The magnetic field $d\overrightarrow{B}$ due to a small current element $d\overrightarrow{l}$ at a distance $\overrightarrow{r}$ from an element carrying current $i$ is given by:

  • A
    $d\overrightarrow{B} = \frac{\mu_0}{4\pi} i \left( \frac{d\overrightarrow{l} \times \overrightarrow{r}}{r} \right)$
  • B
    $d\overrightarrow{B} = \frac{\mu_0}{4\pi} i^2 \left( \frac{d\overrightarrow{l} \times \overrightarrow{r}}{r} \right)$
  • C
    $d\overrightarrow{B} = \frac{\mu_0}{4\pi} i^2 \left( \frac{d\overrightarrow{l} \times \overrightarrow{r}}{r^2} \right)$
  • D
    $d\overrightarrow{B} = \frac{\mu_0}{4\pi} i \left( \frac{d\overrightarrow{l} \times \overrightarrow{r}}{r^3} \right)$

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