Question

A prism of a certain angle deviates the red and blue rays by $8$ and $12$ respectively. Another prism of the same angle deviates the red and blue rays by $10$ and $14$ respectively. The prisms are small angled and made of different materials. The dispersive powers of the materials of the prisms are in the ratio

• A. $11:9$
• B. $6:5$
• C. $9:11$
• D. $5:6$

Answer 1

The correct option is B $6:5$

Dispersive power $=\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}=\frac{{\delta }_v+{\delta }_r}{{\delta }_y}$

${\delta }_y=\frac{{\delta }_v+{\delta }_r}{2}$

The ratio of dispersive power is;

$\frac{12-8}{\frac{12+8}{2}}$= $\frac{\frac{4}{10}}{\frac{4}{12}}$ =$\frac{12}{10}$= $6:5$