On-axis magnetic field of a circular current loop
= On-axis magnetic field of a circular current loop
A circular loop of radius $R$ carrying <electric current> $I$ has, on its axis,
$$
B(z)=\frac{\mu_0IR^2}{2(R^2+z^2)^{3/2}}\,\hat z,
$$
where the sign of $\hat z$ is fixed by the <right-hand rule>. At its centre, $B(0)=\mu_0I/(2R)$.