Analysis of Newton’s Rings Interference

Abstract

A plano-convex combination lens produces an interference pattern of concentric circles known as Newton’s rings. The objective was to measure unknown properties of the plano-convex lens by using characteristic relationships of Newton’s Rings and thin lenses. Concentric fringes produced by the lens were visually counted, and the radius of the ensemble was measured. This data allowed the radius of curvature to be calculated. To verify this work, a different approach was taken. If the focal length was found using the thin lens equation, the radius of curvature could be calculated. However, the plano-convex lens was not easily focused. It was hypothesized this was due to an extreme focal length, and a two lens system could solve the problem instead. The system contained a lens with known properties and the plano-convex combination lens. It could be used to measure the unknown focal length of the plano-convex lens, and by extension find its radius of curvature. This method was also difficult due to the long focal length. Tiny changes in measured lengths resulted in huge percent differences and occasionally errors. Therefore, it was difficult make accurate comparisons for verification. Nevertheless, the research was valuable, and it was found in a publication that Ophthalmologists apply the same method of counting concentric Newton’s rings to visually check for astigmatism and calibrate prescription lenses.