The photoelectric effect is a physical phenomenon where electrons are emitted from a material when it is illuminated by electromagnetic radiation, such as light. This effect demonstrated that light energy is not transferred continuously but rather in discrete packets, known as quanta or photons. Classically, it was difficult to explain how the energy of the emitted electrons depended solely on the frequency of the incident light and not its intensity. Modern understanding confirms that the kinetic energy of the emitted electrons is proportional to the frequency of the incident radiation, while the existence of a cutoff frequency dictates the minimum frequency required to overcome the material's work function—the minimum energy needed to liberate an electron. This effect was fundamental in establishing the quantum nature of light and the particle-wave duality of electromagnetic radiation.