Newton’s rings
- The series of concentric light and dark colored bands, between two pieces of glass.
- One glass is convex and the second glass is flat.
- 1st glass convex side on flat glass, thus air exists between them.
- Main phenomenon caused by interference of light waves.
- The formation of Newton's ring at air exists in a plano-convex lens and a flat glass.
- Using nearly monochromatic light from a sodium source and determining the radius of curvature of the plano-convex lens.
Apparatus requirement
Using nearly monochromatic light/source of sodium light.
A Plano-convex lens.
An optically flat glass plate.
A Convex lens.
A traveling microscope.
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Plano-convex lens - LGlass palate – G
Parallel beam of monochromatic light normal incident on between G and L. Part of each incident ray is reflected from the lower surface of the lens and after reflection through air film between the lens and the plate.
It reflected back by the plate surface
These two reflected rays causeto produce system of dark and bright color rings with point of contact between the lens and the plate as the center.
The rings known as Newton’s rings,In normal incident themonochromatic light, path different reflected rays it nearly equals to
- reflective index
t - thickness of air-film between the lens and plate glass
The way reflected air to the glass surface introduce phase shift of.
= diameter of nth ring
Procedure
- Level the traveling microscope with its axis vertical. Focus the microscope on the air-film. For will Clearly see Newton's rings.
- Adjust the glass plate for maximum visibility of the Newton's rings. Orientation is at 45o to beam of light
- Move the microscope to the right of the central dark spot.