Millikan's Experiment

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Millikan's Experiment

Millikan's experiment found the charge and mass of the electron.

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Millikan's oil-drop experiment

  • Robert Millikan performed an experiment that discovered the charge on an electron.
  • Millikan combined his results with Thomson’s specific charge of the electron:
    • This allowed him to discover the mass of the electron.
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Stokes' law

  • Stokes’ law gives the viscous force on a sphere in a fluid.
  • F = 6πηrv
    • F is the viscous force.
    • η is the viscosity of the fluid.
    • r is the radius of the sphere.
    • v is the velocity of the sphere.
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  • Millikan used an atomiser to create a mist of charged oil droplets which fell into a viewing chamber.
  • He then applied a potential difference across the viewing chamber to create an electric field.
  • He could then study the motion of these charged particles in a variable electric field.
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  • By performing the experiment with no electric field, he could see the motion under only the weight of the drop and viscous force.
    • He used the velocity of the particles and Stokes’ law to calculate the radius of the particles.
  • Once the electric field was turned back on, he could adjust the field to hold the droplets still.
    • This allowed him to equate weight to electric field, and hence calculate the charge on each droplet.
  • Each droplet’s charge had a common factor of 1.6×10-19C, which is the charge on one electron.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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