A length of wire carries a steady current. It is first bent to form a circular coil of one turn. The same length is now bent more sharply to give a double loop of a smaller radius. The magnetic field cause at the centre by the same current is
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Question

A length of wire carries a steady current. It is first bent to form a circular coil of one turn. The same length is now bent more sharply to give a double loop of a smaller radius. The magnetic field cause at the centre by the same current is

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G1 Physics · Accepted Answer

For one turn, L=2πR. For two turns, each loop radius becomes R/2. Since B=μ₀NI/(2r), the new field is μ₀(2)I/[2(R/2)]=4 times the original. Hence C.