Given that a light ray enters a glass prism at angle of 50 degrees from the normal and is refracted to an angle of 30 degrees from the normal, calculate the speed of light in glass.

Answer: 1.9610⁸ms^-1.Snell's law tells us that n₁sin(x₁)= n₂ sin(x₂) where x is the angle of a light ray from the normal. Air can be assumed to have a refractive index of 1. Therefore, sin(x₁) = n₂ sin(x₂). This means that the refractive index of glass can be found to be sin(x₁)/sin(x₂). The refractive index of a substance is given as the speed of light in a vacuum divided by the speed of light whilst travelling through the substance. Substituting n₂ to be c/v gives c/v = sin(x₁)/sin(x₂). The speed of light in glass can be found by rearranging this equation so that velocity is the subject of the equation. This gives v= c sin(x₂)/sin(x₁). Putting in the values for the two angles gives that the speed of light in glass is equal to c* sin(30)/sin(50) which is equal to 1.96*10⁸ms^-1.