$A$ and $B$ are two concentric circular conductors of centre $O$ and carrying currents ${i_1}$ and ${i_2}$ as shown in the adjacent figure. If ratio of their radii is $1 : 2$ and ratio of the flux densities at $O$ due to $A$ and $B$ is $1 : 3$, then the value of ${i_1}/{i_2}$ is
$\frac{1}{6}$
$\frac{1}{4}$
$\frac{1}{3}$
$\frac{1}{2}$
Magnitude of magnetic field (in $SI$ units) at the centre of a hexagonal shape coil of side $10\, cm$, $50$ turns and carrying current $I$ (Ampere) in units of $\frac{\mu_{0} I}{\pi}$ is
.......$A$ should be the current in a circular coil of radius $5\,cm$ to annul ${B_H} = 5 \times {10^{ - 5}}\,T$
Which of the field patterns given below is valid for electric field as well as for magnetic field?
An $\alpha$ particle is moving along a circle of radius $R$ with a constant angular velocity $\omega $. Point $A$ lies in the same plane at a distance $2R$ from the centre. Point $A$ records magnetic field produced by $\alpha$ particle. If the minimum time interval between two successive times at which $A$ records zero magnetic field is $‘t’,$ find the angular speed $\omega $, in terms of $t.$