Millikan Oil-Drop Experiment – Experimental Set-Up

PCS 125   Physics: Waves and Fields

Robert Millikan measured e, the magnitude of the elementary charge on the electron
He also demonstrated the quantized nature of this charge
Oil droplets pass through a small hole and are illuminated by a light
With no electric field between the plates, the gravitational force and the drag force (viscous) act on the electron
The drop reaches terminal velocity with Fd=mg
When an electric field is set up between the plates
The upper plate has a higher potential
The drop reaches a new terminal velocity when the electrical force equals the sum of the drag force and gravity