Q. A prism of certain angles deviates the red and blue rays by $8{^\circ}$ and $12{^\circ}$ respectively. Another prism of the same angle deviates the red and blue rays by $10{^\circ}$ respectively. The prisms are small angled and made of different materials. The dispersive powers of the materials of the prism are in the ratio
A) 5 : 6
B) 9 : 11
C) 6 : 5
D) 11 : 9
Explanation
(c) Dispersive power, $\omega = \frac{\delta_{B} - \ \delta_{R}}{\delta}$
$for\ 1st\ prism,\ \omega_{1} = \frac{\delta_{B} - \delta_{R}}{\delta} = \frac{12{^\circ} - 8{^\circ}}{10{^\circ}} = \frac{2}{5}$
Where $\delta = \ \frac{\delta_{B} + \ \delta_{R}}{2}$
Similarly for second prism,
$\omega_{2} = \frac{14{^\circ} - 10{^\circ}}{12} = \frac{1}{3}$
$\therefore\frac{\omega_{1}}{\omega_{2}} = \frac{2}{5} \times \frac{3}{1} = \frac{6}{5}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.