puzzling property was that no electrons were emitted if the light frequency was below certain threshold. The emission was absent even for very high intensity light, which clearly had high total energy. This puzzle was solved by Einstein in 1905. He introduced the idea of photons - particles of light - and received the Nobel prize for his discovery.

  4. Sep 22, 2007 #3


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    Particle theories of light had been around long ago.

    It was Planck, not Einstein, who proposed the idea that light was quantized -- an electromagnetic wave consisted of indivisible components. Quanta are not particles in the classical sense, but there are enough similarities that the nomenclature stuck. Also, things once thought to be (classical) particles have since been found to be quanta, giving even more reason to continue using the word 'particle' to describe quanta.

    One of the things Einstein did was realize that the quantum theory of light explained the photoelectric effect.
  5. Sep 22, 2007 #4
    Yes, the idea of light corpuscles was first proposed by Newton. But it was largely forgotten at the beginning of the 20th century due to successes of the wave theory of light in explanations of such effects as diffraction and interference.

    It is true that Planck explained the thermal radiation spectrum by assuming that energy radiates in discrete chunks - quanta. However, there is some (significant) distance between this idea and Einstein's vision that light is a flow of countable particles - photons. It took many years after Einstein's proposal to understand that the particle nature of light and its wave properties can be reconciled within quantum mechanics.

  6. Sep 24, 2007 #5
    Light of intensity 1.5 x 10 x-2 Wm/2 and wavelength 250 x 10 x-9m is incident on an iron surface of area 1 x 10-4 m2. The iron surface reflects 95% of the light. The threshold frequency for iron is 1.1 x 10x15 Hz.
    1) The intensity of light available for the photoelectric effect
    2) The number of electrons emitted per second
    3) The work function in electron volts for iron
    4) The stopping potential for this radiation

    Could someone answer this question for me showing working used as well.

    Also, to my previous question. It was only worth one mark. So basically the photoeletric effect shows the dual wave-particle property of light.
  7. Sep 24, 2007 #6
    I guess you can say so.

  8. Sep 25, 2007 #7
    Thanks very much.
  9. Oct 5, 2007 #8
    how do i calculate the energy emitted by different wavelengths of light ? is it possible to do an experiment that uses a photovoltaic cell to measure the voltage produce by directing light of different wavelengths ?
  10. Oct 5, 2007 #9
    How to operate a resistance box

    what does the INF mean on a resistor box ?
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