J. J Thomson and the discovery of the electron
The meaning of the following terms should be known before getting into today's session.
Terms:
Cathode - negatively charged electrode.
Anode - positively charged electrode.
Cation - positively charged ion.
Anion - negatively charged ion.
Cathode rays - electron
Discovery:
Cathode-rays tubes are the glass tubes with knob controlling the pressure, low pressured gas is filled inside.
Inside the cathode-ray tube two electrodes are placed.
When high amount of electricity is passed through the electrode. The gas get ionized. Beams of rays emerges from cathode and travels towards anode
The other end of the cathode-ray tube is coated with Zinc sulphide (ZnS). When the the beam of rays hits the coating(due to scattering) it emits light.
So, by this experiment he discovered the cathode rays.
He also tried to find the properties of this cathode rays.
Properties:
1. The cathode rays moves in a straight line.
He placed a opaque object in the glass tube.and he observed the shadow of the object. Therefore he concluded that cathode rays moves in a straight line,
2. Cathode rays get deflected towards positively charged plate.
When Thomson placed a positive and negative electric plates He observed that cathode rays get deflected towards the positively charged plate.
3. Cathode rays get deflected even when a magnets are placed. It deflected towards North pole
The cathode rays also deflected due to the magnetic field.
4. When he kept a rotating fan like structure inside the glass tube, it started to rotate.
So he concluded that electron are fast moving
4. When he kept a rotating fan like structure inside the glass tube, it started to rotate.
So he concluded that electron are fast moving
Conclusion:
He did the above experiment with different electrode and gases. The properties of cathode rays doesn't change.
When he found the mass of the cathode rays, it is smaller than atom. Therefore he felt that this must be a part of atom. The cathode rays moves towards positively charged plate.
He concluded:
1. The cathode rays is composed of negatively charged particle.
2. The mass of the particle is lesser than any atom.
3. These particle can be found in all atoms.
