Overview
The lecture explains Robert Millikan's 1909 experiment to measure the charge of the electron using oil droplets and electric fields.
Millikan Oil Drop Experiment
- Robert Millikan measured the electron's charge at the University of Chicago in 1909.
- He sprayed fine oil droplets into a chamber between two electrically charged plates.
- X-rays were used to ionize air, causing charges to stick to the oil droplets.
- With no voltage, droplets fall based on mass and air viscosity.
- When voltage is applied, negatively charged droplets slow down, stop, or rise depending on their charge.
- By adjusting the voltage and observing droplet motion, Millikan determined charge values.
- All measured charges were multiples of a smallest value.
- This smallest value, 1.6 × 10⁻¹⁹ coulombs, was identified as the charge of a single electron.
Key Terms & Definitions
- Electron — A subatomic particle with a negative electric charge.
- Oil Drop Experiment — Millikan's method for measuring the electron's charge by observing charged oil droplets in an electric field.
- Ionization — The process by which atoms or molecules gain or lose charges.
- Coulomb (C) — The SI unit of electric charge.
Action Items / Next Steps
- Review the procedure and findings of Millikan's Oil Drop Experiment.
- Memorize the fundamental charge of an electron: 1.6 × 10⁻¹⁹ C.