Q.

A thin prism P1 with an angle 6° and made of glass of refractive index 1.54 is combined with another prism P2 made from glass of refractive index 1.72 to produce dispersion without average deviation. The angle of prism P2 is               [2023]

1 6°  
2 1.3°  
3 7.8°  
4 4.5°  

Ans.

(4)

δ1=δ2 [for no average deviation]

 6°(1.54-1)=A(1.72-1)

 A=6°×0.540.72=18°4=4.5°