fázissebessége

Phase velocity refers to the speed at which the phase of a wave propagates in space. It is a fundamental concept in wave physics and is distinct from the group velocity, which describes the speed of the overall envelope of a wave packet. For a simple sinusoidal wave, the phase velocity is the speed at which a point of constant phase, such as a crest or trough, travels. Mathematically, it is often expressed as the ratio of the wave's angular frequency (ω) to its wave number (k), i.e., vp = ω/k. The units of phase velocity are typically distance per time, such as meters per second. In some media, the phase velocity can be greater than the speed of light in a vacuum, but this does not violate the principles of special relativity because information or energy cannot be transmitted at this speed. The phase velocity depends on the properties of the medium through which the wave is traveling and can vary with the frequency of the wave, a phenomenon known as dispersion. When the phase velocity is independent of frequency, the medium is considered non-dispersive.