Question

Compare the dispersive powers of two prisms if one of them deviates the blue and red rays through $10^{\circ}$ and $6^{\circ}$ respectively and the second prism through $8^{\circ}$ and $4.5^{\circ}$

• A. $0.69$
• B. $0.79$
• C. $0.89$
• D. $0.99$

Answer 1

Answer: (C)

Dispersive power $=\frac{\delta_{v}-\delta_{r}}{\delta_{y}}$
$\delta_{y}=\frac{\delta_{v}+\delta_{r}}{2}$
$w_{1}=\frac{10-6}{8}=\frac{1}{2}$
$w_{2}=\frac{8-4.5}{6.25}=\frac{3.5}{6.25}$
$\frac{w_{1}}{w_{2}} \approx 0.89$