Question

Critical angle for total internal reflection from a medium to a vacuum is 60°. Find the velocity of light in the given medium.

Answer 1

Given:

Critical angle, C = 60°

Velocity of light in vacuum, c = 3 × 10⁸ m/s

Step 1: Use the formula for critical angle:

sin C = `1/μ`

μ = `1/(sin C)`

= 1/(sin 60°)

= `1/((sqrt3)/2)`

≈ `1/0.866`

≈ 1.1547

Step 2: Use refractive index to find velocity:

μ = `c/v`

v = `c/μ`

= `(3 xx 10^8)/1.1547`

≈ 2.6 × 10⁸ m/s