18. Consider a soap lm that is the thinnest lm that will produce a bright blue light when illuminated with the white light. The index of refraction of the soap lm is 1.35 and the blue light is monochromatic with wavelength 41 1 nm. a) Calculate the thickness of the lm if the soap covers a piece of crown glass with index of refraction of 1.52. [2 marks] air on], = 1.00 soap film am," = 1.35 glass amass = 1.52 Suppose the reections oceur instead from the soap lm on water with index of refraction of 1.33. Determine the thickness of the lm on the water that will produce the same blue colour of reected light. [2 marks] 19. Light with wavelength of 540 nm is incident on a diffraction grating that has 8500 lines/cm. Calculate the angles of the maxima. [6 marks]