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

CBSE Class 12 Physics 2025: question 5

Set in the CBSE Class 12 board exam of 2025, paper 55/1/1, section A, question 5, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q5 · 1 mark · MCQElectromagnetic Induction

You are required to design an air-filled solenoid of inductance 0.016 H having a length 0.81 m and radius 0.02 m. The number of turns in the solenoid should be

(A)2592
(B)2866
(C)2976
(D)3140

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

Write the formula for the self-inductance of a solenoid.

Hint 2

Rearrange it to find $N$ .

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.

For a solenoid, $L = \frac{μ _{0} N ^{2} π r ^{2}}{l}$ , so $N^{2} = \frac{L l}{μ _{0} π r ^{2}}$ .
½ mark
$N^{2} = \frac{0.016 \times 0.81}{4 π \times 1 0 ^{- 7} \times π \times 4 \times 1 0 ^{- 4}} \approx 8.2 \times 1 0^{6}$ , so $N \approx 2866$ . Option (B).
½ mark

Answer: 2866, option (B)

Where the marks are

Uses $L = μ_{0} N^{2} A / l$ and solves for N ≈ 2866 (1 mark)

Revise the chapter

Chapter: Electromagnetic Induction (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Electromagnetic Induction, 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 5

Hints

Step-by-step solution

Revise the chapter

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