Question:

If the refractive index of the material of a prism is \(cot\bigg(\frac{A}{2}\bigg)\), where A is the angle of the prism, then the angle of minimum deviation will be:

Updated On: Nov 13, 2024
  • \(π-3A\)
  • \(π-2A\)
  • \(A\)
  • \(\frac{A}{2}\)
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The Correct Option is B

Solution and Explanation

To find the angle of minimum deviation \( \delta_{\text{min}} \):

Step 1. Given Relation:  
  \( \cot \frac{A}{2} = \frac{\sin \frac{A + \delta_{\text{min}}}{2}}{\sin \frac{A}{2}} \)

Step 2. Rearrange and Simplify: Take the cosine of both sides:  
  \( \cos \frac{A}{2} = \sin \frac{A + \delta_{\text{min}}}{2} \)

Step 3. Solve for \( \delta_{\text{min}} \): Equate the arguments, giving:  
  \( \frac{A + \delta_{\text{min}}}{2} = \frac{\pi}{2} - \frac{A}{2} \)

  - Solving, we get:  
    \( \delta_{\text{min}} = \pi - 2A \)

Thus, the angle of minimum deviation is \( \pi - 2A \).

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