chapter  2
66 Pages

Photoelectric Concept

In 1887, while receiving the electromagnetic waves in an induction

coil with a spark gap generator, Heinrich Hertz (1857-1894)

observed the reduction of maximum spark length when the

apparatus was put in a black box (Hertz, 1887). He noticed that the

spark occurred in the air gap between the two small metal spheres

of the transmitter when ultraviolet radiation was directed at one of

these spheres. The box absorbed such radiation, which helped the

electrons in jumping across the gap. Hertz reported the observations

but did not pursue the experiment further, and also did not make

any attempt to explain them, but others did. In 1897, J. J. Thomson

(1856-1940) showed that electrons are emitted when light falls

on a metal surface (Thomson, 1897). These are now referred to as

photoelectrons (the prefix “photo” refers to the incident light).