$A$ 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?.......$nm$

$A$ light of wavelength $5890 \; \mathring{A}$ falls normally on a thin air film. What is the minimum thickness of the film such that the film appears dark in reflected light?

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 $\mathring{A}$?

In a biprism experiment, the distance between $4^{th}$ and $13^{th}$ bright band on the same side is '$y$' when light of wavelength $6000 \text{ Å}$ is used. For a light of wavelength '$\lambda$' the distance between $6^{th}$ and $16^{th}$ bright band on the same side is again '$y$'. The value of '$\lambda$' in $\text{Å}$ units is

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.

Assertion: Thin films such as a soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light.
Reason: It happens due to the interference of light reflected from the upper surface of the thin film.