If you guys weren't aware they asked in the AS 2019 to compare photoelectric effect and radiation on LDR. Do you guys think they might ask to compare thermionic emission and photoelectric effect in paper 3?

Reply 27

_gcx

OP

Study Forum Helper

21

Original post by Youreadmyname

If you guys weren't aware they asked in the AS 2019 to compare photoelectric effect and radiation on LDR. Do you guys think they might ask to compare thermionic emission and photoelectric effect in paper 3?

I just know that they're basically the same thing. But with thermionic emission you're using heating instead of photons to reach the work function.

Reply 28

Youreadmyname

11

SimilaritiesAny one from:
●Both must reach a threshold amount of energy/work function to release electrons. (1)
●Both provide the electron with sufficient kinetic energy to escape. (1)
●Kinetic energy of electron will be equal to the energy delivered less the work function in both cases.(1)

DifferencesAny one from:
●Thermionic emission uses internal energy whereas photoelectric effect uses incident photons as energy source.(1)
●In photoelectric effect photons do not reach all electrons whereas in thermionic emission all/more electrons will be absorbing internal energy. (1)
●Varying intensity of light will directly control the number of photoelectrons but not their energy. Varying temperature will affect the energy of emitted thermoelectrons.(1)
●Photoelectrons can be emitted or stopped immediately whereasthermoelectrons may still be emitted while metal cools or have to wait while it is heated.(1)

Original post by _gcx

I just know that they're basically the same thing. But with thermionic emission you're using heating instead of photons to reach the work function.

This is from one of the edexcel resource packs.

OP

Original post by Youreadmyname

SimilaritiesAny one from:
●Both must reach a threshold amount of energy/work function to release electrons. (1)
●Both provide the electron with sufficient kinetic energy to escape. (1)
●Kinetic energy of electron will be equal to the energy delivered less the work function in both cases.(1)

DifferencesAny one from:
●Thermionic emission uses internal energy whereas photoelectric effect uses incident photons as energy source.(1)
●In photoelectric effect photons do not reach all electrons whereas in thermionic emission all/more electrons will be absorbing internal energy. (1)
●Varying intensity of light will directly control the number of photoelectrons but not their energy. Varying temperature will affect the energy of emitted thermoelectrons.(1)
●Photoelectrons can be emitted or stopped immediately whereasthermoelectrons may still be emitted while metal cools or have to wait while it is heated.(1)

This is from one of the edexcel resource packs.

Ah, think I would've only got difference 3, though difference 2 is kind of common sense. Will keep this in mind.

Reply 30

Niice

4

Original post by Youreadmyname

●In photoelectric effect photons do not reach all electrons whereas in thermionic emission all/more electrons will be absorbing internal energy. (1)

How does this work because doesn't the photons for the photoelectric effect reach electrons at different depths in the metal which is what causes the range in kinetic energy? How would this be any different for thermionic emission?

OP

Original post by Niice

How does this work because doesn't the photons for the photoelectric effect reach electrons at different depths in the metal which is what causes the range in kinetic energy? How would this be any different for thermionic emission?

I'm assuming it's because each photon can only interact with one electron, while heat would just cover the surface and be able to give multiple electrons simultaneously enough energy to be emitted? Not sure.

Reply 32

Youreadmyname

11

Original post by Niice

How does this work because doesn't the photons for the photoelectric effect reach electrons at different depths in the metal which is what causes the range in kinetic energy? How would this be any different for thermionic emission?

It's probably to do with the fact that there is a one to one interaction between photons and electrons. So if sufficient energy isn't supplied, the electrons transfer the energy absorbed from the photon to the metal rather than being emitted as a photoelectron. Whereas in thermionic emission the electrons being emitted are delocalized electrons which gain sufficient energy to over come the bonds holding them to the metal.

Reply 33

Niice

4

Original post by _gcx

I'm assuming it's because each photon can only interact with one electron, while heat would just cover the surface and be able to give multiple electrons simultaneously enough energy to be emitted? Not sure.

Original post by Youreadmyname

It's probably to do with the fact that there is a one to one interaction between photons and electrons. So if sufficient energy isn't supplied, the electrons transfer the energy absorbed from the photon to the metal rather than being emitted as a photoelectron. Whereas in thermionic emission the electrons being emitted are delocalized electrons which gain sufficient energy to over come the bonds holding them to the metal.