1. 6.28 × 10⁻⁴ T 2. 6.28 × 10⁻² T 3. 12.56 × 10⁻² T 4. 12.56 × 10⁻⁴ T

Answer: 3. 12.56 × 10⁻² T Field at the centre of a long solenoid is B=μ₀ nI . n=100 turns/mm =10⁵ turns/m. B=4π×10⁻⁷×10⁵×1=0.1256\ T=12.56×10⁻²\ T Option (3). The radius is not needed.

Topic: Ampere's law: straight wire and solenoid· Magnetic Effects of Current and Magnetism

A long solenoid of radius 1 mm has 100 turns per mm. If 1 A current flows in the solenoid, the magnetic field strength at the centre of the solenoid is :

1. \(6.28 \times 10^{-4}\) T

2. \(6.28 \times 10^{-2}\) T

3. \(12.56 \times 10^{-2}\) T

4. \(12.56 \times 10^{-4}\) T

Doubtly Asked 30 Oct 2026 NEET UG 2022 Practice test neet Save WhatsApp Report

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Answer: 3. \(12.56 \times 10^{-2}\) T

Field at the centre of a long solenoid is \(B=\mu_0 nI\).

\(n=100\) turns/mm \(=10^{5}\) turns/m.

\(B=4\pi\times10^{-7}\times10^{5}\times1=0.1256\ \text{T}=12.56\times10^{-2}\ \text{T}\)

Option (3). The radius is not needed.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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A long solenoid of radius 1 mm has 100 turns per mm. If 1 A current flows in the solenoid, the magnetic field strength at the centre of the solenoid is :

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