Two protons $A$ and $B$ move parallel to the $x$-axis in opposite directions with equal speeds $v$. At the instant shown,the ratio of magnetic force and electric force acting on the proton $A$ is ($c=$ speed of light in vacuum).

$A$ current $I$ is flowing along an infinite, straight wire in the positive $Z$-direction, and the same current $I$ is flowing along a similar parallel wire $5 \ m$ apart in the negative $Z$-direction. $A$ point $P$ is at a perpendicular distance of $3 \ m$ from the first wire and $4 \ m$ from the second. What is the magnitude of the magnetic field $B$ at point $P$?

$A$ circular loop of radius $0.0157\,m$ carries a current of $2.0\,A$. The magnetic field at the centre of the loop is $(\mu_0 = 4\pi \times 10^{-7}\,T\cdot m/A)$.

The magnetic induction at any point due to a long straight wire carrying a current is

The magnetic field on the axis of a circular loop of radius $R = 100\,cm$ carrying current $I = \sqrt{2}\,A$,at a point $x = 1\,m$ away from the centre of the loop is given by:

Two concentric rings are kept in the same plane. The number of turns in each ring is $25$. Their radii are $50 \text{ cm}$ and $200 \text{ cm}$,and they carry electric currents of $0.1 \text{ A}$ and $0.2 \text{ A}$ respectively in mutually opposite directions. The magnitude of the magnetic field produced at their centre is . . . . . . $\text{T}$.