Newton's ring device

sodium lamp

Newton's ring principle: The experimental device of Newton's ring is usually a plane made of optical glass with a large radius of curvature (experimental data is 1.2452).

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0.0062m), a wedge-shaped air thin layer is formed between the two surfaces, and the thin layer gradually thickens from the contact point between the convex lens and the plane mirror. When the convex surface is placed downward, when monochromatic light is vertically incident, the convex surfaces of the lens will interfere with each other, and the same interference fringes will be formed where the air film thickness is the same. This kind of interference is called equal thickness interference. Interference fringes are a series of concentric rings with alternating light and dark around the contact point, which are called Newton rings.

Newton's ring is formed because the reflected light from the convex air layer of the convex lens interferes with the reflected light from the air layer on the surface of the glass plate at the intersection, resulting in interference fringes with equal thickness. According to the wave theory, where Newton's ring is formed, the optical path difference between two coherent beams with a thin air layer thickness of d is △d=2d.

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