Which two rays interfere in the newtons rings and what about the rays which are reflected from the top of lens

Question

i want to say that rays are reflected from the top of the lens from the inside of the lens then at the interface of the film and lens and then at the interface of lens and glass plate pl tell which two rays actually interfere and what the othere rays do

Answer 1

The optical properties of thin films arise from interference and reflection. The basic conditions for interference depend upon whether the reflections involve 180 degree phase changes.

Thin film anti-reflection coatings greatly reduce the light loss in multi-element lenses by making use of phase changes and the dependence of the reflectivity on index of refraction. A single quarter-wavelength coating of optimum index can eliminate reflection at one wavelength. Multi-layer coatings can reduce the loss over the visible spectrum.

The idea behind anti-reflection coatings is that the creation of a double interface by means of a thin film gives you two reflected waves. If these waves are out of phase, they partially or totally cancel. If the coating is a quarter wavelength thickness and the coating has an index of refraction less that the glass it is coating then the two reflections are 180 degrees out of phase.