Millikan’s Oil-Drop Experiment can accurately determine the charge of a single electron. The major body of the experiment is a small flat-plate electric field. We initially have many little oil droplets randomly move in the electric field. Shortly ionize the air in the electric field to have the droplets carry various charges. Observing the speed of motion of the oil droplets, we can calculate the charges in each droplet and deduce the quantity of a single charge. This research rewarded Robert Millikan the Nobel Prize in Physics in 1923.
  

Microscope
To observe the motion of the oil droplets in the chamber and measure the velocity.

Oil Chamber & Uniform Electric Field
Oil chamber with a parallel
pair of horizontal metal plates
inside.
A hole  was cut into the
chamber to allow the droplets to
spray into the uniform
electric field.

Light Source
It’s more convenient for us to observe the oil droplets through a microscope with a light source.

Atomizer
To spray the tiny oil droplets into the chamber.

High-voltage Source
By applying a potential difference across the plates, a uniform electric field was created between them.

Video

Millikan’s Oil-Drop Experiment

Department of Physics (Digital Archive Project of NTU General Physics Laboratory)
National Taiwan University