A thin prism P 1 with an angle 6 ° and made of glass of refractive index 1 . 54 is combined with another prism P 2 made from glass of refractive index 1 . 72 to produce dispersion without average deviation. The angle of prism P 2 is :

Step-by-step solution

For no average deviation, δ 1 + δ 2 = 0 ⇒ A μ 1 - 1 - B μ 2 - 1 = 0 ⇒   6 °   ( 1 . 54   –   1 )   =   θ ( 1 . 72   –   1 ) ⇒ θ = 6 ° × 0 . 54 0 . 72 = 4 . 5 °