A uniform layer of water (n = 1.33) lies on a glass plate (n = 1.52). Light shines perpendicularly on the layer. Because of constructive interference, the layer looks maximally bright when the wavelength of the light is 403 nm in vacuum and too when it is 605 in vacuum. (a) Get the minimum thickness of the film. (b) Assuming that the film has the minimum thickness and that the visible spectrum extends from 380 to 750 nm, Decide the visible wavelength (in vacuum) for which the film appears totally dark.