Example 1 · level 1
Light travels at 2.4 × 10⁸ m/s in a plastic. Find the absolute refractive index of a plastic (c = 3 × 10⁸ m/s), correct to 2 decimal places.
Show solution
- n = (3 × 10⁸) ÷ (2.4 × 10⁸) = 1.25.
Answer: 1.25
CLASS 10 SCIENCE · LIGHT: REFRACTION
Refractive index and speed of light
Absolute refractive index n = c/v, with c = 3 × 10⁸ m/s. Relative index of medium 2 w.r.t. medium 1: n₂₁ = n₂/n₁ = v₁/v₂.
Loading practice…
Worked examples
Example 2 · level 2
A medium has refractive index 1.5. Find the speed of light in it, in units of 10⁸ m/s (e.g. type 2 for 2 × 10⁸ m/s), correct to 2 decimal places.
Show solution
- v = 3 × 10⁸ ÷ 1.5 = 2 × 10⁸ m/s.
Answer: 2
Example 3 · level 3
Light travels at 2 × 10⁸ m/s in glass and 1.25 × 10⁸ m/s in diamond. Find the refractive index of diamond with respect to glass, correct to 2 decimal places.
Show solution
- n(diamond, glass) = v(glass) ÷ v(diamond) = 2 ÷ 1.25 = 1.6.
Answer: 1.6