A thin prism P1 with angle 4o and made from glass of refractive index 1.54 is combined with another thin prism…

Q: A thin prism P1 with angle 4o and made from glass of refractive index 1.54 is combined with another thin prism P2 made from glass of refractive index 1.72 to produce dispersion without deviation. The angle of the prism P2 is

(A) 5.33o

(B) 4o

(C) 3o

(D) 2.6o

Ans: (C)

Sol: As net deviation = 0

$\large (\mu_1 – 1)A_1 – (\mu_2 – 1)A_2 = 0 $

$\large (\mu_1 – 1)A_1 = (\mu_2 – 1)A_2 $

$\large A_2 = \frac{(\mu_1 – 1)A_1}{\mu_2 – 1} $

$\large A_2 = \frac{(1.54 – 1)4}{1.72 – 1} = 3^o$