Q134 / 180 · AIIMS 2015 · Physics

Assertion : In optical fibre, the diameter of the core is kept small. Reason : The smaller diameter of the core ensures that the fibres should have incident angle more than the critical angle required for total internal reflection.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
  • Correct answer
    C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

Diameter of a single mode optical fibre lies between 8 to $10.5 \mu \mathrm{m}$ Critical angle for total internal reflection does not depend on width of media.

Hence, the correct answer is option: 'C'.

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