By deflecting cathode rays with a magnetic field, J. J. Thomson was able to measure the charge‑to‑mass ratio of the electron, usually written as e/me/me/m.

Quick Scoop: What Thomson Actually Measured

  • In his cathode ray tube setup, Thomson passed the electron beam through electric and magnetic fields.
  • By adjusting the fields until the beam went straight (no net deflection), he could determine the speed of the electrons.
  • Then, using only a magnetic field and measuring how much the beam curved, he derived the value of e/me/me/m, the charge‑to‑mass ratio of the electron.

So, when you see the question:

“By deflecting cathode rays with a magnetic field Thomson was able to measure what property of electrons?”

The expected answer is:

The charge‑to‑mass ratio(e/m)(e/m)(e/m) of the electron.

TL;DR: Thomson’s magnetic (and electric) deflection experiments did not give the electron’s charge or mass separately, but their ratio , e/me/me/m.

Information gathered from public forums or data available on the internet and portrayed here.