3. What is the minimum thickness of an air layer between two flat glass surfaces (a) if the glass is to appear bright when 4.50 X 102-nm light is incident at 90°? (b) if the glass is to appear dark? Use a diagram to explain your reasoning in both cases. 4. A film of gasoline (n = 1.40) floats on water (n = 1.33). Yellow light, of wavelength 5.80 X 102 nm, shines on this film at an angle of 90°. (a) Determine the minimum nonzero thickness of the film, such that the film appears bright yellow from construc- tive interference. (b) What would your answer have been if the gasoline had been spread over glass (n = 1.52) rather than over water? 5. Two plane glass plates 10.0 cm long, touching at one end, are separated at the other end by a strip of paper 1.5 × 10-3 mm thick. When the plates are illuminated by monochromatic light, the average distance between consecutive dark fringes is 0.20 cm. Calculate the wavelength of the light.