A circular coil carrying a certain current produces a magnetic field `B_(0)` at its centre.The coil is now rewound so as to have 3 turns and the same current is psses through it.The new magnetic field at the centre is

Options

A. `(B_(0))/(9)`
B. `9 B_(0)`
C. `(B_(0))/(3)`
D. `3B_(0)`

Answer

B

Explanation

`B_(0) = (muNI)/(2a) = (muI xx I)/(2a) = (mu_(0)I)/(2a)` for 1 turn. For rewinding the coil in three turns, new radius `a/3`, number of turns (N') = 3.
`therefore` New magnetic field = `(mu_(0)I xx 3)/(2 xx (a/3)) = (9mu_(0)I)/(2a) = 9B_(0)`