If a glass prism is dipped in water, its dispersive power

Dispersive power of a prism  $\omega =\frac{{\mu }_V-{\mu }_R}{{\mu }_y-1} (when prism is in air)$

When outside medium is changed to water, new dispersive power is given by
 $\begin{array}{l}{\omega }_{new}=\frac{\frac{{\mu }_V}{{\mu }_w}-\frac{{\mu }_R}{{\mu }_w}}{\frac{{\mu }_y}{{\mu }_w}-1} = \frac{{\mu }_V - {\mu }_R}{{\mu }_y - {\mu }_w }\\ Hence dispersive power increases when prism is dipped in water.\end{array}$