NEET 2026 (Phase 1) · PhysicsLoop centre fieldPrevious Year Question
A 100-turn closely wound circular coil of radius 5 cm has a magnetic field of 3.14 × 10⁻³ T at its centre. The current flowing through the coil, and the magnitude of the magnetic moment of this coil are, respectively: (Take μ₀ = 4π × 10⁻⁷ T m/A)
- A.2 A, 10 A m²
- B.2.5 A, 20 A m²
- C.2 A, 4 A m²
- D.2.5 A, 2 A m²✓
Correct Answer
(D) 2.5 A, 2 A m²
Solution & Explanation
Answer: (D) Solution: Field at centre: B = μ₀ N I / (2R). I = 2RB / (μ₀ N) = (2 × 0.05 × 3.14 × 10⁻³) / (4π × 10⁻⁷ × 100) I = (3.14 × 10⁻⁴) / (1.256 × 10⁻⁴) = 2.5 A. Magnetic moment M = N I A = N I (π R²) = 100 × 2.5 × 3.14 × (0.05)² M = 250 × 3.14 × 2.5 × 10⁻³ ≈ 2 A m².
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