A current $I$ flows in an infinitely long wire with cross-section in the form of a semicircular ring of radius $R$. The magnitude of the magnetic induction along its axis is
$\frac{{{\mu _0}I}}{{{\pi ^2}R}}$
$\frac{{{\mu _0}I}}{{{2\pi ^2}R}}$
$\frac{{{\mu _0}I}}{{2{\pi}R}}$
$\frac{{{\mu _0}I}}{{{4\pi}R}}$
When a certain length of wire is turned into one circular loop, the magnetic induction at the centre of coil due to some current flowing is ${B_1}$ If the same wire is turned into three loops to make a circular coil, the magnetic induction at the center of this coil for the same current will be
In the figure, shown the magnetic induction at the centre of there $arc$ due to the current in portion $AB$ will be
A straight wire of diameter $0.5\, mm$ carrying a current of $1\, A$ is replaced by another wire of $1\, mm$ diameter carrying the same current. The strength of magnetic field far away is
Due to $10\, ampere$ of current flowing in a circular coil of $10\, cm$ radius, the magnetic field produced at its centre is $3.14 \times {10^{ - 3}}\,Weber/{m^2}$. The number of turns in the coil will be
A straight wire of finite length carrying current $l$ subtends an angle of $60^{\circ}$ at point $P$ as shown. The magnetic field at $P$ is