Question

monochromatic light of wavelength λ=800nm illuminates normally a thin liquid film with nf =4/3 and t=500nm lying on a glass of refractive index n=2.5 The liquids refractive index can be continuously increased up to some limiting value by applying a variable voltage across it.

a) If the applied voltage increases nf from (4/3) to(3.0),how many times and for what values of nf does the surface of the film become very bright during this process?

b) If the refractive index is kept constant at nf =2.0 ,calculate the intensity of reflected light in terms of intensity I0 of the incident light.