A plastic film with index of refraction 1.80 is put on the surface of a car window to increase the reflectivity and thereby to keep the interior of the car cooler. The widow glass gas index of refraction 1.60.
What minimum thickness is required, if light of wavelength 600 nm in air reflected from the two sides of the film is to interfere constructively?
(b) It is found to be difficult to manufacture and install coatings as thin as calculated in part (a). What is the next greatest thickness for which there will also be constructive interference?

Answer

`[(a) 8.33 xx 10^(-8)m; (b) 2.5 xx 10^(-7)]`