Calculate the minimum thickness of a soap film $(n=1.33)$ that results in constructive interference in reflected light, if the film is illuminated with light whose wavelength in free space is $532 \,nm$. (in $\,nm$)

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.

$A$ thin film of water $(\mu = 4/3)$ is $3100 \,\mathring{A}$ thick. If it is illuminated by white light at normal incidence,the colour of the film in the reflected light will be:

$A$ thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass plate as shown. The observed interference fringes from this combination shall be

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

Which of the following produces coherent waves?