Question

A thin layer of air is between 2 pieces of glass. When white light is incident upon them, green light of 520 nm is reflected back strongly, but blue light of 433.33 nm appears dark. What is a possible thickness of the air layer?

Answer 1

t = thickness

$\lambda$_green = 520

$\lambda$_blue = 433.33

for reflected back strongly ,:

2t = n $\lambda$_green                               eq-1

for darkness :

2t = (n + 0.5) $\lambda$_blue                               eq-2

using eq-1 and eq-2

n $\lambda$_green = (n + 0.5) $\lambda$_blue

n (520) = (n + 0.5) (433.33)

n = 2

using eq-1

2t = n $\lambda$_green   

2 t = 2 (520)

t = 520 nm