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  Hertz, Hallwacks and Lenard's observation on Photoelectric effect Hertz observation The phenomenon of photoelectric emission was discovered by Heinrich Hertz in 1887, when he was working with his electromagnetic wave experiment. When suitable radiations fall on a metal surface,some electrons near the surface observe enough energy from the incident radiation. Due to it, they are able to overcome the attraction of the positive ions in the material of the surface and escape to the surrounding space. Hallwacks and Lenard’s observation Hallwack and Lenard made a detailed study of the Photoelectric effect during 1886 to 1902. They observed,” when ultraviolet radiation falls on an emitter plate that is positive plate electrons are emitted from it which are attracted towards the other metal plate called collector plate kept at positive potential.The flow of electrons through the evacuated glass tube results in the current flow in the external circuit.  Thus light falling on the surf...