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We know that when the intensity of incident light increases, number of photoelectrons ejected increases irrespective of the frequency (assuming it to be greater than threshold frequency. But does it depend on frequency too in some situations like in case of high frequency or something?

Aditi Narware
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  • I think it might happen in the case of semi-conductors. If the frequency is quite high, it might result in breakage of bonds, which will cause ejection of more electrons than predicted. I am suggesting this because Si-Si bonds are quite weak (coming in at 52 kcal/mol) and light with wavelength in the region 200 Angstrom is enough to break it. – ShankRam Feb 21 '16 at 16:47

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The number of photoelectrons per incident photon doesn't really vary with photon energy (frequency). Particularly a photon won't eject multiple "photoelectrons." By definition a photoelectron is a loosely bound electron (i.e. not in an atomic or molecular orbital) which is ejected in a one-to-one basis by a photon and thus satisfying the equation $$ \rm{KE}_{electron} = \rm{h}\nu - \phi$$ where:

  • $ \rm{KE}_{electron}$ is the kinetic energy of the electron
  • $\rm{h}\nu$ is the energy of the incident photon
  • $\phi$ is the work function for the substrate (how much energy it takes to remove electron from substrate).

In general the substrate would be a metal and the electron would be in the metallic (electrically conducting) layer.

  • If the electron is bound in an atomic or molecular orbital then the technique is Electron Spectroscopy for Chemical Analysis (ESCA).
  • If the photon is too energetic then it penetrates too deeply to eject an photoelectron.

The gist of the above conditions is that photoelectrons are created with relatively low energy photon just above the needed threshold given by the work function, $\phi$.

Another aspect of this is that a photon can only interact with one electron at a time. However if the photon is greater than $2\phi$ in energy it is possible that the electron can receive enough energy to knock yet another electron out of the metal. These two electrons wouldn't be "photoelectrons" since they don't fit the equation. They would be noise in the experiment and the experiment would need to be designed to minimize counting such electrons. So the ejection of multiple electrons by a photon is possible, but not multiple photoelectrons by definition.

MaxW
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