= Small-loop magnetic radiation resistance
{title2=$R_{\rm rad}=\frac{\mu_0 A^2\omega^4}{6\pi c^3}$}
A fixed electrically small loop of area A with peak sinusoidal current $I_0\cos\omega t$ has magnetic moment $m=AI$. The <magnetic dipole radiation> law gives mean <power> $\mu_0A^2I_0^2\omega^4/(12\pi c^3)$. Defining it as $I_0^2R_{\rm rad}/2$ yields $R_{\rm rad}=\mu_0A^2\omega^4/(6\pi c^3)$. This equivalent resistance accounts for radiation, not heating in the conductor. Rotating the loop changes its vector moment and cannot in general be modelled by the same scalar current alone.
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