White light, with a uniform intensity, is perpendicularly incident on a water film of refractive index 1.33 and thickness 320 nm , that is suspended in air. At what wavelength is the light reflected by the film brightest to an observer?

Question

White light, with a uniform intensity, is perpendicularly incident on a water film of refractive index 1.33 and thickness 320 nm , that is suspended in air. At what wavelength is the light reflected by the film brightest to an observer? (A) 459 nm (B) 567 nm (C) 623 nm (D) 690 nm

Tardigrade Admin · Accepted Answer

The film appears bright due to interference of reflected rays The film will appear bright, when 2μ t cos r=(2n+1)(λ/2) ⇒ 2×1.33×320 nm cos 0°=(2×1+1)(λ/2) ⇒ λ=567 nm

Q. White light, with a uniform intensity, is perpendicularly incident on a water film of refractive index $1.33$ and thickness $320 nm$ , that is suspended in air. At what wavelength is the light reflected by the film brightest to an observer?

459 nm

567 nm

623 nm

690 nm

The film appears bright due to interference of reflected rays
The film will appear bright, when
$2 μ t cos r = (2 n + 1) \frac{λ}{2}$
$\Rightarrow 2 \times 1.33 \times 320 nm cos 0^{\circ} = (2 \times 1 + 1) \frac{λ}{2}$
$\Rightarrow λ = 567 nm$

Q. White light, with a uniform intensity, is perpendicularly incident on a water film of refractive index 1.33 and thickness 320nm , that is suspended in air. At what wavelength is the light reflected by the film brightest to an observer?