Ok so for many years, light was thought of as a wave but this couldn’t explain the photoelectric effect. From experiments it was shown that if the light shone on the metal surface was below a particular frequency, no electrons would be emitted from the surface of the metal at all. Wave theory suggests that electrons would be emitted regardless of the frequency, but the rate of emissions would be lower the lower the frequency of light. Thinking of light as a particle explains the observation from the experiment. It is known that a metal has a work function (min energy of a photon incident on the metal surface for photoelectric emissions) the photon energy (hf) has to be equal to or above the work function. A photon transfers energy in a one on one interaction with an electron that allows the electron to leave the metal from the surface. If the photon energy isn’t at least equal to the work function, then no electrons are emitted from the surface of the metal. This therefore demonstrates the particle like nature of light. (Just finished my Physics A level 😂😂 hope this explanation helps)