63. A thin prism having refracting angle 10° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of second prism should be ?

63. A thin prism having refracting angle 10° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of second prism should be ?

(a) 6°

(b) 8°

(c) 10°

(d) 4°

Answer :  (a) 6°

\(\delta_{min1} = \delta_{min2}\)

\(A_{1}(\mu_{1} - 1) = A_{2}(\mu_{2} - 1)\)