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The electron was discovered in 1895 by J.J. Thomson in the form of cathode rays, and was the first elementary particle to be identified. The electron is the lightest known particle, which possesses an electric charge. Its rest mass is Me equal> 9.1 x 10 -28 g, about 1/1836 of the mass of the proton or neutron. The charge of the electron is -e = -4.8 x 10^-10. The sign of the electron's charge is negative by convention, and that of the equally charged proton is positive. This is somewhat an unfortunate convention, because the flow of electrons in a conductor is opposite to the conventional direction of the current. The most accurate direct measurement of e is the oil drop experiment conducted by R.A. Milikan in 1909. In this experiment, the charges of droplets of oil in air are measured by finding the electric field, which balances each drop against its weight. The weight of each drop is determined by observing its rate of free fall through the air, and using Stokes' formula for the viscous drag on a slowly moving sphere.
Approximate Word count = 614
Approximate Pages = 2.5
(250 words per page double spaced)
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