How does the photoelectric effect provide evidence for a particulate nature of electromagnetic radiation?

The photoelectric effect is light incident on a metal’s surface causing the spontaneous emission of electrons. The classical wave theory of electromagnetic radiation predicted the kinetic energy of emitted electrons was dependant on the intensity, and the number of emissions dependant on the frequency of the incident wave. However, experimental results contradicted these predictions, with the kinetic energy being linearly proportional to the frequency above a threshold value, and the number of emission proportional to the intensity of incident light.The inconsistency between theory and results led Albert Einstein to propose a corpuscular theory of light in 1905, where electromagnetic radiation was composed of discrete packets of light called photons. Each photon carried an energy proportional to the frequency, with the constant of proportionality named Planck’s constant, E = hf. One photon could collide and transfer it’s energy to an electron. Thus, the number of electron emissions from the metal surface was proportional to the number of incident photons, or the intensity of light. Moreover, if the electron gained enough energy to overcome the binding energy to the metal surface, the rest of the energy would be converted to it’s kinetic energy as it escaped. This binding energy is called the work function of the metal, and it explains the existence of a threshold frequency, which represents a photon of energy equivalent to that required to overcome the work function. The energy of the released electron was the difference between the photon’s energy, hf, and the metal’s work function, explaining the linear relationship between kinetic energy and frequency.