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Two beams, A and B whose… (Class 12 Physics 2024, Q11)

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PhysicsCBSE Class 12 · Board exam 2024, set 55/1/1 · 1 mark · MCQ

CBSE Class 12 Physics 2024: question 11

Set in the CBSE Class 12 board exam of 2024, paper 55/1/1, section A, question 11, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q11 · 1 mark · MCQDual Nature of Radiation and Matter

Two beams, A and B whose photon energies are 3.3 eV and 11.3 eV respectively, illuminate a metallic surface (work function 2.3 eV) successively. The ratio of maximum speed of electrons emitted due to beam A to that due to beam B is :

  1. (A)3
  2. (B)9
  3. (C)
  4. (D)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/1/1.

Hints

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

Hint 1

Use Einstein's photoelectric equation for each beam.

Hint 2

Speed varies as the square root of kinetic energy.

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. Maximum kinetic energy is . For beam A: eV. For beam B: eV.

  2. Since , the ratio is . Option (C).

    1 mark

Answer: 1/3, option (C)

Where the marks are

  • Finds K = 1 eV and 9 eV and takes the square root of their ratio to get 1/3 (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 paper2024 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.