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

In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between the two coherent sources $d$ is kept constant. If the distance between the slit and the eyepiece $D$ is varied as $D_1, D_2, D_3, D_4$ and the corresponding measured fringe widths are $W_1, W_2, W_3, W_4$,then:

In a Fresnel's biprism experiment,fringes are obtained in the focal plane of an eyepiece at a distance of $1 \ m$ from the slit. $A$ convex lens is placed between the biprism and the eyepiece. The images of the slit are formed at two positions of the lens. The distances between the two images of the slit at these two positions are $4.05 \times 10^{-3} \ m$ and $2.9 \times 10^{-3} \ m$ respectively. Calculate the distance between the slits.

White light reflected from a soap film (Refractive Index $\mu = 1.5$) has a maxima at $600 \ nm$ and a minima at $450 \ nm$ with no minimum in between. Then the thickness of the film in units of $10^{-7} \ m$ is:

In Fresnel's biprism $(\mu = 1.5)$ experiment,the distance between the source and the biprism is $0.3\, m$,the distance between the biprism and the screen is $0.7\, m$,and the angle of the prism is $1^\circ$. The fringe width with light of wavelength $6000\ \mathring{A}$ will be: (in $, cm$)

Some currency notes (to avoid counterfeits) change their colour as you tilt them. This is due to