Magnetic induction is a

The magnetic field at a point $P$ situated at a perpendicular distance $R$ from a long straight wire carrying a current of $12 \ A$ is $3 \times 10^{-5} \ Wb/m^2$. The value of $R$ in $mm$ is $\left[\mu_0 = 4\pi \times 10^{-7} \ Wb/Am\right]$

Two straight horizontal parallel wires are carrying the same current in the same direction, and $d$ is the distance between the wires. You are provided with a small freely suspended magnetic needle. At which of the following positions will the orientation of the needle be independent of the magnitude of the current in the wires?

An arc of a circle of radius $R$ subtends an angle $\frac{\pi}{2}$ at the centre. It carries a current $I$. The magnetic field at the centre will be ($\mu_0 =$ permeability of free space).

$A$ current $I$ flows through the loop as shown in the figure. The magnetic field at the centre $O$ is:

$A$ 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: