Biot-Savart law indicates that the moving electrons (velocity $\vec{v}$) produce a magnetic field $\vec{B}$ such that

Two identical long parallel wires carry currents $I_1$ and $I_2$ such that $I_1 > I_2$. When the currents are in the same direction,the magnetic field at a point midway between the wires is $8 \times 10^{-6} \ T$. If the direction of $I_2$ is reversed,the field becomes $3.2 \times 10^{-5} \ T$. The ratio of $I_2$ to $I_1$ is

Find the magnetic field at point $P$ in the given diagram.

$A$ circular coil of wire of radius $r$ has $n$ turns and carries a current $I$. The magnetic induction $B$ at a point on the axis of the coil at a distance $\sqrt{3} r$ from its centre is

$A$ wire bent in the shape of a regular $n$-polygonal loop carries a steady current $I$. Let $l$ be the perpendicular distance of a given segment and $R$ be the distance of a vertex from the centre of the loop. The magnitude of the magnetic field at the centre of the loop is given by

$A$ 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: