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Assertion (A) : The phase… (Class 12 Physics 2023, Q17)

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PhysicsCBSE Class 12 · Board exam 2023, set 55/1/1 · 1 mark · Assertion-reason

CBSE Class 12 Physics 2023: question 17

Set in the CBSE Class 12 board exam of 2023, paper 55/1/1, section A, question 17, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q17 · 1 mark · Assertion-reasonCompetency-basedWave Optics

Assertion (A) : The phase difference between any two points on a wavefront is zero.

Reason (R) : All points on a wavefront are at the same distance from the source and thus oscillate in the same phase.

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

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 55/1/1.

Hints

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

Hint 1

Recall the definition of a wavefront.

Hint 2

Why do these points share the same phase?

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. A wavefront is the locus of points oscillating in the same phase, so the assertion is true.

    ½ mark

  2. For a point source, all points on the wavefront are equidistant from it, which explains the equal phase. Both are true and R explains A, so the answer is option (A).

    ½ mark

Answer: Option (A)

Where the marks are

  • Both statements true and R explains A (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 paper2023 board paper, set 55/1/1: 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.