Newton’s Ring Apparatus is a fascinating experimental setup used in the field of interferometry. Let me explain its components and purpose:

1. Principle:

   • Newton’s Rings are an interference pattern observed when monochromatic light (such as from a sodium lamp) passes through two glass surfaces: a plano-convex lens (one side flat, the other curved) and a flat glass plate.
   • When these surfaces are pressed together, they create a thin air film between them.
   • The interference between the reflected and transmitted light waves produces a series of bright and dark concentric circular rings.

2. Apparatus Components:

   • Sodium Lamp: Provides monochromatic light.
   • Plano-Convex Lens: The curved surface faces downward, creating the air film.
   • Flat Glass Plate: Rests on the lens and forms the other part of the air film.
   • Microscope: Positioned vertically above the glass plate to observe the interference pattern.
   • Traveling Microscope with Micrometer: Used for precise measurements of ring diameters.

3. Observations:

   • When viewed through the microscope, you’ll see alternating bright and dark rings.
   • The central dark spot corresponds to zero path difference (constructive interference), while the bright rings represent increasing path differences.

4. Applications:

   • Wavelength Determination: By measuring the diameter of the rings, you can calculate the wavelength of the incident light.
   • Refractive Index Measurement: The spacing between rings depends on the refractive index of the air film.
   • Quality Testing of Optical Surfaces: Newton’s Rings reveal imperfections in optical surfaces.

5. Specifications:

   • Magnification: 10X
   • Micrometer Travel: 25 mm
   • Least Count: 0.01 mm