# How does photoelectric effect prove that light is also a particle?

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.

• What do you mean, "particle?" The photoelectric effect proves that light delivers discrete quanta of energy, and it proves that the amount of energy in each quantum is a function of the wavelength. In other words, you can count photons. That sounds very particle-like, but it is not proof that photons bear any other resemblance to your idea of what "particle" means. – Solomon Slow Dec 17 '19 at 15:45
• @Solomon Slow So energy of each quantum is dependant on wavelength/frequency of light, am i right? – user248881 Dec 17 '19 at 15:53
• Yes. I should have said "frequency," because the wavelength can change when a photon passes through different media, but the frequency remains constant. The energy of a photon is $h\nu$ where $h$ is the Planck constant, and $\nu$ is the photon's frequency. – Solomon Slow Dec 17 '19 at 16:03
• related: physics.stackexchange.com/questions/68147/… Note that the two answers contradict each other. – user4552 Dec 17 '19 at 19:21
• @user248881, yes. The ideal laser would emit a beam of coherent light. That is, light in which every photon has exactly the same energy/frequency/wavelength, and in which every photon appears to have come from the same, distant, infinitessimal point. Practical lasers come very close to that ideal. – Solomon Slow Dec 18 '19 at 14:27