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Assertion (A): Two… (Class 12 Physics SQP 2025-26, Q15)

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PhysicsCBSE Class 12 · Sample paper, session 2025-26 · 1 mark · Assertion-reason

CBSE Class 12 Physics sample paper 2025-26: question 15

From the official CBSE sample question paper for 2025-26, section A, question 15, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q15 · 1 mark · Assertion-reasonCompetency-basedWave Optics

Assertion (A): Two light sources emitting waves of similar wavelengths are coherent.
Reason (R): Two light sources emitting waves having zero or constant phase difference are known as coherent sources.

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

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

What condition defines coherence?

Hint 2

Is equal wavelength enough on its own?

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. Similar wavelengths alone do not make two sources coherent, because their phase difference must also stay constant. The assertion is false.

  2. The scheme marks both statements false and gives option (D).

    1 mark

Answer: Option (D)

Where the marks are

  • Recognises that the assertion is false and selects (D) (1 mark)

Revise the chapter

  • Chapter: Wave Optics (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Wave Optics, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2025-26: 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.