$A$ circular coil of wire consisting of $100$ turns,each of radius $8.0 \, cm$,carries a current of $0.40 \, A$. What is the magnitude of the magnetic field $B$ at the centre of the coil?

Two identical circular wires of radius $20\,cm$ and carrying current $\sqrt{2}\,A$ are placed in perpendicular planes as shown in the figure. The net magnetic field at the centre of the circular wires is $.............\times 10^{-8}\,T$. (Take $\pi=3.14$ )

$A$ long straight wire of radius $r$ carries a steady current $I$. The current is uniformly distributed over its cross-section. The ratio $\left(\frac{B}{B^1}\right)$ of the magnetic field $B$ and $B^1$ at radial distances $\frac{r}{2}$ and $3r$ respectively,from the axis of the wire is:

$PQRS$ is a square loop made of a uniform conducting wire. The current enters the loop at $P$ and leaves at $S$. Then the magnetic field will be

The ratio of the magnetic field at the centre of a current-carrying circular wire and the magnetic field at the centre of a square coil made from the same length of wire will be

Four identical long solenoids $A, B, C$ and $D$ are connected to each other as shown in the figure. If the magnetic field at the center of $A$ is $3\, T$,the field at the center of $C$ would be........... $T$ (Assume that the magnetic field is confined within the volume of the respective solenoid).