$A$ closely wound solenoid of $800$ turns and area of cross section $2.5 \times 10^{-4} \text{ m}^2$ carries a current of $3.0 \text{ A}$. The magnetic moment associated with it is . . . . . . . (in $\text{ JT}^{-1}$)

The magnetic field at the centre of a current carrying circular coil of area $A$ is $B$. The magnetic moment $(M)$ of the coil is $(\mu_0 = \text{permeability of free space})$

$A$ charge $q$ is spread uniformly over an isolated ring of radius $R$. The ring is rotated about its natural axis with an angular velocity $\omega$. Magnetic dipole moment of the ring is

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

In an atom,an electron of charge $(-e)$ performs uniform circular motion ($U$.$C$.$M$.) around a stationary positively charged nucleus with a period of revolution $T$. If $r$ is the radius of the orbit of the electron and $v$ is the orbital velocity,then the circulating current $I$ is proportional to:

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: