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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 :
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- 180° – 2A
- 90° – A
- 180° + 2A
- 180° – 3A
Correct Option: A
As we know, the refractive index of the material of the prism
| μ = | sin |  |  | |||
| 2 | ||||||
| sin (A / 2) | ||||||
| cot (A / 2) = | sin | | | = | |||
| 2 | |||||||
| sin (A / 2) | sin (A / 2) | ||||||
[∵ μ = cot (A / 2) ]
| ⇒ sin | | | = sin(90° + A / 2) | |
| 2 |
⇒ δmin = 180° - 2A
