In the mid 1800’s scientists successfully passed an electric current through a vacuum in a glass tube. They saw a glow from the tube that seemed to emanate from the negatively charged plate called the cathode. Since scientists didn’t know what the glow was they called it a cathode ray. There was debate over whether the cathode ray was a wave phenomenon like light or a stream of negatively charged particles. JJ Thomson effectively resolved the debate in 1897 by performing a clever experiment that determined the charge to mass ratio of the particles making up the cathode ray. He also showed that this same particle was in all different cathode materials so it must be a constituent common to all atoms. This changed our understanding of the atom from the previous billiard ball model to Thomson’s plum pudding model of the atom.


  1. Why is there no glow when the pressure is higher in the discharge tube?
    and why does the glow again disappear after lowering the pressure below a certain value? It would be great if someone explain it to me , please.

  2. I thought Helium atoms are smaller than Hydrogen. Can anyone confirm this because he said that Hydrogen atoms were the smallest.

  3. can u make a video on .."Which way does Electricity REALLY flow?"
    Electricity flows bcoz of negatively charged electrons? but when we connect a bulb to a battery …both +ve and -ve charge-flow goes in two opposite directions at the same time.   and what happens when a human body get electrocuted??

  4. The cathode filament is heating up and changing shape this is causing the interference pattern, the beam of light is not particles like Thompson states. He simply assumed they are and nobody questioned him. 

  5. Holy cow if my eyes are seeing correctly there is destructive and constructive interference going on in that tube, cannot be particles. Thompson never proved that those where particles in there. Seams to me there is another architecture responsible and its not a particle. The electron is not a particle. 

  6. it reminds me experiment of thermoemission in physics lab. like the force they were talking was a heat emitted because of R of the cathode.