Discuss the below:
Q: A layer of oil of thickness 200nm floats on top of a layer of water of thickness 400nm resting on a flat metallic mirror. The index of refraction of oil is 1.24 and that of the water is 1.33. A beam of light is normally incident on these layers. What must be the wavelength of the beam if the light reflected by the top surface of oil is to interfere destructively with the light reflected by the mirror?