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The velocity factor (VF),〔Gottlieb, I.M., ''Practical RF power design techniques'', TAB Books, 1993, ISBN 0-8306-4129-7, p.251 ('velocity factor')〕 also called wave propagation speed or velocity of propagation (VoP or ),〔''(Velocity of Propagation )'', General Cable Australia Pty Ltd, retrieved 2010-02-13〕 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. The speed of radio signals in a vacuum, for example, is the speed of light, and so the velocity factor of a radio wave in a vacuum is unity, or 100%. In electrical cables, the velocity factor mainly depends on the insulating material (see table below). The use of the terms ''velocity of propagation'' and ''wave propagation speed'' to mean a ratio of speeds is confined to the computer networking and cable industries. In a general science and engineering context, these terms would be understood to mean a true speed or velocity in units of distance per time,〔"velocity of propagation" in Walker, P.M.B., ''Chambers Science and Technology Dictionary, Edinburgh, 1991, ISBN 1-85296-150-3〕 while ''velocity factor'' is used for the ratio. == Typical velocity factors == Velocity factor is an important characteristic of communication media such as Category 5 cables and radio transmission lines. Plenum data cable typically has a VF between 0.42 and 0.72 (42% to 72% of the speed of light) and riser cable around 0.70. A VF of 0.70 corresponds to a speed of approximately 210,000,000 m/s or 4.76 ns to travel one meter. Some typical velocity factors for radio communications cables provided in handbooks and texts are: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Velocity factor」の詳細全文を読む スポンサード リンク
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