By deflecting cathode rays with a magnetic field, J.J. Thomson was able to measure the charge-to-mass ratio (e/m) of electrons. Specifically, he determined how much the path of the cathode rays (which are streams of electrons) bent under the influence of known electric and magnetic fields. Using the degree of deflection and the strength of these fields, Thomson calculated the ratio of the electron's charge to its mass. This was a crucial step because it showed that cathode rays were composed of particles much lighter than atoms and carrying a negative charge, leading to the discovery of the electron as a fundamental subatomic particle
. In summary:
- The deflection of cathode rays by a magnetic field allowed Thomson to find the charge-to-mass ratio of electrons.
- This ratio was found to be constant regardless of the cathode material, indicating electrons are universal components of atoms.
- The measured charge-to-mass ratio was about 1.76×1011 C/kg1.76\times 10^{11},\text{C/kg}1.76×1011C/kg, showing electrons have a very small mass compared to their charge
