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Assertion (A) : Photoelectric… (Class 12 Physics 2023, Q18)

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

CBSE Class 12 Physics 2023: question 18

Set in the CBSE Class 12 board exam of 2023, paper 55/1/1, section A, question 18, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q18 · 1 mark · Assertion-reasonCompetency-basedDual Nature of Radiation and Matter

Assertion (A) : Photoelectric effect demonstrates the particle nature of light.

Reason (R) : Photoelectric current is proportional to intensity of incident radiation for frequencies more than the threshold frequency.

  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

Check each statement separately.

Hint 2

Which observations actually prove that light behaves as photons?

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. The photoelectric effect is explained only by photons (quanta of ), so the assertion is true. Photocurrent is proportional to intensity above threshold, so the reason is also true.

    ½ mark

  2. However, the particle nature is shown by the threshold frequency and instantaneous emission, not by the proportionality of current to intensity. So R does not explain A: option (B).

    ½ mark

Answer: Option (B)

Where the marks are

  • Both statements true, but R is not the explanation of A (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Dual Nature of Radiation and Matter, 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.