A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along +x direction. A magnetic field B = (0.4\ mT)j + (0.6\ mT)k is switched on, in the region. The force acting on the segment is (A) (2j + 3k) mN (B) (-3j + 2k) μN (C) (6j + 4k) mN (D) (-4j + 6k) μN

PhysicsCBSE Class 12 · Board exam 2025, set 55/1/1 · 1 mark · MCQ

CBSE Class 12 Physics 2025: question 3

Set in the CBSE Class 12 board exam of 2025, paper 55/1/1, section A, question 3, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q3 · 1 mark · MCQMoving Charges and Magnetism

A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along +x direction. A magnetic field $B = (0.4 mT) \hat{j} + (0.6 mT) \hat{k}$ is switched on, in the region. The force acting on the segment is

(A) $(2 \hat{j} + 3 \hat{k})$ mN
(B) $(- 3 \hat{j} + 2 \hat{k})$ μN
(C) $(6 \hat{j} + 4 \hat{k})$ mN
(D) $(- 4 \hat{j} + 6 \hat{k})$ μN

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 55/1/1.

Hints

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

Hint 1

Use $F = I l \times B$ .

Hint 2

Remember that $\hat{i} \times \hat{k} = - \hat{j}$ .

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.

$F = I l \times B = 0.5 (0.01 \hat{i}) \times (0.4 \hat{j} + 0.6 \hat{k}) \times 1 0^{- 3}$ N.
½ mark
Using $\hat{i} \times \hat{j} = \hat{k}$ and $\hat{i} \times \hat{k} = - \hat{j}$ : $F = 5 \times 1 0^{- 6} (0.4 \hat{k} - 0.6 \hat{j})$ N $= (- 3 \hat{j} + 2 \hat{k})$ μN. Option (B).
½ mark

Answer: $(- 3 \hat{j} + 2 \hat{k})$ μN, option (B)

Where the marks are

Applies $I l \times B$ with correct cross products and units to get (B) (1 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 paper2025 board paper, set 55/1/1: every question, by section.

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CBSE Class 12 Physics 2025: question 3

Hints

Step-by-step solution

Revise the chapter

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