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Measure the charge of an electron to +/-3%

  • Nobel Prize-quality physics in the student lab
  • Includes ionization source for changing droplet charge

Millikan Oil Drop Apparatus



U.S. Educator Pricing

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 Material Safety Data Sheet

Mineral oil
(English – 151 KB –pdf)

 Additional User Resources

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The Millikan Oil Drop Experiment is one of the most popular experiments in undergraduate physics for several reasons:

  • the experimental principle is straight-forward and easy to understand;
  • it measures a fundamental atomic constant using a method that won its originator, Robert Millikan, the Nobel Prize;
  • the observation of the effects of one or more electrons upon oil drops in an electric field provides a striking demonstration of the quantized nature of electricity.

Clear droplet observation and low droplet drift are essential for success with Millikan’s classic experiment. PASCO’s apparatus uses a prealigned optical system and special condenser to achieve these conditions.
Accuracy in the Oil Drop Experiment depends on the student’s ability to accurately measure all the variables involved: plate voltage, plate separation, time and distance of droplet rise and fall, temperature, oil density, etc. Extreme care taken in the design and manufacture of this unit ensures that the student’s best efforts will be rewarded with more accurate results. Typically, a careful student can achieve results within 3% or less of the accepted value.


  • Minimum Electric Field Distortion--A 0.5 mm diameter droplet entry hole in the top capacitor plate has a negligible effect on the electric field.
  • Ionization Source -- The Thorium-232 alpha source can be activated by the switch on the side of the chamber. The source allows the charge on the oil droplets to be changed.
  • Droplet Hole Cover -- Prevents additional droplets from entering the chamber once the experiment has started.
  • Polished Surfaces -- Polished surfaces on the plate spacer minimize absorption of light (and heat) through the chamber walls.
  • Electrical Connection -- Electrical connection to the top plate.
  • Easy Cleaning -- The condenser system easily disassembles for cleaning and inspection.

The Millikan Apparatus mounted on a rod stand for easy eye-level viewing

Oil drops viewed through the option VideoFlex Microscope

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  • Thermistor Connectors -- Attach an ohmmeter to monitor chamber temperature. A thermistor is embedded in the bottom plate of the chamber.
  • 3 Chamber Level Positions: Ionization ON, Ionization OFF, and Spray (allowing air to be displaced when oil droplets are inserted).
  • Droplet Viewing Chamber -- Unique design minimizes droplet drift due to heat from droplet illumination and outside air currents.
  • Viewing Scope -- 30X, bright-field, erect-image microscope with focusing ring.
  • Reticle Focus -- Separate reticle focus and precision etching provide sharp, easy-to-view grid lines with 0.5 mm major and 0.1 mm minor divisions.
  • Plate Voltage Connectors -- Connect a power supply to charge the plates inside the chamber.
  • Plate Charging Switch -- Allows the operator to charge the plates to either polarity or ground the plates. The switch box is separate to minimize vibration
  • Bright 5-watt Halogen Lamp -- Combined with a convex lens and heat reflecting mirror, the droplet illumination system delivers maximum light and minimal heat to the droplet area.
  • Lamp Adjustment Screws -- Position the lamp filament to be focused precisely on the area where the droplets are viewed.
  • Bubble Level -- Bull's-eye level makes sure apparatus is level.
  • Rod Stand Mounts and Screws -- Designed to mount on PASCO's Large Rod Stand. Allows the apparatus to be reduced to eye level.
  • Thermistor Resistance Table -- A convenient table provided for quick conversion of resistance values to Celsius.
  • Focusing Wire -- When placed in the chamber, the focusing wire allows the lamp to be aligned so the light illuminates the center of the chamber, and allows the eyepiece to be focused on the center of the chamber.

Includes Millikan Oil Drop Apparatus, non-volatile oil and atomizer, and 12 VAC lamp power adapter


  • Millikan Oil Drop Apparatus with switch
  • Non-volatile Mineral Oil and Atomizer
  • AC Adapter, 100 - 240 VAC to 12 VDC, 1.0 A
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