Question

If expressions for the magnetic field at a point due to a current element, in C.G.S.system is given by $d\overrightarrow{B}=\frac{{\mu }_0}{4\pi }\frac{i\left(d\overrightarrow{l\times \overrightarrow{r}}\right)}{{a\ast r}^3}$. Find a.

Answer 1

Biot-Savart's law-

$d\overrightarrow{B}=\frac{{\mu }_0}{4\pi }\frac{i\left(d\overrightarrow{l\times \overrightarrow{r}}\right)}{r^3}$

where
$\frac{{\mu }_0}{4\pi }=1$ in CGS system