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When the photons with enough energy impinge on a photocathode, it emits electrons. Does this mean that the solid will lose all its electron at one point? If not, how are electrons restored?

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possible duplicate of What if all the electrons leave a metal? – John Rennie Aug 27 '14 at 7:05
First part of this question is likely a duplicate. The follow up question may by different. – BMS Aug 27 '14 at 7:16
The follow-up question makes this distinct from the proposed duplicate, so I'm reluctant to vote to close this, but it would be good if you could make the second point stronger and more explicit. – Emilio Pisanty Aug 27 '14 at 11:13
Yes, it is possible to "bleach" or "saturate" a photodetector if the electrons cannot be replenished fast enough. This is (was) a common problem with those ancient tube-based TV cameras. – Carl Witthoft Aug 27 '14 at 11:37

1 Answer 1

When an electron gains enough energy from a photon of light, it can leave the surface of the metal - leaving the metal with a positive charge. But this positively charged piece of metal will attract an electron to become neutral again. Often, if 'left to itself' the photo electron will just fall back to the metal surface it came from.

If there is a positively charged electrode nearby, the electron will go there instead and a sensitive miliameter placed between the metal and the electrode will detect a small current as electrons will flow through the meter to make up the deficit.

There is a delicate balance of charge in nature.

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I think your last sentence is inaccurate (even if limited to Terra vs. the universe as a whole) – Carl Witthoft Aug 27 '14 at 13:18
Yeah, you are right. I wanted to mention the conservation of charge, perhaps that would have been more clear, though less poetic. – mcodesmart Aug 27 '14 at 19:02

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