WAEC Physics 2015 Paper

Concept:The speed of light in a medium depends on the refractive index for that colour.Explanation:In glass, different colours have different refractive indices.The speed of light in a medium is given by $v = \frac{c}{n}$.Here, $c$ is the speed of light in vacuum and $n$ is the refractive index of the medium for that colour.Blue light is refracted more than red light in glass.This means the refractive index of blue light is greater than that of red light.Since speed is inversely proportional to refractive index, higher $n$ gives lower speed.Therefore, red light travels faster than blue light through the glass prism.Answer:B. refractive index of blue light is greater than that of red light