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In photoelectric experiment, we always keep the work function constant. It seems to me that as the metal plate loses its negative charge, it may take more energy to pick up an electron off the surface of the conductor.

Is my intuition correct? And if so, does the maximum kinetic energy of photoelectrons decrease with time?

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The energy required to move an electron from inside the metal to outside the metal, work function energy, remains the same but an increasing positively charged metal makes it "harder" for the photo-electron to permanently escape from the metal.
If the photo-electron does not have enough kinetic energy when it escapes it will eventually return to the metal.

One could imagine a situation when the metal has a large enough positive charge such that all the escaping photo-electrons return back to the metal?

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  • $\begingroup$ in the link given as a duplicate, it is said that it may change if we continue to extract electrons. Which one is correct? $\endgroup$ Mar 8 '19 at 16:33
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    $\begingroup$ @physicsguy19 I suspect that there is very little change in any in the work function energy. So as the charge builds up on the plate it still takes the same amount of energy for an electron to escape to just outside the surface. However the guy who gave the answer to the duplicate question is much more knowledgeable than I am so perhaps it is worth asking him? $\endgroup$
    – Farcher
    Mar 8 '19 at 20:48

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