Question

The velocity of light in a medium is 1.5 × 10⁸ ms⁻¹. The critical angle C for a ray going from the medium into air is ______.

Options

• 30°

• 45°

• 60°

• 90°

Answer 1

The velocity of light in a medium is 1.5 × 10⁸ ms⁻¹. The critical angle C for a ray going from the medium into air is 30°.

Explanation:

Given: Velocity of light in medium, v = 1.5 × 10⁸ m/s

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

The refractive index (n) of the medium relative to air is:

n = `c/v`

= `(3 xx 10^8)/(1.5 xx 10^8)`

= 2

The critical angle (C) is given by:

sin C = `1/n`

= `1/2`

= 0.5

C = sin⁻¹ (0.5)

= 30°