Question

A thin prism p₁ with angle 4° and made from glass of refractive index 1.54 is combined with another prism p₂ made from glass of refractive index 1.92 to produce dispersion without deviation. Then the angle of prism P₂ is 

A. 2.3° B. 4.3° C. 3.2° D. 2.0°

Answer 1

The angle of deviation for a prism the is given by

∆ = (n – 1) × A 

Where, 

n = refractive index of prism 

A = angle of prism 

Given: The two prisms when combined produce dispersion without deviation. 

Conclusion: For no deviation for the two prism the deviation caused by two prism should be opposite to each other 

(n₁ – 1)×A₁ = (n₂ – 1) × A₂ 

A₂ = \(\frac{(n_1\,-\,1)\times\,4}{n_2\,-\,1}\)

A₂ = \(\frac{(1.54-1)\times\,4}{(1.92-1)}\)

A₂ = 2.3°