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

Refractive index of a medium (n_m) = $\dfrac{\text{Speed of light in vacuum}}{\text{Speed of light in the medium}}$

Speed of light in vacuum (c) = 3 x 10⁸ ms^-1

Refractive index of glass (n_g) = 1.50

Substituting the values we get,

$1.5 = \dfrac{3 \times 10^8}{\text{Speed of light in glass}} \\ [0.5em] \Rightarrow \text{Speed of light in glass} = \dfrac{3 \times 10^8}{1.5} \\ [0.5em] \Rightarrow \text{Speed of light in glass} = 2 \times 10^8$

Hence, Speed of light in glass = 2 x 10⁸ ms^-1