Is the photoelectric effect in a photocell reversible?

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Main Question or Discussion Point

Is the photoelectric effect in a photocell reversible? Suppose both the cathode and the anode of a photocell are from cesium. The anode and the cathode are externally (outside the photocell) connected by a copper wire. Cesium has a threshold frequency of 470 THz. The cathode is illuminated with monochromatic light of frequency 570 THz. Electrons fly from the cathode to the anode without acceleration of deceleration because no voltage source is connected to the anode. Two questions:

1) Does the anode emit light?
2) If the anode emits light: is the frequency of that light monochromatic 470 THz, or is the frequency in a continuous range from 470 to 570 THz?
 

Answers and Replies

  • #2
sophiecentaur
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The situation where an electron arrived at and interacted with the lattice of many atoms with electrons associated with them is not the equivalent of a photon arriving and interacting with a single surface atom. So I can see no reason why the photoelectron would produce light. This is very different from the effect of a fast electron encountering an isolated gas molecule because that situation can transfer all or most of the electrons energy into changing the state of that single molecule / atom and producing ionisation, perhaps.
Sorry - duff sentence at the start of that but I didn't bother to tidy it up as it gives the gist of what I meant.
 
  • #3
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LEDs are sometimes viewed as a sort of reverse photoelectric effect, where a current produces light. When an electron travels across the junction, its excess energy is released as a photon. The threshold voltage of the diode corresponds to the energy of the emitted photon. What is the difference between the junction of the diode and the anode of the photocell?
 
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sophiecentaur
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A difference is that the diode junction is a semiconductor and not on the surface and the Anode is a metal and on the surface. Very little in common.
 
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ZapperZ
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Is the photoelectric effect in a photocell reversible? Suppose both the cathode and the anode of a photocell are from cesium. The anode and the cathode are externally (outside the photocell) connected by a copper wire. Cesium has a threshold frequency of 470 THz. The cathode is illuminated with monochromatic light of frequency 570 THz. Electrons fly from the cathode to the anode without acceleration of deceleration because no voltage source is connected to the anode. Two questions:

1) Does the anode emit light?
2) If the anode emits light: is the frequency of that light monochromatic 470 THz, or is the frequency in a continuous range from 470 to 570 THz?
Your setup has an extremely low probability of emitting light.

However, there is such a thing as an inverse photoemission. This is where electrons (with higher energies than your setup) impinges on a surface, and that process causes the emission of light. The physics is the opposite of photoemission (which is a more general phenomenon than the photoelectric effect). This method is often used in inverse photoemission spectroscopy to study the unoccupied part of the band structure (photoemission spectroscopy probe the occupied side).

And as sophiecentaur has indicated, you should never confuse this with LED's because the process is different.

Zz.
 

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