I had an argument with my Physics teacher. I know that light has been clearly proven to be a wave, because of the diffraction experiment with the slits. BUT my teacher kept arguing that it is a particle. But his proof states the Photoelectric effect... OK. I searched the internet but to no avail... My previous understanding of the Photoelectric Effect is that, when radiation (i.e. light), it excites the electrons, By transferring energy to the electron, thus the electrons have enough energy to escape. But how does this show that it is a particle?