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Assertion (A) : A charged… (Class 12 Physics 2025, Q13)

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PhysicsCBSE Class 12 · Board exam 2025, set 55/7/1 · 1 mark · Assertion-reason

CBSE Class 12 Physics 2025: question 13

Set in the CBSE Class 12 board exam of 2025, paper 55/7/1, section A, question 13, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q13 · 1 mark · Assertion-reasonCompetency-basedMoving Charges and Magnetism

Assertion (A) : A charged particle is moving with velocity in x-y plane, making an angle with x-axis. If a uniform magnetic field is applied in the region, along y-axis, the particle will move in a helical path with its axis parallel to x-axis.
Reason (R) : The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.

  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 2025 board paper, set 55/7/1.

Hints

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

Hint 1

Split into components parallel and perpendicular to .

Hint 2

Which direction does point in?

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 velocity component along y is parallel to and stays unchanged, while the x component makes the particle circle. So the helix axis is along y, not x, and A is false.

    ½ mark

  2. The magnetic force is perpendicular to , not along it, so R is false.

    ½ mark

Answer: Option (D)

Where the marks are

  • Shows the helix axis is along (y) and that the force is perpendicular to (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Moving Charges and Magnetism, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 55/7/1: 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.