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

$A$ parallel coherent beam of light falls on a Fresnel biprism of refractive index $\mu$ and refracting angle $\alpha$. The fringe width on a screen at a distance $D$ from the biprism will be (wavelength $= \lambda$).

$A$ thin film of thickness $t$ and refractive index $1.33$ is coated on glass with a refractive index of $1.50$. What is the minimum thickness $t$ required for strong reflection when light of wavelength $600 \, nm$ is incident normally?.......$nm$

In a biprism experiment using sodium light $\lambda_1 = 6000\, \mathring{A}$,an interference pattern is obtained in which $20$ fringes occupy $2\, cm$. On replacing sodium light by another source of wavelength $\lambda_2$ without making any other change,$30$ fringes occupy $2.7\, cm$ on the screen. What is the value of $\lambda_2$ in $\mathring{A}$?

Light is incident on a glass plate $(\mu = 1.5)$ such that the angle of refraction is $60^\circ$. $A$ dark band is observed corresponding to a wavelength of $6000 \, \mathring A$. If the thickness of the glass plate is $1.2 \times 10^{-3} \, mm$,find the order of the interference band.

What is the shape of the interference fringes formed on the screen due to a point source $P$,in the case shown here?