Cornus Interference Apparatus

This device is similar to Newton's Rings apparatus, except that an arrangement for loading the test piece is provided for carrying out Cornus interference studies. The objective of this experiment is to determine Poisson's ratio and Young's Modulus for different materials (glass, Perspex etc) using interference method. Weights are positioned at both ends of the bar, causing it to bend longitudinally downward. A glass plate is placed on the bar to produce an interference pattern. By examining the interference pattern, extent of longitudinal and lateral bending can be determined. Thus, Poisson ratio and Young's modulus of the bar can be deduced.

When a plano-convex lens rests on a uniformly bent glass bar, an air film is formed between the two surfaces. Without adding any mass in the weight hanger we get circular rings. But as we uniformly add mass on the weight hangers, the beam bends and we get elliptical fringes.

Experiment:

To study the elastic constants of glass by Cornus interference methods,