PhysicsCBSE Class 12 · Sample paper, session 2026-27 · 3 marks · Short answer

CBSE Class 12 Physics sample paper 2026-27: question 27(B)

From the official CBSE sample question paper for 2026-27, section C, question 27(B), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27(B) · 3 marks · Short answerMoving Charges and Magnetism

I. A small current loop behaves like a tiny magnet when placed in a magnetic field. Using this idea, explain what physical quantity determines the strength and orientation of such a magnetic dipole. Also state the SI unit of this quantity.
II. A steel wire of length $l$ has a magnetic moment $m$ . It is bent into a semicircular arc. What is its new magnetic moment?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Which vector quantity of a loop involves both current and area?

Hint 2

Bending does not change pole strength; only the distance between the ends changes.

Hint 3

Use arc length l = πr to find the new straight-line separation.

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.

I. The magnetic dipole moment $m = N I A$ determines both the strength (magnitude $N I A$ ) and orientation (along the area vector, given by the right-hand rule) of the loop's dipole.
½ mark
SI unit: A m $^{2}$ (equivalently J T $^{- 1}$ ).
½ mark
II. Pole strength of the straight wire: $q_{m} = \frac{m}{l}$ ; it stays the same on bending.
½ mark
On bending into a semicircle of radius r, the poles lie at the ends of a diameter, so the new separation is $2 r$ .
½ mark
Length of arc: $l = π r \Rightarrow r = \frac{l}{π}$ .
½ mark
New moment: $m^{'} = q_{m} \times 2 r = \frac{m}{l} \times \frac{2 l}{π} = \frac{2 m}{π}$ .
½ mark

Answer: I. Magnetic dipole moment, unit A m² (J/T); II. m′ = 2m/π

Where the marks are

Identifies magnetic dipole moment m = NIA (½ mark)
SI unit A m² or J/T (½ mark)
Pole strength m/l (½ mark)
New pole separation 2r (½ mark)
r = l/π (½ mark)
m′ = 2m/π (½ mark)

Revise the chapter

Chapter: Moving Charges and Magnetism (notes, formulas, where marks are lost and every past question)
Topic: Torque on a Current Loop and Magnetic Dipole

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 paperSample paper 2026-27: every question, by section.

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CBSE Class 12 Physics sample paper 2026-27: question 27(B)

Hints

Step-by-step solution

Revise the chapter

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