40 What is the minimum thickness of a soap film that gives constructive interference for light that has wavelength of 600 nm in soap? 41 A camera lens has an antireflective coating that appears violet when viewed in white light. If the wavelength ofviolet light in the coating is 380 nm. what is the minimum thickness of the coating? 42 Coloured interference fringes are viewed when white light is incident on oil floating on water. The refractive index of oil is 1.5 and the refractive index of water is 1.3. (a) Will there be a phase change on reflection at the oil/ water boundary? (b) Yellow light has wavelength 580 nm in air. What is its wavelength in oil? (c) What is the thinnest thickness of oil that will give constructive interference for vellow light