Question

The speed of light in vacuum and in two different glasses is given in the table below:  

Medium	Speed of light
Vacuum	3.00 × 108 m/s
Flint glass	1.86 × 108 m/s
Crown glass	1.97 × 108 m/s

(a) Calculate the absolute refractive indexes of flint glass and crown glass.
(b) Calculate the relative refractive index for light going from crown glass to flint glass.

Answer 1

(a) Absolute refractive index of flint glass = Speed of light in vacuum / Speed of light in flint glass
= (3.00 × 10⁸) / (1.86 × 10⁸)
= 1.61
Absolute refractive index of crown glass = Speed of light in vacuum / Speed of light in crown glass
= (3.00 × 10⁸) / (1.97 × 10⁸)
= 1.52 

(b) Relative refractive index for light going from crown glass to flint glass is given by:
(Speed of light in crown glass) / (Speed of light in flint glass)
= (1.97 × 10⁸) / (1.86 × 10⁸)
= 1.059