PHOTOELECTRIC EFFECT

phenomenon in which charge particles are released from a material when it absorbs radiant energy. The photoelectric effect commonly is thought of as the ejection of electrons from the surface of a metal plate when light falls on it. In the broad sense, however, the phenomenon can take place when the radiant energy is in the region of visible or ultraviolet light, X rays, or gamma rays; when the material is a solid, liquid, or gas; and when the particles released are electrons or ions (charged atoms or molecules).