Question

The direction of induced magnetic field $ d\,\vec{B} $ due to current element $ i d \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
$d \vec{B}=\frac{\mu_{0}}{4 \pi} \frac{i d \vec{L} \times \vec{r}}{r^{3}}$
$\therefore $ Direction of $d \vec{B}$ is perpendicular to both $d \vec{L}$ and $\vec{r}$