J.J. Thomson discovered the electron through experiments with cathode ray tubes. He found the mass to charge ratio of electrons and proposed the plum pudding model of the atom, where electrons are embedded in a positively charged material. Robert Millikan performed the oil drop experiment, which measured the minimum electric charge and enabled finding the mass of the electron. Ernest Rutherford conducted the gold foil experiment, which demonstrated that atoms have a small, dense, positively charged nucleus.

1. Students to complete their own notes.

2. English Physicist
Discovered the Electron
- Studied the Cathode Ray Tube
- Found the mass to charge ratio of an
electron
- Led to the Plum Pudding Model

3. The Design of the Cathode Ray Tube

4. So! Thompson has
discovered the
electron, and it must
live inside atoms.
It is much less massive
than the the atom itself,
so perhaps we have
little electrons stuffed
into the ‘rest’ of the
atom like raisins in the
oatmeal, or:
Plum Pudding...

5. American Physicist
Performed the Oil Drop
Experiment
◦ Measured minimum electric charge
that could be carried by a particle
(1905)
◦ This was the charge of the electron
◦ Enabled him to find the mass of the
electron

6. Millikan’s Oil Drop Experiment
Used To Determine the Charge of an Electron

7.  New Zealand born physicist
 Worked with nuclear radiation
 Performed the Gold Foil Experiment
 Discovered the nucleus (1910)
 Discovered the proton (1918)

8. The Gold Foil Experiment
Demonstrated that the atom contains a nucleus
which is:
a. Very tiny – most of the particles missed
b. Positively charged – some were deflected
c. Very dense – some bounced off

9.  Discovered the neutron in 1932
 In college he stood in the wrong line.
He wanted to be a mathematician, but
was in the line for physics and was too
embarrassed to switch.
 Instead he became a famous physicist.

10. End!
The story’s not over, but we’ll pick it up in
chapter 4.