Symbol ωp. The frequency of plasma oscillations in an equilibrium charge distribution. The Langmuir frequency is given by ωp = (4πneq2/m)½ = 5.7 × 105 ne½ (radians/sec), where ne is the density of electrons and m and q are the mass and charge, respectively, of the electron. The Langmuir frequency is named after the US chemist Irving Langmuir (1881–1957), who derived the expression in 1928 in his analysis of plasma oscillations by combining Poisson's equation with Newton's law of motion. The Langmuir frequency can also be derived using quantum mechanics for the electron gas.