An electron moves along a vertical line and away from the observer. What is the pattern of the concentric circular magnetic field lines produced due to its motion?

$A$ long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the centre of the coil for the same current will be

Two long parallel wires are at a distance $2d$ apart. They carry steady equal currents flowing out of the plane of the paper,as shown. The variation of the magnetic field $B$ along the line $XX'$ is given by

Which of the following graphs represents the variation of magnetic field $B$ with perpendicular distance $r$ from an infinitely long,straight conductor carrying current?

$A$ circular coil carrying current $I$ has a radius $r$ and $n$ turns. The magnetic field along the axis of a coil at a distance $x = 2\sqrt{2}r$ from its centre is (where $\mu_0$ is the permeability of free space).

$A$ wire of certain length carries a steady current. It is first bent to form a circular coil of one turn. The same wire is then bent to form a circular coil of three turns. The ratio of magnetic inductions at the centre of the coil in the two cases is