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Assertion (A)… (Class 12 Physics SQP 2023-24, Q16)

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PhysicsCBSE Class 12 · Sample paper, session 2023-24 · 1 mark · Assertion-reason

CBSE Class 12 Physics sample paper 2023-24: question 16

From the official CBSE sample question paper for 2023-24, section A, question 16, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q16 · 1 mark · Assertion-reasonCompetency-basedRay Optics and Optical Instruments

Assertion (A): Propagation of light through an optical fibre is due to total internal reflection taking place at the core-cladding interface.
Reason (R): Refractive index of the material of the cladding of the optical fibre is greater than that of the core.

  1. (A)If both Assertion and Reason are true and Reason is correct explanation of Assertion.
  2. (B)If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  3. (C)If Assertion is true but Reason is false.
  4. (D)If both Assertion and Reason are false.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

Open one hint at a time and try again before the next.

Hint 1

State the conditions for total internal reflection.

Hint 2

Light must travel from optically denser to rarer medium.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Light is guided by total internal reflection at the core–cladding interface: A true.

    ½ mark

  2. TIR needs light going from denser to rarer medium, so the cladding has a lower refractive index than the core: R false.

    ½ mark

Answer: Option (C)

Where the marks are

  • A true, R false since cladding index is lower (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Ray Optics and Optical Instruments, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2023-24: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.