Vol.5 No.5 (September 2015)
EM Wave Propagation Speed, Comments on “Measurement of Time Delay of Alternating Electrical Field in Wires” and “Physical Principles of Measuring the Speed of Alternating Electrical Field”
The time shift of an electromagnetic wave at a single frequency between a transmitter and a re-ceiver can be used to determine the phase velocity of the wave propagation only if there is no reflection at the receiver or the reflection is very small. The reflection adds additional phase shifts to the composted wave of an incident wave and a reflected wave so that the time difference of the composted wave is shifted between the transmitter and the receiver. This time difference may be either decreased or increased and even negative in a certain condition. Ignoring the phase shift and time shift induced by the reflection, the authors of two articles recently published on “Modern Physics” wrongly claim of “the speed of alternating electric field can be 20 times faster than the speed of light”. The two articles are: “Measurement of Time Delay of Alternating Electrical Field in Wires” (Modern Physics, 2015, 5, 29-34) and “Physical Principles of Measuring the Speed of Alternating Electrical Field” (Modern Physics, 2015, 5, 35-39). In this communication note, theory and experiments are presented to falsify their claim.
郑翊 , 徐骋 , 牟晋君 (2015) 电磁场的传播速度，评论“导线中交流电场时间延迟的测定”和“交变电场速度测量的物理原理”。 现代物理， 5， 114-123. doi: 10.12677/MP.2015.55015
 张操, 廖康佳, 樊京 (2015) 导线中交流电场时间延迟的测定. 现代物理, 5, 29-34.
 张操, 廖康佳 (2015) 交变电场速度测量的物理原理. 现代物理, 5, 35-39.
 Shen, L.C. and Kong, J.A. (1995) Applied electromagnetism. 3rd Edition, PWS Publishing Company, Boston.
 Ulaby, F.T., Michielssen, E. and Ravaioli, U. (2010) Fundamentals of applied electromagnetics, 6/E. Prentice Hall, Upper Saddle River.
 Calculating the propagation delay of coaxial cable. http://www.gpssource.com/files/Cable-Delay-FAQ.pdf
 Round wire inductance calculator. http://chemandy.com/calculators/round-wire-inductance-calculator.htm
Wang, R., Zheng, Y. and Yao, Y. (2004) Generalized Sagnac effect. Physical Review Letters, 93, Article ID: 143901.
Wang, R.Y., Zheng, Y., Yao, A.P. and Langley, D. (2003) Modified Sagnac experiment for measuring travel-time difference between counter-propagating light beams in a uniformly moving fiber. Physics Latter A, 312, 7-10.