- This experiment was conducted by J.J. Thomson (Sir Joseph John Thomson) in the year 1897.
- This experiment proved that atom is made up of fundamental particles which are much smaller than the smallest atom 'hydrogen'
- This experiment helped to discover electron.
- According to J.J. Thomson, the cathode rays consisted of very light, small and negatively charged particles.
- He named the particles "corpuscles" which were later known as electrons
- A cathode tube ray was taken in which there were 2 electrodes i.e. Anode(+ve) and the cathode (-ve).
- The tube was filled with an inert gas.
- There was a vacuum pump in the tube.
- High voltage (5000v-10000v) was allowed to flow through the system.
- It was observed that when the gas was at 1atm(atmospheric pressure) no change was seen in the tube. When the pressure was decreased inside the tube, the tube started glowing.
1) A thin metal foil was placed between the 2 electrodes.
Observation: The metal foil started to glow due to heat.
Conclusion: This beam of ray was made up of high energy particles.
2) An object was placed between the 2 electrodes.
Observation: A sharp shadow was formed on the anode.
Conclusion: The beam of rays were travelling from cathode to anode.
3) A light weight paddle wheel was placed between the 2 electrodes.
Observation: The paddle started rotating.
Conclusion: The beam contains high energy particles, which on striking the paddle wheel rotates it.
4) An external electric field was placed.
Observation: The beam of light deflected towards the positive plate.
Conclusion: Particles of the beam are negatively charged.