$A$ current of $10\,A$ is passing through a long wire which has a semicircular loop of radius $20\,cm$ as shown in the figure. The magnetic field produced at the centre $P$ of the loop is:

$A$ steady electric current is flowing through a cylindrical wire. Which of the following statements is/are correct?
$(a)$ The electric field at the axis of the wire is zero.
$(b)$ The magnetic field at the axis of the wire is zero.
$(c)$ The electric field in the vicinity of the wire is zero.
$(d)$ The magnetic field in the vicinity of the wire is zero.

Two parallel wires of equal lengths are separated by a distance of $3 \ m$ from each other. The currents flowing through the $1^{\text{st}}$ and $2^{\text{nd}}$ wires are $3 \ A$ and $4.5 \ A$ respectively in opposite directions. Find the resultant magnetic field at the midpoint between the wires $(\mu_0 = \text{permeability of free space})$.

As shown in the figure,a current of $2\,A$ flows in an equilateral triangle of side $4 \sqrt{3}\,cm$. The magnetic field at the centroid $O$ of the triangle is:
(Neglect the effect of the earth's magnetic field.)

$\frac{V \cdot s}{A \cdot m}$ is the unit of which physical quantity?

The figure shows two semicircular loops of radii $R_1$ and $R_2$ carrying current $I$. The magnetic field at the common centre '$O$' is