The magnetic induction due to an infinitely long straight wire carrying a current $i$ at a distance $r$ from the wire is given by:

• A
  $|B| = \left( \frac{\mu_0}{4\pi} \right) \frac{2i}{r}$
• B
  $|B| = \left( \frac{\mu_0}{4\pi} \right) \frac{r}{2i}$
• C
  $|B| = \left( \frac{4\pi}{\mu_0} \right) \frac{2i}{r}$
• D
  $|B| = \left( \frac{4\pi}{\mu_0} \right) \frac{r}{2i}$