Question

The refracting angle of a prism is ‘A’, and refractive index of
the material of the prism is cot(A/2). The angle of minimum
deviation is : [2015]
(a) 180° – 2A (b) 90° – A
(c) 180° + 2A (d) 180° – 3A

Answer 1

Answer:

180° – 2A

Explanation:

Here, μ=cot(A/2)

Acc. to prism formula,

μ=sin(A+δm2) divided by sin(A/2)

 =cosA/2 divided by sinA/2

sin([A+δm]/ 2)=cosA/2=sn(90∘−A/2)

(A+δm)/2 = 90∘ − A/2  

or δm=(180∘−2A).