Shown in the figure is a conductor carrying a current $I$. The magnetic field intensity at the point $O$ (common centre of all the three arcs) is
$\frac{{5{\mu _0}I\theta }}{{24\pi r}}$
$\frac{{{\mu _0}I\theta }}{{24\pi r}}$
$\frac{{1{\mu _0}I\theta }}{{24\pi r}}$
zero
A uniform circular wire loop is connected to the terminals of a battery. The magnetic field induction at the centre due to $A B C$ portion of the wire will be (length of $A B C=l_1$, length of $A D C=l_2$ )
If an electron revolves around a nucleus in a circular orbit of radius $R$ with frequency $n$, then the magnetic field produced at the centre of the nucleus will be
A uniform wire is bent in the form of a circle of radius $R$. A current $I$ enters at $A$ and leaves at $C$ as shown in the figure :If the length $ABC$ is half of the length $ADC,$ the magnetic field at the centre $O$ will be
A coil having $N$ $turns$ is wound tightly in the form of a spiral with inner and outer radii $a$ and $b$ respectively. When a current $I$ passes through the coil, the magnetic field at the centre is
The magnetic field $d\overrightarrow B $ due to a small current element $d\overrightarrow {l\,} $ at a distance $\overrightarrow {r\,} $ and element carrying current $i$ is