The refractive index of a particular material is $1.67$ for blue light, $1.65$ for yellow light and 1.63 for red light. The dispersive power of the material is

Given, refractive index for blue light, $\mu_{b}=1.67$ Refractive index for yellow light, $\mu_{y}=1.65$ Refractive index for red light, $\mu_{r}=1.63$ Dispersive power, $\omega=$ ? Dispersive power is the ratio of angular dispersion and mean deviation. The formula of dispersive power is given as $$ \begin{aligned} \omega &=\frac{\mu_{b}-\mu_{r}}{\mu_{y}-1} \\ &=\frac{1.67-1.63}{1.65-1} \\ &=\frac{0.04}{0.65}=0.0615 \end{aligned} $$