YG File

High quality lenses are often coated to prevent reflection. A lens has an optical index of refraction of 1.72 and a coating with an optical index of recraction 1.31. For near normal incidence the minimum thickness of the coating to prevent reflection for wavelength of 530 nm is
1. 3/4
2. 1/5
3.1/10
4.7/4
(all in mu m ie 10^-6)

Please explain .....