在研究静电场的性质时,提出并定义了电势、电势差和电压等概念。在许多电磁学教科书中,这些概念往往立即被引用到其它各章节,而不加任何说明。这时,如果我们不能清醒地注意到概念的适用范围,那末势必造成混乱或导致荒谬。下面就是一个典型的例子。在闭合线圈中,因磁通量的变化而产生如图所示的感生电流。问:线圈上的A、B两点,哪一点的电势高?如果试图从电荷移动的方向上去判断A、B电势的高低,那是永远得不出结论的。好比问: In the study of the nature of the electrostatic field, concepts such as potential, potential difference, and voltage were proposed and defined. In many electromagnetic textbooks, these concepts are often immediately cited in other chapters without any explanation. At this time, if we can’t soberly notice the scope of application of the concept, then it is bound to cause confusion or lead to absurdity. Here is a typical example. In the closed coil, an induced current as shown in the figure is generated due to the change of the magnetic flux. Question: What are the points at the two points A and B on the coil? If you try to determine the potentials of A and B from the direction of the charge movement, you can never reach a conclusion. It’s like asking: