Two thick wires and two thin wires,all of the same material and same length,form a square in three different ways $P, Q,$ and $R$ as shown in the figure with the current connection indicated. The magnetic field at the centre of the square is zero in cases:

$A$ charged particle going around in a circle can be considered to be a current loop. $A$ particle of mass $m$ carrying charge $q$ is moving in a plane with speed $v$ under the influence of magnetic field $\overrightarrow{ B }$. The magnetic moment of this moving particle is:

The radius of a circular loop is $r$ and a current $i$ is flowing in it. The equivalent magnetic moment will be

$A$ small bar magnet experiences a torque of $0.016 \ Nm$ when placed with its axis at $30^{\circ}$ with an external magnetic field of $0.04 \ T$. If the bar magnet is replaced by a solenoid of cross-sectional area $1 \ cm^2$ and $1000$ turns, having the same magnetic moment as that of the bar magnet, then the current flowing through the solenoid is: (in $A$)

An electron in a circular orbit of radius $0.05 \,nm$ performs $10^{16}$ revolutions per second. What is the magnetic moment due to the rotation of the electron? $(e = 1.6 \times 10^{-19} \,C)$

$A$ circular and a square coil are prepared from two identical metal wires and a current is passed through them. The ratio of the magnetic dipole moment associated with the circular coil to that with the square coil is