Q.1. A glass prism deviates the red and violet rays through 9∘ and 11∘ respectively. A second prism of equal angle deviates them through 11∘ and 13∘ respectively. The ratio of dispersive power of second prism to first prism is
A. 5 : 6
B. 6 : 5
C. 9 : 13
D. 13 : 9
Answer :- A. 5 : 6
Explanation :-
Dispersive Power of Prism:
\omega = \frac{\delta_v - \delta_r}{\delta_y} \delta_y = \frac{\delta_v + \delta_r}{2} = \frac{11 + 9}{2} \therefore \, \text{For first Prism,} \omega_1 = \frac{2(11 - 9)}{11 + 9} = \frac{1}{5} \text{For Second Prism:} \omega_2 = \frac{2(13 - 11)}{13 + 11} = \frac{1}{6}Ratio :
\frac{\omega_2}{\omega_1} = \frac{\frac{1}{6}}{\frac{1}{5}} = \frac{5}{6}Therefore, the ratio is 5:6