Question

A ray of light is incident on an equilateral glass prism shows minimum deviation is 30°. Calculate the speed of light through prism?

Answer 1

Let $A=60^{\circ}$ be the angle of the prism, $D=30^{\circ}$ be the angle of minimum deviation, then the refractive index $n$ of the material of the prism can be calculated using the formula

$$n=\frac{\sin (A+D)/2}{\sin A/2}=\sqrt{2}.$$

Let $c=300000\, km/h$ be the speed of light in vacuum. The speed $v$ of light through prism can be calculated using the formula

$$v=c/n \approx 212132 \, km/h.$$