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Photoelectric Effect (Concept)

  1. May 8, 2015 #1
    The kinetic energy of a photoelectron is independent of the intensity of the light.

    If we increase the intensity of the light, the effect is, the number of photons arriving will increase and in turn we will eject more photoelectrons. However, the maximum kinetic energy of any one photoelectron is unchanged.

    So then even at low-intensity, we can eject electrons as long as the frequency of incident light is greater than the work function (required energy to eject electron).

    So if we want photoelectrons with more energy, we simply require photons of higher frequency.


    This is where my confusion arises. What does it actually mean to increase the intensity versus increase the frequency? The intensity is the amount of energy transmitted while frequency is the number of oscillations per unit time. In my head, it makes sense that if we increase the energy, we will increase the number of oscillations, which in turn increases the kinetic energy of the photoelectron. So obviously I am having troubling differentiating intensity and frequency.
  2. jcsd
  3. May 8, 2015 #2


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    Staff: Mentor

    Intensity can have several different meanings when it comes to light and optics, but in this example it just means that the number of photons per second is increased. Increasing frequency changes the 'color' of the light.

    That depends on what you mean by 'increase the energy'. If you increase the energy per photon, the frequency has increased. If you increase the energy delivered by the light per second, either the intensity could have increased (photons/second) or the frequency could have increased while the number of photons per second remains the same.
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