A given length of wire forms a single-turn circular coil producing magnetic field B at its centre. If the same wire is reshaped into a two-turn circular coil carrying the same current, find the field at the new centre.
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Question

A given length of wire forms a single-turn circular coil producing magnetic field B at its centre. If the same wire is reshaped into a two-turn circular coil carrying the same current, find the field at the new centre.

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G1 Physics · Accepted Answer

Step 1: Original wire length fixes total circumference n(2πr) when wound into n equal circular turns. Step 2: Doubling number of turns halves turn radius; field B(n)=μ₀nI/(2r). Step 3: B(n) ∝ n², so doubling turns multiplies field by 4. Answer C (4B). Final answer: (C) 4B.