Can I Change Frequency to Increase Ejected Photoelectrons?

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Discussion Overview

The discussion revolves around the relationship between the frequency of electromagnetic radiation and the number of ejected photoelectrons in a photoelectric cell, as well as the calculation of voltage based on the number and kinetic energy of these electrons. The scope includes conceptual understanding and technical reasoning related to the photoelectric effect.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether changing the frequency of electromagnetic radiation can increase the number of ejected photoelectrons.
  • Another participant suggests that increasing the intensity of the radiation is necessary to increase the number of ejected electrons, while noting that more energetic photons increase the energy of the ejected electrons but not their quantity.
  • A different participant argues that increasing the frequency can indeed increase the number of emitted electrons, citing the threshold frequency and the absorption of photons.
  • There is a repeated inquiry about how to calculate the voltage of a photoelectric cell given the number of ejected photoelectrons and their kinetic energy.
  • One participant explains that the maximum kinetic energy of photoelectrons can be predicted using the work function and discusses the concept of stopping potential, suggesting that a photoelectric cell functions more as a current source than a voltage source.
  • Concerns are raised regarding the practical utility of a simple photoelectric cell based on the conditions required for operation.

Areas of Agreement / Disagreement

There is disagreement regarding the effect of frequency on the number of ejected photoelectrons, with some participants asserting that frequency can increase the number while others maintain that intensity is the key factor. The discussion on calculating voltage remains unresolved, with multiple inquiries but no definitive answers provided.

Contextual Notes

Participants reference concepts such as threshold frequency and work function, but the discussion does not resolve the assumptions or definitions related to these terms. The practical limitations of a photoelectric cell's operation are also noted but not fully explored.

brainyman89
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1-if we want to increase the number of ejected photo-electrons, can we change the frequency of the electromagnetic radiation?

2-if i calculated the number of the ejected photo-electrons and the kinetic energy of each electron, how could i then calculate the voltage of this photoelectric cell?
 
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For 1 -you need to increase the intensity, not the frequency. More energetic photons will increase the energy of the ejected electrons, but not the number.
 
what about the second question: if i calculated the number of the ejected photo-electrons and the kinetic energy of each electron, how could i then calculate the voltage of this photoelectric cell?
 
Actually, increasing the frequency of the incident radiation Will increase the number of electrons emitted. The threshold frequency is the frequency at which the least bound electrons are released. Many of the incident photons will not release a photoelectron but be absorbed. If you increase the frequency then a proportion of the incident photons will actually release electrons which wouldn't have been released by light with the threshold frequency. Einstein's Graph of Photon Energy vs Electron KE shows just the Maximum energy and there will be a distribution of energies up to that value.
 
then how could i then calculate the voltage of a photoelectric cell if i calculated the number of the ejected photo-electrons and the kinetic energy of each electron?
 
Not sure what you mean by that.
You can predict (assuming you have an accurate value for the Work Function) the maximum KE of photoelectrons. This is usually measured in terms of 'stopping potential', which is the (negative) potential that a nearby catcher plate needs to be given in order to stop a current flowing in the cell.
I think a simple photoelectric cell could be looked upon more as a current source, once the photoelectrons have started to be emitted, than as a voltage source. I don't think that a simple cell,based on the Einstein experiment would be a useful source of electrical energy - particularly as you need a pristine, clean surface on your Potassium Photo Cathode.
 

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