An interferometer works on the principle that when two waves coincide, the same phases will add to each other while two waves that have opposite phases will cancel each other, assuming both have the same amplitude.
There are varieties of interferometers. Basic working principle for all of them are same though geometry and configuration can be different.
In this section, experiments are performed to determine the wavelength of monochromatic source, refractive index, thickness of transparent films, radius of curvature of lens, Young's and rigidity modulus of the material of the bar, Poisson's ratio of the bar etc. by setting up various interferometers.