White light is reflected from a thin film suspended in air (e.g. a soap film) with an angle of incidence, as measured in the air, of 0. If the refractive index of the film relative to air is n, and its thickness is d, show that the condition for destructive (a) interference is: mà = 2d (n? - sin² 0)

White light is reflected from a thin film suspended in air (e.g. a soap film) with an angle of incidence, as measured in the air, of 0. If the refractive index of the film relative to air is n, and its thickness is d, show that the condition for destructive (a) interference is: mà = 2d (n? - sin² 0)