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How would the stopping… (Class 12 Physics 2023, Q20b)

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PhysicsCBSE Class 12 · Board exam 2023, set 55/5/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2023: question 20(b)

Set in the CBSE Class 12 board exam of 2023, paper 55/5/1, section B, question 20(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q20(b) · 2 marks · Very short answerDual Nature of Radiation and Matter

How would the stopping potential for a given photosensitive surface change if (i) the frequency of the incident radiation were increased ? and (ii) the intensity of incident radiation were decreased ? Justify your answer.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 55/5/1.

Hints

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

Hint 1

Write Einstein's photoelectric equation in terms of the stopping potential.

Hint 2

Intensity changes the number of photons. Does it change the energy of each photon?

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. (i) The stopping potential increases when the frequency is increased.

    ½ mark

  2. Justification: Einstein's equation gives , so . Hence increases linearly with .

    ½ mark

  3. (ii) The stopping potential remains the same when the intensity is decreased.

    ½ mark

  4. Justification: The intensity only changes the number of photons, and hence the number of photoelectrons. The energy of each photon () does not change. So the maximum kinetic energy of the photoelectrons, and therefore , is independent of intensity.

    ½ mark

Answer: (i) Stopping potential increases; (ii) stopping potential remains unchanged

Where the marks are

  • Stopping potential increases with frequency (½ mark)
  • Justification using (½ mark)
  • Stopping potential unchanged with intensity (½ mark)
  • Justification: photoelectron energy is independent of intensity (½ 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 55/5/1: 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.