Light of wavelength 425.0 nm in air falls at normal incidence on an oil film that is 850.0 nm thick.The oil is floating on a water layer 15 cm thick.The refractive index of water is 1.33,and that of the oil is 1.40.You want to add oil so that light reflected off of the top of the oil film will be canceled.What is the minimum distance that you should INCREASE the oil film?

Question

Quizplus · Accepted Answer

The correct answer is A.The light will be canceled if the reflected waves from the top and bottom of the oil film interfere destructively. This will occur if the path length difference between the two waves is half a wavelength. The path length difference is equal to twice the thickness of the oil film, so the minimum distance that the oil film should be increased is half a wavelength, or 60.7 nm.

Light of Wavelength 425