Brian Cox
It was here in Cambridge that the first clear evidence the smaller objects inside the atoms was found.
Many of the great scientists of history walk this street and one of the greatest was J.J. Thomson who became the director of this, the old Cavendish Laboratory.
In eighteen ninety six, Thomson had just got his hands on this new piece of kit. It’s essentially a particle accelerator. When this plate’s heated, particles are emitted. They are accelerated by these electrodes, they pass through these two plates, across which you can apply a voltage, and they hit the end of the bulb here on screen, which glows so we can see the beam.
And this is modern version of Thomson’s apparatus. Again we’ve got the particle accelerator and there is a screen in there so we can see the beam glow. What Thomson did was he varied the voltage across the plates and he measured the amount of bending as the voltage changed. That allowed him to deduce the mass of the particles in the beams.
The lightest particle known in Thomson‘s days was the hydrogen atom. But Thomson found from these measurements that the particles in this beam are almost two thousand times lighter than hydrogen atoms. Thomson had discovered the first subatomic particle: the electron.
J.J. Thomson
The electron owes its practical utility to its smallness. It might parody Shakespeare to say “my use is great because I am so small.”
Professor Frank Close.
The electron was the first discovery of a fundamental particle and it is interesting to realise that more than a hundred years later the electron is still to the best measurements we can do today, a fundamental letter of nature’s alphabet.
Professor John Womersley
We can use electrons as ways to probe materials and look at the structure in electron microscopes or in big machines like this accelerator behind me. Pretty much all of everything we do in the twenty first century depends on understanding the properties of electrons.
Brian Cox
Thomson had discovered that the atom is not the fundamental building block of matter, there are smaller objects inside. So atoms could no longer be thought of as hard, indivisible spheres. But how did the electrons fit inside the atom? Thomson suggested that the atom was something like this muffin with the negatively charged electrons embedded in a positive body.
It would be a student of Thomson’s that proved him wrong.
