交流电-----外文翻译.doc

Alternating Current
An alternating current is one which varies in the circuit with time. The value of the current at any given instant of time is the instantaneous value of current, symbolized by . The instantaneous value of current is deemed positive for one direction of flow though the cross-section of a conductor, and negative for the opposite direction. The direction of current flow in which instantaneous values are positive is called positive. A current is fully specified, if one knows its instantaneous value as a function of time, =F(t),and its positive direction.
Current whose value recur for equal increments of time are called periodic, and the least increment of time for which this recurrent takes place is called the period . For a periodic current = F(t)= F(t+T)
Fig.4.1 shows an example of the relationship = F(t) for a periodic current. The arrow in the diagram indicates the positive direction of current flow. The dotted arrows show the actual direction of current flow at the instants of time when >0 and <0. The segments of the curve between points a and b or O and c cover a complete cycle of current alternations over one period.


交流电
交流电在电路中是一个随时间变化的值。电流值在任何给定的时间上都是一个瞬态值，用符号 表示。当瞬态电流值 从用正号标记的导体的端流进时为正值，而从相反的方向流动时为负值。当电流的任一瞬态值为正时，它流进导体的方向就为正极。假如知道瞬态值与时间的关系式： 以及它的正方向，那么瞬时电流值就是一个定值。
电流值随时间T进行周期性变化的这种现象叫做交流电的周期性，能满足这个条件的最小T值我们把它叫做周期。周期电流的公式为：
= F(t)= F(t+T)
图4.1是 = F(t)周期电流的一个例子。正如图表中箭头所示，指出的方向表示电流的方向。打点的箭头表示瞬时电流的正方向。在曲线上a与b或者o与c之间的部分就表示交流电一个完整的周期。