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

When a mica sheet of thickness $7 \ \mu m$ and refractive index $\mu = 1.6$ is placed in the path of one of the interfering beams in a biprism experiment, the central fringe shifts to the position of the seventh bright fringe. The wavelength of the light used is $............ \ \mathring{A}$.

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

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 $\mathop A\limits^o$?

$A$ very thin transparent film (like a soap bubble) is viewed in white light. The color of the film appears .......

In Fresnel's biprism experiment,on increasing the prism angle,the fringe width will