Undergrad What were the real results of the photoelectric effect experiment?

[pkc111]

TL;DR

I am confused about information regarding the effect of light frequency on photocurrent in the Lenard's apparatus.

Pearson Physics 12 states:
"When the light sources have the same intensity but different frequencies, they produce the same maximum current"

However, Phet Simulation Photoelectric Effect seems to show that photocurrent changes with light frequency (eg see below for different photocurrents at 179 nm and 414 nm incident light wavelengths on sodium:

 

[jedishrfu]

Khan Academy has a good description of the experiment and results found

https://www.khanacademy.org/science/physics/quantum-physics/photons/a/photoelectric-effect

 

[Drakkith]

Khan Academy has a good description of the experiment and results found

https://www.khanacademy.org/science/physics/quantum-physics/photons/a/photoelectric-effect

Hmmm. That page doesn't appear to be in line with the PhET simulation, as it says that the electric current is proportional to the intensity of the light, not the frequency, whereas the PhET simulation has current increase as both intensity and frequency increase.

 

[jedishrfu]

I found this old thread in the PF basement circa 2011 on this sim and why there is some confusion over its results. Perhaps @ZapperZ can respond as he did then about it.

https://www.physicsforums.com/threads/fatal-error-in-computer-simulation-photoelectric.492766/

 

[vanhees71]

Ironically in almost all treatments in physics books (even at the university level) in
$$\hbar \omega=E_{\text{kin}}+W_B$$
for the famous experiment by Millikan with the stopping voltage the constant $W_B$ is quoted wrongly as the binding energy of the electrons in the cathode, rather it's the binding energy of the anode [1]. To establish this, by the way, took Millikan years, while the measurement of Plancks constant $h=2 \pi \hbar$ was pretty right from the very beginning.

[1] J. Rudnick, D. Tannhauser, Concerning a widespread error in the description of the photoelectric
effect, Am. J. Phys. 44, 796 (1976).
https://doi.org/10.1119/1.10130

 

[ZapperZ]

Ironically in almost all treatments in physics books (even at the university level) in
$$\hbar \omega=E_{\text{kin}}+W_B$$
for the famous experiment by Millikan with the stopping voltage the constant $W_B$ is quoted wrongly as the binding energy of the electrons in the cathode, rather it's the binding energy of the anode [1]. To establish this, by the way, took Millikan years, while the measurement of Plancks constant $h=2 \pi \hbar$ was pretty right from the very beginning.

[1] J. Rudnick, D. Tannhauser, Concerning a widespread error in the description of the photoelectric
effect, Am. J. Phys. 44, 796 (1976).
https://doi.org/10.1119/1.10130

Actually, even that is not as clear-cut.

The nature of what a "work function" is is more complicated than such a simple answer. For example, in many instances, it is treated as simply the image charge potential of an electron emitted very near the surface of the material, thus creating an image charge of itself. The work function then is the minimum energy for this electron to overcome the image potential of itself.

See, for example, Pg. 10 of this article, which is a common usage of work function in accelerator physics and photoinjectors:

https://indico.cern.ch/event/218284...ts/352241/490774/Part_1_-Electron_sources.pdf

It is why one can modify the work function via Schottky effect, resulting in a lower work function and thus, higher electron emission and higher QE.

Zz.