Hackaday

A demonstration shows how to recreate J.J. Thomson's 1897 experiment to measure the charge-to-mass ratio of an electron using modern equipment. The setup uses Helmholtz coils to create a magnetic field that traps electrons from a cold cathode tube in a circular path. By measuring the radius and electric field, you can calculate the ratio, which closely matches the accepted value. The experiment requires knowing the electron's charge (determined later by Millikan's oil drop experiment) to derive the actual mass.

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