|MadSci Network: Physics|
The Photoelectric Effect is a phenomenon where electrons can be emitted from the surface of a metal when light of a sufficiently small wavelength shines on the surface. Note that the electrons typically only come off when there is an electric field that *pulls* them off!
The atoms stay behind (the nucleus and the rest of the electrons); they do not leave the metal, but they do become positively charged (because they are missing an electron). If this happens many times, and many electrons are pulled off the metal, the metal will gain a noticeable positive charge (because the negative charges have left the metal!). This positive charge will quickly begin to attract *other* electrons to come back to the metal, neutralizing the metal. If you somehow try to prevent this, the charge will keep building up until it is very hard to pull more electrons off in the first place. So the mass of the metal will not change over time -- eventually it will pull back the missing electrons and have the same mass as before.
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