$(i)$ What is meant by dispersion of white light? Draw a diagram to show the dispersion of white light by a glass prism.
$(ii)$ Light of two colours $A$ and $B$ pass through a prism. $A$ deviates more than $B$ from its path of incidence. Which colour has a higher speed in the prism?

(B) $(i)$ The phenomenon of splitting of white light into its constituent colours (spectrum) when passing through a glass prism is called dispersion of light.
$(ii)$ The deviation of light depends on its refractive index in the medium. $A$ higher deviation implies a higher refractive index,and since refractive index is inversely proportional to the speed of light in that medium $(n = c/v)$,the colour that deviates more $(A)$ travels slower. Therefore,the colour that deviates less $(B)$ has a higher speed in the prism.