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Assertion (A) : Photoelectric… (Class 12 Physics 2026, Q16)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 1 mark · Assertion-reason

CBSE Class 12 Physics 2026: question 16

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, 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-basedDual Nature of Radiation and Matter

Assertion (A) : Photoelectric effect is a spontaneous phenomenon.
Reason (R) : According to the wave picture of radiation, an electron would take hours/days to absorb sufficient energy to overcome the work function and come out from a metal surface.

  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)Both Assertion (A) and Reason (R) are false.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

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

Hint 1

Is there any time lag in photoemission?

Hint 2

Does the wave picture explain the instant emission, or contradict it?

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. Photoemission begins immediately (within about s), so A is taken as true.

  2. R correctly states the wave-theory prediction of a long delay. That prediction contradicts what is observed, so it does not explain A. Hence both are true but R is not the correct explanation.

    1 mark

Answer: Option (B)

Where the marks are

  • Both true, R not the explanation (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 paper2026 board paper, set 55/5/1: 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.