Millikan’s Oil Drop

Measuring the charge of one electron

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A drop hovers when $qV/d = mg$.
• Millikan found charges are whole-number multiples of e.
• $e = 1.6 \times 10^{-19}$ C; one coulomb is $6.25 \times 10^{18}$ electrons.

Steps

1. A floating droplet
2. Make it hover
3. Count the electrons
4. Always a multiple
5. Electrons in a coulomb
6. Science and honesty