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Draw a graph showing the… (Class 12 Physics 2023, Q19)

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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 19

Set in the CBSE Class 12 board exam of 2023, paper 55/5/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerNuclei

Draw a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Indicate the region in which the nuclear force is (a) attractive and (b) repulsive.

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

Force is related to potential energy by .

Hint 2

The curve has a single minimum at about 0.8 fm. Ask yourself on which side of it the slope gives a force that pulls the nucleons together.

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. Graph (described): Potential energy (MeV) is on the y-axis and separation (fm) is on the x-axis. At very small (below about 0.8 fm) is large and positive and rises steeply as decreases. The curve falls as increases, crosses zero and reaches a minimum (about MeV) at fm. Beyond it rises again and approaches zero for greater than about 2–3 fm, because nuclear force is short-ranged.

    1 mark

  2. (a) Attractive region: for . Here increases with , so the force is negative and pulls the nucleons together. Mark this on the graph to the right of the minimum.

    ½ mark

  3. (b) Repulsive region: for . Here decreases as increases, so is positive and pushes the nucleons apart. Mark this on the graph to the left of the minimum.

    ½ mark

Answer: PE–separation curve with a minimum at fm; attractive for , repulsive for .

Where the marks are

  • Correct shape of the potential energy vs separation graph with a minimum at (1 mark)
  • Attractive region marked (½ mark)
  • Repulsive region marked (½ mark)

Revise the chapter

  • Chapter: Nuclei (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Nuclei, 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.