The diagram given below shows light travelling from air into glass. Four angles A, B, C and D are shown. Which of the following formulae is used to calculate the refractive index μ of the glass?

1. μ = $\dfrac{\text{sin A}}{\text{sin C}}$

2. μ = $\dfrac{\text{sin C}}{\text{sin A}}$

3. μ = $\dfrac{\text{sin B}}{\text{sin C}}$

4. μ = $\dfrac{\text{sin B}}{\text{sin A}}$

μ = $\dfrac{\text{sin B}}{\text{sin C}}$

Reason — The refractive index of second medium with respect to the first medium is defined as the ratio of the sine of the angle of incidence in the first medium to the sine of the angle of refraction in the second medium.

∴ Refractive index of glass with respect to air (μ) = $\dfrac{\text{sin B}}{\text{sin C}}$

where

B = angle of incidence in air

r = angle of refraction in glass