坡印廷定理的再思考

Rethinking of Poynting’s Theorem

摘要: 本文通过研究直流以及低频交流电能的传输过程，指出在电磁学问题中，除了由坡印亭矢量定义的电磁能流外，还有一种“经典”的能量传输过程：电路内部的大量自由电子在电源电动势的驱动下运动，电源的电动势能转化为自由电子的动能。在导线外，由于几乎没有自由电子，因此没有形成电流。在直流电路以及低频交流电路，导线内的电能的传输过程与位移电流无关，也与坡印亭定理无关。集总电路模型是不计算导线长度的，它隐含了一个假定：低频交变电信号在导线中的速度是无穷大。我们的实验结果表明，在特定条件下交变电信号在导线中的速度可以超光速，这是对集总参数电路模型的改进。

Abstract: In this paper, we study the energy transmission process of direct current and low frequency alternating current. We point out that in addition to the electromagnetic energy flow defined by Poynting vector, there is a “classical” energy transfer process: free electrons driven by the electromotive force of the power supply. The electromotive force of the power supply can be converted into kinetic energy. Outside wires, no current is formed because there are no free electrons. In the case of DC circuits and low-frequency AC circuits, the transfer of electric energy in wires is not related to the displacement current, so it is also independent of the Poynting theorem. The model of lumped element circuit does not calculate the length of the wire. Indeed, it implies an assumption: the speed of low-frequency alternating signals in the wire is infinite. Our experimental results show that under certain conditions, the speed of alternating electrical signals in the wire can be much greater than the speed of light, which is an improvement on the model of lumped parameter circuit.