Velocity factor
（重定向自Velocity of Propagation）
The velocity factor (VF), also called wave propagation speed or velocity of propagation (VoP or ![v_\mathrm{P}](/Images/godic/202502/19/c382c31f9c7763eec57ff98d0392281f2536.png")
), of a transmission medium is the ratio of the speed at which a wavefront (of an acoustic signal, for example, or an electromagnetic signal, a radio signal, a light pulse in a fibre channel or a change of the electrical voltage on a copper wire) passes through the medium, to the speed of light in a vacuum. For optical signals, the velocity factor is the reciprocal of the refractive index.