Question

6.)The refractive index of glass and water with respect to air are 3/2 and 4/3 respectively. if the speed of light in glass is 2×10 8^ m/s, find the speed of light in air
.

Answer 1

Answer :-

3 × 10⁸ ms⁻¹

Explanation :-

Let, speed of light in air be v

Given that refractive index of glass with respect to air is 3/2

also given that, speed of light in glass is 2 × 10⁸ ms⁻¹

▶The refractive index of medium 2 with respect to medium 1 is given by the ratio of speed of light in medium 1 and the speed of light in medium 2 .

This is represented as

▸R.I. of medium 2 with respect to medium 1 = n₂₁ = speed of light in medium 1 / speed of light in medium 2

so,

→ 3 / 2 = v / (2 × 10⁸)

→ v = 3 ( 2 × 10⁸ ) / 2

→ v = ( 6 × 10⁸ ) / 2

→ v = 3 × 10⁸ ms⁻¹

Therefore,

Speed of light in air is 3 × 10⁸ ms⁻¹.

• The ratio of the speed of any medium with the speed of air is known as the absolute refractive index of that medium. ( Or the refractive index of any medium with respect to air is called absolute R.I. of that medium )