1. Robert Millikan Oil drop Experiment~

2. Problems with the previous model (Unknowns)
Scientists at this time believed the atom contains minute bodies that carry a charge called electrons.
Thomson’s cathode ray tube experiments found that the stream of energy had a negative charge and the mass to charge ratio.
Scientists at this time wanted to know:
Magnitude of charge of an electron
If all electrons carry the same charge
Discrete particle

3. Experimental Design
Atomizer would produce small drops of oil in which some would fall through a hole on the upper floor
He would allow to the drop to free fall until it reached its terminal velocity
He would then apply an electrical current to see which drops had a negative charge
The drop would then be analyzed to see how long it took the drop to move up some distance or the energy required to stop it.

4. Oversimplified formula
Charge x Electrical field
Mass x Gravity

5. Oil Drop Experiment

6. Evidence
All electrons carry the same charge “quantized”

7. New atomic model
Thomson experiments did not provide any direct evidence of individual negative particles versus a stream of energy with a negative charge.
Proved electrons are discrete particles with a finite charge (within 2% currently accepted value)
Mass of the electron could be calculated combining Thomson’s and Millikan’s experiments

8. Interesting Facts
Graduate students may have had a greater role in designing the experiment
Excluded outliers from data

9. Websites and other Resources
History
The Prism and the Pendulum by Robert P. Crease
Lab write up for physics
Movie: Interview with Fletcher
Applet