A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ $turns$. The magnetic field at the centre of the coil will be
A$nB$
B$n^2B$
C$2nB$
D$2n^2B$
AIEEE 2004,NEET 2016, Easy
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B$n^2B$
b (b) Magnetic field at the center of single turn loop $B = \frac{{{\mu _0}}}{{4\pi }}.\frac{{2\pi i}}{r}$, magnetic field at the center of $n-$turn loop
${B_n} = \left( {\frac{{{\mu _0}}}{{4\pi }}.\frac{{2\pi i}}{{r/n}}} \right) \times n \Rightarrow {B_n} = {n^2}B$
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