The magnetic field at the point of intersection of diagonals of a square wire loop of side $L$ carrying a current $I$ is

Two identical circular loops $P$ and $Q$ each of radius $r$ are lying in parallel planes such that they have a common axis. The currents through $P$ and $Q$ are $I$ and $4I$ respectively in the clockwise direction as seen from $O$. The net magnetic field at $O$ is:

$A$ coil having $100$ turns is wound tightly in the form of a spiral with inner and outer radii $1 \text{ cm}$ and $2 \text{ cm}$,respectively. When a current $1 \text{ A}$ passes through the coil,the magnetic field at the centre of the coil is

$20 \, A$ current is flowing in a long straight wire. The intensity of the magnetic field at a distance of $20 \, cm$ from the wire will be:

The magnetic induction at a point $P$ which is distant $4 \, cm$ from a long current-carrying wire is $10^{-8} \, T$. The magnetic field induction at a distance $12 \, cm$ from the same current would be:

$A$ 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