Newton’s Rings

Measuring with a lens and a sheet of glass

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 curved lens on flat glass traps a thin wedge of air.
• Dark rings at $r_m = \sqrt{m\lambda R}$; the centre is dark due to the half-wave flip.
• The rings measure lens curvature or the wavelength of light.

Steps

1. A wedge of air
2. Dark in the middle
3. Measure the curvature
4. Rings crowd together
5. Blue light
6. Find the wavelength