Photoelectric effect: Saturation voltage

[mgcgian]

TL;DR

Idk, what level, but this is A-levels, so AP physics?

Hi, I just got two inquiries:

My understanding is that the saturation current is reached when the intensity of light is fixed, when the potential difference is at its positive maximum magnitude. Subsequently, whatever kinetic energy store of any photoelectrons, however deep within the metal's surface, will be collected at the anode. Hence, a saturation point is reached, as the rate of emission is now at a constant rate, and now being collected at anode.

What I don't understand is: when a constant current reached, in my textbook, it states that "all the photoelectrons are collected". But, clearly from the graph, if they were to be all collected, wouldn't the voltage decrease.

But in all graphs, they asymptote to a specific value, depending on the intensity of light, showing that not all the photoelectrons are collected.

This leads onto my second, the circuit is complete when photoelectric emission occurs and the electrons are "collected",

so what happens to the electrons, do they flow around the circuit? Do they go to to the anode then go back to the photocathode. The journey of the electron is not really specified.

 

[Baluncore]

Welcome to PF.

Your title "saturation voltage" suggests a maximum voltage. The wavelength of the photons decides the energy and therefore the maximum voltage of a released electron, since the energy of a photon is proportional to frequency.
Energy in eV = 1239.84 / λ nm = voltage.
https://en.wikipedia.org/wiki/Photoelectric_effect#Theoretical_explanation

Saturation current is determined by the intensity of the light, i.e the number of photons that can cause emission of an electron.
https://en.wikipedia.org/wiki/Photo...imental_observation_of_photoelectric_emission

The electrons emitted by the cathode will be collected by an external anode, then will return to the cathode via the voltage source used to set the anode voltage more positive than the photoemissive cathode.

 

[sophiecentaur]

TL;DR Summary: Idk, what level, but this is A-levels, so AP physics?

But, clearly from the graph, if they were to be all collected, wouldn't the voltage decrease.

I'd look at it as a fully charged capacitor - voltage is constant and no current in.

 

[mgcgian]

I'd look at it as a fully charged capacitor - voltage is constant and no current in.

Thanks for the analogy,

 

[mgcgian]

Welcome to PF.

Your title "saturation voltage" suggests a maximum voltage. The wavelength of the photons decides the energy and therefore the maximum voltage of a released electron, since the energy of a photon is proportional to frequency.
Energy in eV = 1239.84 / λ nm = voltage.
https://en.wikipedia.org/wiki/Photoelectric_effect#Theoretical_explanation

Saturation current is determined by the intensity of the light, i.e the number of photons that can cause emission of an electron.
https://en.wikipedia.org/wiki/Photo...imental_observation_of_photoelectric_emission

The electrons emitted by the cathode will be collected by an external anode, then will return to the cathode via the voltage source used to set the anode voltage more positive than the photoemissive cathode.

Thank you for the explanation