Electrons: Millikan's Oil Drop Experiment

The experimental arrangement of Millikan’s experiment is shown in the figure. the wheel ‘w’ consists of cylindrical blocks made by sodium, potassium, or lithium’s metals are housed in a vacuum to avoid tarnishing. And their surface is kept clean by a cutting knife (k) which could be moved and turned by a magnet outside.
When a beam of light falls on metal, photoelectrons are emitted. These electrons reach electrons will be repelled and only fast-moving electrons will be able to reach ‘e’.the negative potential of electrode ‘c’ increases until the fasten moving current falls to zero. The potential is called stopping potential.
IF ‘v0’ by stopping and.

Here, h, e, f0 are constant so III represents a straight-line equation y=mx+c ‘v0’ is measured from the different values of ‘f’. A graph is then plated between frequency and stopping potential A st lines obtained. The slope of the straight line is.

At the time of Millikan and Fletcher’s oil drop experiments, the existence of subatomic particles was not universally accepted. Experimenting with cathode rays in 1897, J. J. Thomson discovered negatively charged “corpuscles” with a mass of about 1,840 times smaller than that of a hydrogen atom. George FitzGerald and Walter Kaufmann found similar results. In 1923, Millikan won the Nobel Prize in physics in part because of this experiment.

Aside from discerning an electron’s charge, the beauty of the oil drop experiment lies in its simple and elegant demonstration that charge is actually quantized. The experiment has since been repeated by generations of physics students—although it is rather expensive and difficult to do properly.