Cutoff potential???

[dmitrip]

hello, in the photoelectric effect what is the cutoff potential? the official definition in my textbook is that it is the "smallest potential difference sufficient to reduce the photo current to zero" you guys will probably laugh but that doesn't really make sense to me and I would really appreciate it if somebody could clarify it to me in simpler language.

thanks a lot.

[olgranpappy]

If I remember correctly, one shines light on a piece of metal and, if the frequency is high enough, electrons come out of the metal and their currect can be detected. The electrons come out of the metal at point 'A' with some kinetic energy and they travel to the detection point 'B'. If you put a voltage (potential difference) between A and B you can slow the electrons down. At some point you will eventually get the electrons to stop altogether and there will be no current measured. You can use this type of experiement to measure the work function of the metal.