The magnetic field at a distance $r$ from a long wire carrying current $i$ is $0.4\, Tesla$. The magnetic field at a distance $2r$ is......$Tesla$

A part of a long wire carrying a current $i$ is bent into a circle of radius $r$ as shown in figure. The net magnetic field at the centre $O$ of the circular loop is

Assertion : A charge, whether stationary or in motion produces a magnetic field around it.

Reason : Moving charges produce only electric field in the surrounding space.

An element $\Delta l=\Delta \mathrm{xi}$ is placed at the origin and carries a large current $\mathrm{I}=10 \mathrm{~A}$. The magnetic field on the $y$-axis at a distance of $0.5 \mathrm{~m}$ from the elements $\Delta \mathrm{x}$ of $1 \mathrm{~cm}$ length is:

A current of $0.1\, A$ circulates around a coil of $100$ $turns$ and having a radius equal to $5\, cm$. The magnetic field set up at the centre of the coil is $({\mu _0} = 4\pi \times {10^{ - 7}}\,weber/ampere - metre)$

Write equation of magnetic field due to a circular current carrying loop at a point on the axis of the loop. Give its special cases.