In two separate setups for a Biprism experiment using the same wavelength,fringes of equal width are obtained. If the ratio of slit separation is $2:3$,then the ratio of the distance between the slit and the screen in the two setups is:

An oil film flowing on water appears coloured due to interference. For observing this effect,the approximate thickness of the oil film should be:

$A$ transparent film of refractive index $2.0$ is coated on a glass slab of refractive index $1.45$. What is the minimum thickness of the transparent film to be coated for the maximum transmission of green light of wavelength $550 \ \text{nm}$ (in $\text{nm}$)? [Assume that the light is incident nearly perpendicular to the glass surface.]

$A$ thin transparent film with refractive index $1.4$ is held on a circular ring of radius $1.8 \ cm$. The fluid in the film evaporates such that transmission through the film at wavelength $560 \ nm$ goes to a minimum every $12 \ seconds$. Assuming that the film is flat on its two sides, the rate of evaporation is . . . . . . $\pi \times 10^{-13} \ m^3/s$.

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 a biprism experiment is immersed in water,and the fringe width in air is $\beta_a$,find the new fringe width if the refractive index of the biprism material is $1.5$ and the refractive index of water is $1.33$.