 AP Free Response Question 2000 B4
A sheet of glass has an index of refraction ng = 1.50. Assume that the index of refraction for air is na = 1.00.

 (a) Monochromatic light is incident on the glass sheet, as shown in the figure below, at an angle of incidence of 60º. On the figure, sketch the path the light takes the first time it strikes each of the two parallel surfaces. Calculate and label the size of each angle (in degrees) on the figure, including angles of incidence, reflection, and refraction at each of the two parallel surfaces shown. (b) Next a thin film of material is to be tested on the glass sheet for use in making reflective coatings. The film has an index of refraction nf = 1.38. White light is incident normal to the surface of the film as shown below. It is observed that at a point where the light is incident on the film, light reflected from the surface appears green ( = 525 nm). i. What is the frequency of the green light in air?

 ii. What is the frequency of the green light in the film?

 iii. What is the wavelength of the green light in the film?

 iv. Calculate the minimum thickness of film that would produce this green reflection.