Question

Give the name of the scientist who discovered the electron. describe the experiment conducted for the discovery of electrons. how are the mass and charge of electrons determined?

Answer 1

J.J. Thomson discovered the electron.

In 1859, Julius Plücker started the study of the conduction of electricity through gases at low pressure in a discharge tube.

Air was almost completely removed from the discharge tube (pressure of about 10^-4 atmospheres). When a high voltage of the order of 10,000 volts or more was impressed across the electrodes, some sort of invisible rays moved from the negative electrode to the positive electrode. Since the negative electrode is
referred to as cathode, these rays were called cathode rays.

The cathode rays consist of material particles that have mass and velocity. These particles carrying negative charge were called negatrons by J.J. Thomson.

The name 'negatron' was changed to 'electron' by Stoney.

In 1897, J. J. Thomson determined the e/m value (charge/mass) of the electron by studying the deflections of cathode rays in electric and magnetic fields. The value of e/m has been found to be $-1.7588\times {10}^8\mathrm{coulomb}/\mathrm{g}.$

The first precise measurement of the charge on an electron was made by Robert. A. Millikan in 1909 by oil drop experiment.

The charge on the electron was found to be $-1.6622\times {10}^{-19}\mathrm{coulomb}.$

Mass of the electron: The mass of an electron is calculated from the value of e/m and the value of e.

$\mathrm{Mass}\mathrm{of}\mathrm{an}\mathrm{electron}=\frac{\mathrm{Charge}\mathrm{of}\mathrm{an}\mathrm{electron}}{\mathrm{Charge}/\mathrm{mass}\mathrm{of}\mathrm{an}\mathrm{electron}}=\frac{-1.6622\times {10}^{-19}\mathrm{coulomb}}{-1.7588\times {10}^8\mathrm{coulomb}/\mathrm{g}}=9.1096\times {10}^{-28}\mathrm{g}$.