Question

A thin prism $P_1$ with an angle $6^{\circ}$ and made of glass of refractive index $154$ is combined with another prism $P_2$ made from glass of refractive index $172$ to produce dispersion without average deviation The angle of prism $P_2$ is

• A. $7.8^{\circ}$
• B. $4.5^{\circ}$
• C. $6^{\circ}$
• D. $1.3^{\circ}$

Answer 1

Answer: (B)

$4.5^{\circ}$

Answer 2

The correct answer is (B) : $4.5^{\circ}$
δ1​=δ2​ [for no average deviation]
⇒6∘(1.54−1)=A(1.72−1)
⇒A=0.726∘×0.54​
=418∘​=4.5∘