A thin layer of magnesium fluoride (n = 1.38) is used to coat a flint-glass lens (n = 1.61).

(a) What thickness should the magnesium fluoride film have if the reflection of 565-nm light is to be suppressed? Assume that the light is incident at right angles to the film.

(b) If it is desired to suppress the reflection of light with a higher frequency, should the coating of magnesium fluoride be made thinner or thicker? Explain.