When exposed to sunlight,thin films of oil on water often exhibit brilliant colours due to the phenomenon of

Choose the correct statement.

Oil floating on water looks coloured due to interference of light. What should be the order of magnitude of the thickness of the oil layer in order that this effect may be observed? (in $m$)

What is the effect on Fresnel's biprism experiment when white light is used?

The thickness of a plate having refractive index $\mu$ which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it is

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