Newton Rings
Overview: A convex lens is placed against a flat plate and illuminated with white or monochromatic light. Concentric rings appear as the result of thin film interference in the air wedge between the two elements.
Supplies: Newton ring apparatus – 2 glass plates in a frame with 3 adjustment screws, monochromatic light
Objectives: View the interference rings and how they change by adjusting the 3 screws.
Setup:
- Place the ring demos on the table
- Turn off the room lights
- Turn on the monochromatic light
How to run the demo:
- Adjust the knobs to adjust the sizes of the rings
What’s Happening?
Waves reflecting from two surfaces can interfere constructively and destructively. In the Newton ring demo, light waves are being reflected at glass/air and air/glass interfaces. The interference produces a concentric ring pattern of rainbow colors in white light, or dark and light rings in monochromatic light.
This phenomenon can be explained through thin film interference. The glass pieces in the apparatus are pressed together, with one convex glass piece and the other flat. There exists a thin film of air between the two glass pieces, which has a thickness of zero where the two glass pieces touch, but then increase the further away from the point of contact it is. Adjustment screws are tightened to secure intimate contact at the center.
Learn more: (external links)