First slide

Coherent sources and their importance in interference

Question

A thin convex lens of refractive index 1.5 is coated with a thin film of refractive index 1.2 in order to reduce the reflection from its surface at $λ = 480 n m$ . Find the maximum thickness of the film which will minimize the intensity of the reflected light.

Moderate

A

$10^{- 7} m$
B

$10^{- 6} m$
C

$2 \times 10^{- 7} m$
D

$3 \times 10^{- 6} m$

Solution

$H e r e, p a t h d i f f e r e n c e i s Δ x = 2 μ t = \frac{λ}{2} \Rightarrow t = \frac{λ}{4 μ} = \frac{480 \times 10^{- 9}}{4 \times 1.2} = 10^{- 7} m$

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