Millikan Oil Drop Apparatus

Product Code: AP-8210A


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

  • The experimental principle is straightforward 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 pre-aligned optical system and special condenser to achieve these conditions.

Accuracy in the Oil Drop Experiment depends on the student’s ability to precisely 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.


  • 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 a 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 the apparatus is level.
  • Rod Stand Mounts and Screws: Designed to mount on PASCO’s Large Rod Stand. It 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.
  • 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 the 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.

What’s Included

  • 1x Millikan Oil Drop Apparatus with Switch
  • 1x Non-volatile Oil and Atomizer
  • 1x 12 VDC Lamp Power Adapter

Product Specifications

Maximum Plate Voltage 500 VDC
Light Source Cool LED
Reticle Line Separation: 0.5 mm major divisions; 0.1 mm minor divisions
Plate Spacing 7.62 mm
Plate Diameter 60 mm

Required Accessories

2x Basic Digital Multimeter SE-9786A
1x High Voltage Power Supply SE-9700
1x Banana Plug Cord-Red (5 Pack) SE-9750
1x Banana Plug Cord-Black (5 Pack) SE-9751

Recommended Accessories

Large Rod Base ME-8735
2x 45 cm Stainless Steel Rod ME-8736
USB 3.0 Microscope Camera SE-6204

Replacement Parts

4 oz Bottles of Mineral Oil (Qty. 4) AP-8211
Millikan LED Light Source AP-8212

Also Available

Charge of an Electron Experiment EX-9929A

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