Among the following,the unit of permeability is $NOT$ represented by

$A$ square frame of side $1 \ m$ carrying a current $I$ produces a magnetic field $B$ at its centre. The same current is passed through a circular coil having the same perimeter as the square. The magnetic field at the centre of the circular coil is $B^{\prime}$. The ratio of $\frac{B}{B^{\prime}}$ is

Describe and illustrate the magnetic field lines produced by a current-carrying circular loop.

$A$ long straight wire of circular cross-section of radius $a$ is carrying a steady current. The current is distributed uniformly across the cross-section of the wire. The ratio of the magnetic fields at points $0.5a$ and $1.5a$ from the centre of the wire is

Consider two infinitely long wires parallel to the $Z$-axis carrying the same current $I$ in the positive $Z$-direction. One wire passes through point $L$ at coordinates $(-1, 1)$ and the other wire passes through point $M$ at coordinates $(-1, -1)$. The resultant magnetic field at the origin $O$ will be

$A$ straight wire carrying a current $10\, A$ is bent into a semicircular arc of radius $5\, cm.$ The magnitude of the magnetic field at the center is