Ray Optics Question 10

Question 10 - 30 January - Shift 2

A thin prism $P_1$ with an angle $6^{\circ}$ and made of glass of refractive index 1.54 is combined with another prism $P_2$ made from glass of refractive index 1.72 to produce dispersion without average deviation. The angle of prism $P_2$ is :

(1) $6^{\circ}$

(2) $1.3^{\circ}$

(3) $7.8^{\circ}$

(4) $4.5^{\circ}$

Show Answer

Answer: (4)

Solution:

Formula: Refraction Through Prism

$\delta_1=\delta_2$ [for no average deviation]

$\Rightarrow 6^{\circ}(1.54-1)=A(1.72-1)$

$\Rightarrow A=\frac{6^{\circ} \times 0.54}{0.72}$

$ =\frac{18^{\circ}}{4}=4.5^{\circ} $