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 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
A particle carrying a charge equal to $100$ times the charge on an electron is rotating per second in a circular path of radius $0.8$ $metre$. The value of the magnetic field produced at the centre will be $({\mu _0} = $ permeability for vacuum)
A wire $A$, bent in the shape of an arc of a circle, carrying a current of $2\, A$ and having radius $2\, cm$ and another wire $B ,$ also bent in the shape of arc of a circle, carrying a current of $3\, A$ and having radius of $4\, cm ,$ are placed as shown in the figure. The ratio of the magnetic fields due to the wires $A$ and $B$ at the common centre $O$ is
A charge $q$ coulomb moves in a circle at $n$ revolutions per second and the radius of the circle is $r$ metre; then magnetic field at the centre of the circle is
A current loop $ABCD$ is held fixed on the plane of the paper as shown in the figure. The arcs $ BC$ (radius $= b$) and $DA $ (radius $= a$) of the loop are joined by two straight wires $AB $ and $CD$. A steady current $I$ is flowing in the loop. Angle made by $AB$ and $CD$ at the origin $O$ is $30^o $. Another straight thin wire with steady current $I_1$ flowing out of the plane of the paper is kept at the origin.
The magnitude of the magnetic field $(B)$ due to the loop $ABCD$ at the origin $(O)$ is :