Light enters from air to glass, having a refractive index of 1.50. What is the speed of light in the glass? The speed of light in a vacuum is 3 x 108 ms-1.

Refractive index of a medium (nm) = Speed of light in vacuum(C) / Speed of light in the medium(V)

Speed of light in vacuum (c) = 3 × 108 m/s

Refractive index of glass (n_g) = 1.50

Speed of light in the glass (v) = Speed of light in vacuum(C) / Refractive index of glass (n_g)

V = C / n_g

= 3 × 10⁸ / 1.50 = 2 x 10⁸ ms^-1.