Question

A light wave travelling linearly in a medium of dielectric constant 4, incident on the horizontal surface separating medium with air. The angle of incidence for which the total intensity of the incident wave will be reflected back into the same medium will be:

[Given relative permeability of the medium (µ_r = 1)]

Options

• 10°

• 20°

• 30°

• 60°

Answer 1

60°

Explanation:

Refractive index of the medium

n = `sqrt(μ_r xx ∈_r)`

= `sqrt(1 xx 4)`

= 2

Now, `θ_c = sin^-1(1/n)`

= `sin^-1 (1/2)`

= 30°

If ∠i > ∠θ_c TIR takes place

⇒ ∠i = 60° (According to the given options)