Optics for Optometry

Thin Film Interference A film of thickness from 0.5 to 10  m is a transparent medium of glass, mica, air enclosed between glass, soap film, etc. When the light is made incident on this thin film partial reflection and partial refraction occur from the top surface of the film. The refracted beam travels in the medium and again suffers partial reflection and partial refraction at the bottom surface of the film. In this way several reflected and refracted rays are produces by a single incident ray. As they moves are superimposed on each other and produces interference pattern. Interference in Parallel Film ( Reflected Rays) Consider a thin film of uniform thickness ‘t’ and refractive index   bounded between air. Let us consider monochromatic ray AB is made incident on the film, at B part of ray is reflected (R 1 ) and a part is refracted along BC.At C The beam BC again suffer partial reflection and partial refraction,  the reflected beam CD moves again suffer partial

When light falls on a soap bubble, part of the light gets reflected. Some light enters the bubble and gets reflected from the other side of the bubble surface. Some of the light rays gets refracted. When we look at a bubble, we are seeing all these light rays. Since the bubble film is very thin, the the reflected rays gets a little out of sync with each other. Since the light travels in the form of a wave, this going out of sync causes some of the waves to cancel out or reinforce each other. White light is made up of seven colours with each colour corresponding to a particular wave length. When the light waves cancel out or reinforce, some of the wavelengths gets a boost and some disappears. This gives rise to the colour of the bubble of the colour of an oil film on water. Since the bubble or the film is not uniformly thick, each region of the film produces a different colour. The phenomenon is called interference in physics. The colors of a soap bubble come from white light, whi