Question

A silicon monoxide thin film (n = 1.45) of thickness 83.2 nm is applied to a camera lens made of glass (n = 1.55). This will result in destructive interference for reflected light of what wavelength?

483 nm

386 nm

350 nm

603 nm

643 nm

Answer 1

Given

Refractive index of silicon monoxide μ_s = 1.45

Refractive index of glass μ_g = 1.55

Thickness of the film t = 83.2 nm

Solution

Here one light wave is reflected at the surface of the silicon dioxide top

One will go through this and then get get reflected by the glass and go through the refraction once again.

To give us the destructive interference the path difference must be λ/2

2μ_st = λ/2

2 x 1.45 x 83.2 x 10^-9 = λ/2

λ = 482.56 x 10^-9 m

λ = 483 nm