Newton's Rings
Definition and meaning of Newton's Rings in chemistry.
Newton's rings are an interference pattern created by the reflection of light between two surfaces, typically a spherical convex surface and an adjacent flat glass surface. This optical phenomenon manifests as a series of concentric alternating bright and dark circular fringes.
In more detail
When a convex lens is placed on a flat glass plate, a very thin film of air is trapped between them, with a thickness that gradually increases moving away from the central contact point. Light reflecting from the top and bottom boundaries of this air layer undergoes constructive and destructive interference depending on the thickness. The varying thickness of the air gap results in the recognizable circular ring pattern, which can be utilized to test the uniformity and curvature of precision optical surfaces.
Key facts
| Field | Physical Chemistry |
|---|---|
| Mechanism | Thin-film interference |
| Appearance | Concentric bright and dark circular fringes |
Placing a plano-convex lens on a flat glass slide and illuminating it directly with monochromatic sodium light will produce a clear set of Newton's rings.
Frequently asked questions
Why is the central spot of Newton's rings dark in reflected light?
The central spot is dark due to a phase change of half a wavelength that occurs upon reflection at the denser glass boundary, causing destructive interference at the point of contact.