The charge to mass ratio, e/m |
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The charge to mass ratio e/m for the electron (or any other charged particle) can be determined by accelerating moving electrons (cathode rays) at right angles to a uniform magnetic field of known strength, B. Remembering that for a circular path in a perpendicular magnetic field, the centripetal force is given by mv2/r, gives.... ... where r is the path radius. The energy of the electron is given by ... ... where V is the accelerating (anode) voltage of cathode-ray tube. Combining the two equations to eliminate the unknown velocity gives.... |
| The original work, with a home made cathode ray tube, was carried out in1897, by JJ Thomson, in Cambridge, England. |