What is the minimum thickness of a thin film required for constructive interference it the reflected light from it ? Given, the refractive index of the film = 1.5, wavelength of the light incident on the film = 600 nm.

Question

What is the minimum thickness of a thin film required for constructive interference it the reflected light from it ? Given, the refractive index of the film = 1.5, wavelength of the light incident on the film = 600 nm. (A) 50 nm (B) 200 nm (C) 100 nm (D) 300 nm

Tardigrade Admin · Accepted Answer

Condition for constructive interference is 2 μ t=[2 n+1] (λ/2) where, n=0,1,2,3... For minimum thickness, n=0 2 μ t=(λ/2) ⇒ t =(λ/4 μ)=(600 × 10-9/4 × 1.5) = 100 nm

Q. What is the minimum thickness of a thin film required for constructive interference it the reflected light from it ?
Given, the refractive index of the film = $1.5$ , wavelength of the light incident on the film = $600 nm$ .

50 nm

200 nm

100 nm

300 nm

Condition for constructive interference is
$2 μ t = [2 n + 1] \frac{λ}{2}$
where, $n = 0, 1, 2, 3...$
For minimum thickness, $n = 0$
$2 μ t = \frac{λ}{2}$
$\Rightarrow t = \frac{λ}{4 μ} = \frac{600 \times 1 0 ^{- 9}}{4 \times 1.5}$
$= 100 nm$

Q. What is the minimum thickness of a thin film required for constructive interference it the reflected light from it ? Given, the refractive index of the film = 1.5, wavelength of the light incident on the film = 600nm.