White light is incident at an angle of $30^\circ$ on a soap film with a refractive index of $4/3$. The wavelength of the transmitted light is observed to be $6 \times 10^{-5} \, cm$. Find the minimum thickness of the film.

The thickness of a plate having refractive index $\mu$ which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it is

This question has a paragraph followed by two statements,Statement $- 1$ and Statement $- 2$. Of the given four alternatives after the statements,choose the one that describes the statements.
$A$ thin air film is formed by putting the convex surface of a plano-convex lens over a plane glass plate. With monochromatic light,this film gives an interference pattern due to light reflected from the top (convex) surface and the bottom (glass plate) surface of the film.
Statement $- 1$: When light reflects from the air-glass plate interface,the reflected wave suffers a phase change of $\pi$.
Statement $- 2$: The centre of the interference pattern is dark.

$A$ mixture of yellow light of wavelength $580 \ nm$ and blue light of wavelength $450 \ nm$ is incident normally on an air film of thickness $2.9 \times 10^{-4} \ mm$. The colour of reflected light is

In a Fresnel biprism experiment,the eyepiece is placed at a distance of $120 \, cm$ from the source. The distance between the two virtual images is found to be $0.075 \, cm$. If the eyepiece is moved by $1.92 \, cm$ to cross $20$ fringes in the field of view,what is the wavelength of light in $\mathop A\limits^o$?

What causes changes in the colours of soap or oil films for a given beam of light?