First slide
Magnetic field due to a current carrying circular ring
Question

A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is

Moderate
Solution

B=μ0i2r=μ0i2(l2π)=πμ0il Now 2πr'n=l r'=l2πn Therefore, B'=μ0ni2r'=μ0πil n2 =Bn2=B(2)2=4B

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