In a Fresnel's biprism experiment,coherent sources are obtained by which of the following phenomena?

What is the minimum thickness of a thin film required for constructive interference in the reflected light from it (in $ nm$)? Given, the refractive index of the film $= 1.5$, wavelength of the light incident on the film $= 600 \, nm$.

$A$ Fresnel's biprism experiment is performed in water. If the fringe width in air is $\beta_a$,and the refractive indices of the biprism material and water are $1.5$ and $1.33$ respectively,find the new fringe width.

When petrol leaking from a vehicle falls on a rain-wet road,colours are observed. This is due to the.......... of light.

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

What is the effect on Fresnel's biprism experiment when white light is used?