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Millikan oil drop experiment
Intermediate
Measured the charge of one electron.
Charged oil drops suspended between plates (qE = mg) showed all charges are multiples of e, giving e = 1.6×10⁻¹⁹ C.
Radius found by terminal velocity with Stokes' law.
Won the 1923 Nobel prize.
In more detail
In Millikan's oil drop experiment, charged oil droplets are suspended in an electric field by balancing electric and gravitational forces. The measurements showed that charge is quantised in units of e.
Real-world uses
- It provided the first precise measurement of the elementary charge.
- It remains a classic demonstration in physics teaching.
- Physicists in the nineteenth and twentieth centuries used oil drops to measure the charge of the electron.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
What did Millikan measure?
The elementary charge, about 1.6 × 10⁻¹⁹ C.
How did he balance the drop?
By adjusting the voltage until the drop hung motionless between the plates.
Why did the experiment show quantised charge?
The measured charges of the drops were always whole-number multiples of a basic value, which was the electron charge.
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