phys (0617) - ItI: thomson's experiment

the aim of thomson's experiment was to determine the ratio of charge to mass in cathode rays.

his apparatus was a cathode ray tube with a screen, and he had both an electric field and a magnetic field to focus the cathode rays. with this he found the velocity of the rays, knowing that:

for electric fields:
F = qE

for magnetic fields:
F = qvB

therefore
qE = qvB
v = E/B

when these weren't there, however, he noticed that the rays produced a circular pattern, and he concluded that this was due to a centripetal force.

knowing
F = (mv^2)/r = qE = qvB

he could determine the ratio, ie. m/q

after testing this with different metals in the cathode, he discovered that the ratio was always the same, which proved that the negative particles within the cathode ray were the same for all metals, and later it was concluded that it was the same for all materials.

this was the introduction of the term, electron