Question

The direction of induced magnetic field $d\vec{B}$ due to current element $id\vec{L},$ at a point of distance $r$ from it, when a current $i$ passes through a long conductor is in the direction

• A. of position vector $\vec{r}$ of the point
• B. of current element $d\vec{L}$
• C. perpendicular to both $d\vec{L}$ and $\vec{r}$
• D. perpendicular to $\vec{L}$ only

Answer 1

Answer: (C)

Biot- Savart law states
$d\vec{B}=\frac{{\mu }_0}{4\pi }\frac{id\vec{L}\times \vec{r}}{r^3}$
$\therefore$ Direction of $d\vec{B}$ is perpendicular to both $d\vec{L}$ and $\vec{r}$