BY: JON, MAGGIE, TOM, DENTON

JJ Thompson &The Cathode Ray Tube

Info

JJ Thompson Born December 18, 1856Admitted to Owens College at age 14, later studied at

Trinity College, CambridgeBecame a professor of physics41 years old at cathode ray discoveryWon a Nobel prize for his work on electricity and

gases in 1906Also credited with the discovery of the electron and

isotopes, invented the mass spectrometer, discovered the natural radioactivity of potassium, and that hydrogen has only one electron per atom

Purpose For Cathode Ray Experiments

To find out if cathode rays were streams of small pieces of atoms and if those parts were negatively charged.

Cathode Ray Tube Set Up

Anodes- electrode through which electrical currents flow into a polarized device

Ions-an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge

Cathode-electrode through which electrical currents flow out of a polarized device

Electric field= applied voltage/distance between plates-distance is how far between conductors

Diagram

Cathode Ray

Once the particles pass through the hole in the anode, they enter a region where you can apply an electric field and/or a magnetic field. The electric field is created by applying a voltage across two metal plates (the deflector plates in the diagram above). The strength of the electric field can be calculated if you know the voltage applied and the distance between the plates:

Equation: E= V/DE= electric field V= Voltage D=

distance

How it Works

When he applied a magnet, the ray bent away from it, and the spectrometer at the other end measured very little energy, showing that the particles have a negative charge.

The particles passing through were electrons, but Thomson did not know that yet.

Conclusion

Found that he couldn’t separate the negative charge from the cathode ray, so some part of the atom has to have a negative charge.

This led to the discovery of the electron later in his life.