What causes change in the colours of the soap or oil films for the given beam of light?

What causes changes in the colours of the soap or oil films for the given beam of light

Explain the colour formation in a thin oil film.

Colours of soap film in sun light is due to

Dark and colour patterns on thin soap films are due to-

What should be the order of the thickness of oil film on the water surface to enable one see the colour in it ?

What is the cause of change in direction of a ray of light on refraction?

A parallel beam of light of wavelength 560 nm falls on a thin film of oil (refractive index = 1.4). What should be the minimum thickness of the film so that it strongly transmit the light ?