Photoelectric Effect

The photoelectric effect is the emission of electrons from a material when it absorbs electromagnetic radiation such as ultraviolet light, with the ejected electrons called photoelectrons. Albert Einstein explained the effect by proposing that light travels as discrete energy packets, later called photons, rather than as a continuous wave, work that helped establish the quantum nature of light. Electrons are dislodged only when the light exceeds a certain frequency regardless of its intensity, a result classical wave theory could not explain. The effect underlies electronic devices built for light detection and precisely timed electron emission, and is closely related to the photovoltaic and photoconductive effects used in solar energy technology.