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Question 20267
JEE Physics · Hard

Principles of Communication: Optical Fibre MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Optical FibreHardQuestion 20267

Question

The numerical aperture (NA) of an optical fibre is related to core and cladding refractive indices n₁ and n₂ by:
  1. A
    NA = n₁ − n₂
  2. B
    NA = √(n₁² − n₂²)
    Correct
  3. C
    NA = n₁ / n₂
  4. D
    NA = (n₁ + n₂) / 2

Correct answer

NA = √(n₁² − n₂²)

Explanation

NA = √(n₁² − n₂²) = n₁ sin θmax, where θmax is the half-angle of the acceptance cone. Higher NA → larger acceptance cone → easier coupling but more modal dispersion. Typical single-mode fibre NA ≈ 0.1–0.15.

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