A soap film (n = 1.33) is 290 nm thick and lies on a glass plate (n = 1.52). Sunlight, whose wavelengths (in vacuum) extend from 380 to 750 nm, travels through air and strikes the film perpendicularly. What is the vacuum wavelength ? vacuum in the visible range (380 nm to 750 nm) at which destructive interference causes the film to look dark in reflected light?