Imperfections in optical lenses can be observed with the help of

$A$ parallel beam of light of intensity $I_0$ is incident on a coated glass plate. If $25 \%$ of the incident light is reflected from the upper surface and $50 \%$ of the light that enters the glass is reflected from the lower surface of the glass plate, the ratio of maximum to minimum intensity in the interference region of the reflected light is

If Fresnel's biprism experiment is performed in water instead of air,what will be the effect on the fringe width?

$A$ thin film of water $(\mu = 4/3)$ is $3100 \,\mathring{A}$ thick. If it is illuminated by white light at normal incidence,the colour of the film in the reflected light will be:

The colors seen on an oil film floating on the surface of water are due to interference. What should be the order of the thickness of the oil film?

Assertion: Thin films such as a soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light.
Reason: It happens due to the interference of light reflected from the upper surface of the thin film.