A thin ring of $10\, cm$ radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of $40\,\pi \,rad\,{s^{ - 1}}$ about its axis, perpendicular to its plane. If the magnetic field at its centre is $3.8 \times {10^{ - 9}}\,T$, then the charge carried by the ring is close to $\left( {{\mu _0} = 4\pi \times {{10}^{ - 7}}\,N/{A^2}} \right)$
$2 \times {10^{ - 6}}\,C$
$7 \times {10^{ - 6}}\,C$
$4 \times {10^{ - 5}}\,C$
$3 \times {10^{ - 5}}\,C$
Two long straight wires are placed along $x$-axis and $y$-axis. They carry current $I_1$ and $I_2$ respectively. The equation of locus of zero magnetic induction in the magnetic field produced by them is
Which is a vector quantity
A wire carrying current $I$ has the shape as shown in adjoining figure.Linear parts of the wire are very long and parallel to $X-$axis while semicircular portion of radius $R$ is lying in $Y-Z$ plane. Magnetic field at point $O$ is
A plastic disc of radius $R$ has a charge $q$ uniformly distributed over its surface. If the disc is rotated at an angular frequency $\omega$ about it axis, the induction at the center of the disc is :-
A closely packed coil having $1000$ turns has an average radius of $62.8\,cm$. If current carried by the wire of the coil is $1\,A$, the value of magnetic field produced at the centre of the coil will be (permeability of free space $=4 \pi \times 10^{-7}\,H / m$ ) nearly