Can I Change Frequency to Increase Ejected Photoelectrons?

[brainyman89]

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?

 

[mathman]

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.

 

[brainyman89]

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?

 

[sophiecentaur]

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.

 

[brainyman89]

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?

 

[sophiecentaur]

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.