$A$ long thin hollow metallic cylinder of radius '$R$' carries a current '$i$'. The magnetic induction '$B$' at a distance '$r$' from the axis varies as shown in:

At what distance from a long straight wire carrying a current of $12 \, A$ will the magnetic field be equal to $3 \times 10^{-5} \, Wb/m^2$?

$A$ 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:

$A$ straight conductor carries a current of $5 \, A$. An electron travelling with a speed of $5 \times 10^6 \, m/s$ parallel to the wire at a distance of $0.1 \, m$ from the conductor,experiences a force of:

The figure shows two semicircular loops of radii $R_1$ and $R_2$ carrying current $I$. The magnetic field at the common centre '$O$' is

Current $I$ is flowing in a conductor shaped as shown in the figure. The radius of the curved part is $r$ and the length of the straight portions is very large. The value of the magnetic field at the centre $O$ will be