High-quality camera 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 os refraction 1.31. For near normal incidence, the minimum thickness of the coating to prevent reflection for wavelength of `5.3 xx 10^(-7) m` is

Options

A. `0.75 mu m`
B. 0.2 mm
C. `0.1 mu m`
D. 1.75 mm

Answer

c

Explanation

There is no net change in phase produced by the two reflection. Hence,
`(lambda)/(2) = 2 mu_(1) d cos theta`
For normal incidence, `cos theta = 1`.
`:.d = (lambda)/(4 mu_(1)) = (5.3 xx 10^(-7))/(4 xx 1.31) = 10^(-7) m = 0.1 mu m`