Newton’s rings are a classic example of interference of light, formed when a convex lens is placed on a flat glass surface. A thin air film exists between the curved surface of the lens and the flat surface.
Here’s how interference explains the formation of these rings:
- Thin Film Interference:
- Light is partially reflected from both the top surface of the air film (lens side) and the bottom surface (glass plate).
- These two reflected rays interfere with each other.
- Path Difference:
- The thickness of the air film changes from the center outward.
- At certain thicknesses, the path difference between the two reflected rays causes constructive interference (bright rings).
- At other thicknesses, it causes destructive interference (dark rings).
- Circular Pattern:
- Because the air film is symmetrical around the point of contact, the interference fringes appear as concentric circles—these are Newton’s rings.
- Variation with Wavelength:
- The size and spacing of the rings depend on the wavelength of light used.
- Using white light produces colored rings due to interference at different wavelengths.
So, Newton’s rings are a direct result of interference in a varying-thickness air film, confirming the wave nature of light.