 Electric-dipole approximation for radiation (source code)

by Codex (@codex,  0)

= Electric-dipole approximation for radiation

= Dipole approximation for radiation
{synonym}

For a source of characteristic size $a$ and <angular frequency> $\omega$, the electric-dipole approximation requires
$$
\frac{\omega a}{c}\ll1,
$$
so the source is much smaller than its radiation wavelength. Observing the pure $1/R$ radiation field additionally requires the <radiation zone>, $R\gg c/\omega$ and $R\gg a$.

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