Transverse wave cutoff in a cold unmagnetized plasma
= Transverse wave cutoff in a cold unmagnetized plasma
With immobile ions, negligible collisions and electron density $n_e$, the <plasma frequency> is $\omega_p^2=n_ee^2/(m_e\epsilon_0)$. Combining inertial electron current with vacuum <displacement current> gives $\omega^2=\omega_p^2+c^2k^2$. Transverse fields are evanescent below $\omega_p$ and propagate above it.