The magnetic field at a point on the axis of a current element (i.e., along the direction of $d\vec{l}$) is:

The SI unit of magnetic field is:

The magnetic field at a perpendicular distance $d$ from an infinitely long straight wire carrying current $I$ is:

A semi-infinite wire (extending from a point to infinity in one direction) carries current $I$. The magnetic field at a perpendicular distance $d$ from the end of the wire is:

The Biot-Savart law gives the magnetic field due to a current element as $d\vec{B} = \frac{\mu_0}{4\pi}\frac{Id\vec{l} \times \hat{r}}{r^2}$. The magnetic field $dB$ is maximum when the angle between $d\vec{l}$ and $\hat{r}$ is: