$A$ biprism experiment is set up as shown. When the upper half area of the biprism is covered with an opaque material,then:

In a Fresnel's biprism experiment,the distance between the source and the screen is $1 \, m$ and the distance between the source and the biprism is $10 \, cm$. The wavelength of light is $6000 \, \mathring{A}$. The fringe width is $0.03 \, cm$ and the refracting angle of the biprism is $1^\circ$. Find the refractive index of the material of the biprism.

The approximate thickness of an oil film required to observe the interference of light (due to which it appears coloured) is .......

$A$ circular planar wire loop is dipped in a soap solution and after taking it out,held with its plane vertical in air. Assuming the thickness of the film at the top is very small,as sunlight falls on the soap film,the observer receives reflected light. What does the observer see?

Light of wavelength $6000 \text{ Å}$ is incident on a thin glass plate of refractive index $\mu = 1.5$ such that the angle of refraction into the plate is $60^{\circ}$. Calculate the smallest thickness of the plate which will make a dark fringe by reflected beam interference.

$A$ thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass plate as shown. The observed interference fringes from this combination shall be