The magnetic field at the origin due to the current $I$ flowing in the wire as shown in the figure is:

Consider a long straight wire of a circular cross-section (radius $a$) carrying a steady current $I$. The current is uniformly distributed across this cross-section. The distances from the centre of the wire's cross-section at which the magnetic field [inside the wire,outside the wire] is half of the maximum possible magnetic field,anywhere due to the wire,will be

The magnetic field due to a current-carrying circular loop of radius $5 \ cm$ at a point on the axis at a distance of $12 \ cm$ from the centre is $250 \ \mu T$. The magnetic field at the centre of the loop is (in $\mu T$)

$A$ current of $1\,A$ is flowing through the sides of an equilateral triangle of side $4.5\times10^{-2}\,m$. The magnetic field at the centre of the triangle will be

The magnetic flux passing through the rectangular loop is proportional to:

$A$ Helmholtz coil has a pair of loops,each with $N$ turns and radius $R$. They are placed coaxially at a distance $R$ apart,and the same current $I$ flows through the loops in the same direction. The magnitude of the magnetic field at $P$,the midpoint between the centers $A$ and $C$,is given by (Refer to figure):