  A uniformly-charged spherical shell of radius $R$, mass $m$, and total
electrical charge $q$, having an oscillatory angular velocity $\Omega(t)$
around a fixed axis, is a model for a magnetic dipole that radiates an
electromagnetic field into its surrounding free space at a fixed oscillation
frequency $\omega$. An exact solution of the Maxwell-Lorentz equations of
classical electrodynamics yields the self-torque of radiation resistance acting
on the spherical shell as a function of $R$, $q$, and $\omega$. Invoking the
Newtonian equation of motion for the shell, we relate its angular velocity
$\Omega(t)$ to an externally applied torque, and proceed to examine the
response of the magnetic dipole to an impulsive torque applied at a given
instant of time, say, $t=0$. The impulse response of the dipole is found to be
causal down to extremely small values of $R$ (i.e., as $R \to 0$) so long as
the exact expression of the self-torque is used in the dynamical equation of
motion of the spherical shell.
