Antireflection coatings can be used on the inner surfaces of eyeglasses to reduce the reflection of stray light into the eye, thus reducing eyestrain. You may want to review (Page) . Part A A 90-nm-thick coating is applied to the lens. What must be the coating's index of refraction to be most effective at 480 nm? Assume that the coating’s index of refraction is less than that of the lens. Express your answer using two significant figures.

1.33

Explanation:

Using the formula for destructive interference since the two reflected ray light waves from eyeglass should be made to cancel each other ( destructive interference) and also refractive index of air less than the refractive index of the film and both are less than the refractive index of the glass meaning the both reflected rays from the air and film will experience a phase change

n film =  ( m + 0.5) ( λ / 2t)

since 2 t = ( m + 0.5) ( λ / n film)

where m is an integer, λ is wavelength, and t is thickness  and n film is the refractive index of film

for effectiveness m = 0

n film = ( 0.5) ( 480 ÷ (2 × 90 ) ) = 1.33