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The magnetic field at the centre of a circular current loop of radius R carrying current I is:
Aμ₀ I / R²
Bμ₀ I / (4 π R)
Cμ₀ I R / 2
Dμ₀ I / (2 R)
Answer & Solution
Correct answer: D. μ₀ I / (2 R)
1. Integrate Biot-Savart around the loop; symmetry leaves only the axial component.
2. At the centre of a coil of N turns: B = μ₀ N I / (2 R). For N = 1: B = μ₀ I / (2 R).
3. Direction by right-hand rule (curl fingers along I → thumb gives B direction).
_Source: NCERT Class 12 Physics Ch 4 §4.6 Field on the Axis of a Circular Coil_
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