1. Newton’s Rings:
Testing the shape of a lens:

2. Mathematical analysis of Newton’s rings is presented in Assignment 11.
- The center is a dark fringe because the path length difference there is nearly zero and there is a relative phase shift of  rad (recall discussion of reflection from a very thin soap film).
- The fringes are not equally spaced -- they are closer together as one moves away from the center. This is due to the thickness of the air film between the two glass plates increasing “faster than linear” because one surface is curved.
(- By contrast, the fringes are equally spaced in a wedge due to flat plates, i.e. the numerical example done in class.)
Mathematical analysis of Newton’s rings is presented in Assignment 11.