7A15.10 - Millikan Oil Drop Experiment

Code Number:
Demo Title:
Millikan Oil Drop Experiment
Charge of the Electron
Area of Study:
Modern Physics
Goose Neck Video Camera, Millikan Oil Drop Unit, and Latex Spheres in Solution.

Align the goose neck camera to the eye piece of the microscope so that the scale is in sharp focus.  Squeeze the bulb and introduce a mist of latex spheres into the chamber.  Many bright dots should appear.  Apply the potential voltage to the two plates in the chamber.  Some of the bright dots should appear to move upwards apposing gravity.  Of these that move pick one that is brightest in the microscopes field of view.  By reducing the voltage to zero you should be able to time the dots fall between the lines on the scale.  By applying a voltage you should make the dot move upward at a rate that is proportional to the voltage applied.  This upward motion can also be timed.  The radius for the latex spheres should be on the order of 5.5 X 10-7 m.  With this and knowing the voltage applied, the time to rise or fall the scaled division, the charge of the electron can be calculated.

If done carefully the calculations should come close to the 1.602 X 10-19 coulomb excepted value.

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  • W. Bolton, "2. The Charge on the Electron", Book 3 - Atomic Physics, Physics Experiments and Projects, 1968, p. 5 - 8.

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