= Perfect-conductor sphere dipole interference
{title2=$\sigma_{\rm back}=9\pi k^4a^6$}
An electrically small <perfect conductor> sphere has both an induced <electric dipole moment> and <magnetic dipole moment>. The latter contributes half the electric scattering <amplitude> in magnitude. The two <amplitudes> add in the backward direction and partially cancel in the forward direction. Thus the backward intensity is $9/4$ of the electric-only value and its <radar cross section> is $9\pi k^4a^6$. The correction persists at leading order as $ka\to0$; discarding the magnetic term is a separate response approximation.<Scattering of EM Waves by Michael Fowler>[Scattering by a Small Perfectly Conducting Sphere]{ref}
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