$A$ circular loop of radius $R$ is carrying current $I$. The ratio of the magnetic field at the center of the circular loop to the magnetic field at a distance $R$ from the center of the loop on its axis is:

$A$ current of $4 \ A$ is passed through a square loop of side $5 \ cm$ made of a uniform manganin wire as shown in the figure. The magnetic field at the centre of the loop is

$A$ horizontal overhead power line carries a current of $90 \;A$ in east to west direction. What is the magnitude and direction of the magnetic field due to the current $1.5 \;m$ below the line?

The magnitude of the magnetic field at the centre of an equilateral triangular loop of side $1\,m$ which is carrying a current of $10\,A$ is:......$\mu T$ [Take $\mu _0 = 4\pi \times 10^{-7}\,NA^{-2}$]

As shown in the figure,two infinitely long straight parallel wires $P$ and $Q$ carrying equal currents in opposite directions are arranged parallel to the $Y$-axis. If the magnetic field due to wire $P$ at the origin '$O$' of the coordinate system is $B$,then match the resultant magnetic fields at various points given in Column $A$ with the points given in Column $B$.

Column $A$	Column $B$
$A) \frac{B}{4}$	$i) (0, 0)$
$B) \frac{B}{2}$	$ii) (a, 0)$
$C) \frac{2B}{3}$	$iii) (2a, 0)$
$D) 2B$	$iv) (3a, 0)$

$A$ horizontal overhead powerline is at a height of $4\,m$ from the ground and carries a current of $100\,A$ from east to west. The magnetic field directly below it on the ground is $\left( {{\mu _0} = 4\pi \times {{10}^{ - 7}}} \right)TmA^{-1}$.