A circular coil carrying a certain current produces a magnetic field $B_o$ at its centre. The coil i

Question

A circular coil carrying a certain current produces a magnetic field $B_o$ at its centre. The coil is now rewound so as to have 3 turns and the same current is passed through it. The new magnetic field at the centre is

Professor PC Thomas Classes · Answer

$B = \frac{\mu_0 n I}{2r}$. If rewound to $n=3$, radius becomes $r/3$. $B' = \frac{\mu_0 (3) I}{2(r/3)} = 9 B_0$.