In a medium with relative permeability μr=4 and relative permittivity εr=9, the electric field is described by E(x,t)=150sin(1.5×107x−ωt)N C−1. Calculate the angular frequency ω (in rad s⁻¹) required so that the expression represents a plane electromagnetic wave propagating in that medium. (c=3.0×108m s−1)
(a) 1.5×1015
(b) 4.5×1015
(c) 7.5×1014
(d) 1.3×1014