I was watching this experiment (https://www.youtube.com/watch?v=v-1zjdUTu0o) which demonstrates the photoelectric effect, but it does not make any sense to me how it proves light as a particle instead a wave. Can you please explain me? And I also want to know where exactly the electrons that are released by beam of UV light go.
According to the classical theory, light is a wave and this effect would be explained to be due to transfer of light energy on to the Zinc plate. Increasing the intensity should therefore increase the kinetic energy of the ejected electrons.
However, this did not meet up with the experimental observations which showed that light below a particular frequency did not cause any photoelectric effect. Also, increasing the intensity increased the photoelectric current instead.
Einstein then proposed that light behaved as a stream of discrete wave packets called photons which had an energy value associated with them which depended on its frequency. Both observations could be exhaustively explained with this theory.
As shown earlier in the video, the plate is negatively charged which means it has excess of electrons. When hit with UV light, the electrons leave the metal and become dissipated in the surrounding air.