. P HOTOELECTRIC E FFECT . . Hertz’s observations The phenomenon of photoelectric emission was discovered in by Heinrich Hertz ( - ), during his electromagnetic wave experiments.
In his experimental investigation on the production of electromagnetic waves by means of a spark discharge, Hertz observed that high voltage sparks across the detector loop were enhanced when the emitter plate was illuminated by ultraviolet light from an arc lamp. Light shining on the metal surface somehow facilitated the escape of free, charged particles which we now know as electrons. When light falls on a metal surface, some electrons near the surface absorb enough energy from the incident radiation to overcome the attraction of the positive ions in the material of the surface. After gaining sufficient energy from the incident light, the electrons escape from the surface of the metal into the surrounding space.
. . Hallwachs’ and Lenard’s observations Wilhelm Hallwachs and Philipp Lenard investigated the phenomenon of photoelectric emission in detail during - . Lenard ( - ) observed that when ultraviolet radiations were allowed to fall on the emitter plate of an evacuated glass tube enclosing two electrodes (metal plates), current flows in the circuit (Fig.
. ). As soon as the ultraviolet radiations were stopped, the current flow also T ABLE . W ORK FUNCTIONS OF SOME METALS Metal Work function Metal Work function - 00000 (eV) - 00000 (eV) Cs .