Question

White light is passed through a prism of angle $5^{\circ }$. If the refractive indices for red and violet colours are 1.641 and 1.659 respectively, the angle of dispersion between them is

• A. ${0.090}^{\circ }$
• B. ${3.295}^{\circ }$
• C. ${3.205}^{\circ }$
• D. $\text{None of these}$

Answer 1

The correct option is A ${0.090}^{\circ }$


Angle of dispersion $\theta ={\delta }_V-{\delta }_R$
For a small angle prism of angle $A$, angle of deviation $\delta =(\mu -1)A$
$\therefore \theta =({\mu }_V-1)A-({\mu }_R-1)A=({\mu }_V-{\mu }_R)A$
$=(1.659-1.641)5^{\circ }={0.090}^{\circ }$