Sir Joseph John Sir Joseph John ThomsonThomson

The Nobel Prize Winning The Nobel Prize Winning Physicist Who Physicist Who Discovered the Discovered the

Electron!Electron!

The Aim of My The Aim of My InvestigationInvestigation

The aim of my investigation, as The aim of my investigation, as many of you will be aware, is to many of you will be aware, is to prove that the atom is built up of prove that the atom is built up of many, even smaller parts. I intend many, even smaller parts. I intend to model my experiments on the to model my experiments on the theories of such great physicists theories of such great physicists as Michael Faraday, Richard von as Michael Faraday, Richard von Helmholtz and Jean Perrin.Helmholtz and Jean Perrin.

The only problem was, that no-one had yet found a way to do this. I know that if a conductor surrounds the path of the ray, the electric field will not affect it. Yet it seemed that even when there appeared to be no conductor in the vicinity, the ray continued on its path, apparently unaffected by the electric field.

It occurred to me that maybe the gas in the tube has been acting as a conductor. Since I had not heard any evidence to the contrary, I decided to try and remove the gas from the tube.

The Apparatus I UsedThe Apparatus I Used

This is the equipment that I decided to use. I removed all the gas, to create a vacuum inside the tube. You can see the electrodes on the diagram, the top is the anode, the bottom is the cathode. In the bulb, you can see the plate which phosphoresces when a cathode ray comes into contact with it, so I can use this to calculate the change in the angle of the cathode ray.

When considering the problem of how to investigate this, I realised that the key lay in the behaviour of a cathode ray passing through an electric field. I realised that if I could prove that these were indeed particles moving in a line, then I could prove that the atom contains small negative particles.

Anode

Cathode

I predicted that I would find that I predicted that I would find that the cathode ray would bend. If the cathode ray would bend. If this was the case, this would this was the case, this would prove that cathode rays are in prove that cathode rays are in fact particles moving in a straight fact particles moving in a straight line. I would find out whether or line. I would find out whether or not they had been bent if they not they had been bent if they changed position when there is an changed position when there is an electric field.electric field.

My PredictionMy Prediction

My ResultsMy Results

This is a demonstration of the experiment that I did, and the results which I obtained.

As You can see, when the electric field is active, the cathode ray bends towards the positive anode. This suggests that it is a negative particle.

My ConclusionMy Conclusion

I conclude, therefore, that the atom I conclude, therefore, that the atom must contain small, negatively must contain small, negatively charged particles, my hypothesis charged particles, my hypothesis now, is that the particles, which I will now, is that the particles, which I will call corpuscles, must be floating in a call corpuscles, must be floating in a cloud of positive charge with no cloud of positive charge with no mass, like a plum pudding.mass, like a plum pudding.

A Brief ChronologyA Brief Chronology

Born in December 1856, died in august Born in December 1856, died in august 1940.1940.

In 1884, at the age of 24, he became In 1884, at the age of 24, he became professor of physics at trinity college, professor of physics at trinity college, Cambridge.Cambridge.

His continuing investigations into His continuing investigations into electrons earned him a Nobel physics electrons earned him a Nobel physics laureate in 1906, and knighthood in laureate in 1906, and knighthood in 1908.1908.