电路是由元件组成的,因此在分析电路之前,必须弄清楚每个元件的特性。
分析元件的特性首先是弄清楚这个元件的电压和电流关系,简称伏安关系。然后要弄清楚这个元件对于电能是如何处理的,是消耗电能转化为其他能量,还是由其他能量转化为电能;是一直消耗电能还是消耗与发出电能交替进行。
① 电阻R因其阻碍电荷移动而得名,常用于调整电流大小。电阻R的电压u和电流i的实际方向永远是关联的,故电阻是消耗电功率的,其功率p永远非负。若电路中电阻R的电压和电流i的参考方向是关联的,则u=+iR;若参考方向是非关联的,那么u=-iR。
②电感L得名于其工作机理是电磁感应。电流i变化时产生变化的磁场,变化的磁场又在线圈中产生感应电动势和感应电流,这个感应电流会产生反向的磁场去抵消原磁场的变化(楞次定律)。由此可以看出,电感有阻碍电流变化,维持电流不变的作用。
电感L的电流变化越快,即频率越大,则产生的阻碍作用越强,表现为感应电动势e越大,即电感电压u大。注意:感应电压u和感应电动势e是大小相同,方向相反的。
电感L不消耗能量,可以吸收电能转化为磁场能,也可以将储存的磁场能转化为电能,表现为其功率p可正可负。
③电容C得名于其两块金属板上可储存的电荷。金属板存储的电荷在板间形成电压。当电荷数量q改变,则电压改变。而增多的电荷或者减少的电荷是通过与金属板相连的导线移动,故在导线上形成电流。
电压变化的快,即电荷q变化的快,导线上的电流就大(电流是单位时间内通过的电荷数量)。
电容C可以吸收电能转化为电场能,也可以将储存的电场能转化为电能,本身不消耗电能,和电感L一样,其功率p也可正可负。
④理想电压源Us是一个输出电压恒定不变的电源。无论有没有接负载,无论接多大的负载,输出电压恒定不变。但接负载不同,其输出电流可大可小,可正可负。
实际电压源是含有内阻的电压源,表现为输出电压略低于其开口电压,接负载不同,低于开口电压的程度也不同。
⑤理想电流源Is是一个输出电流恒定不变的电源。无论是短路时的电流,还是接负载时的电流,均为Is。但接负载不同时,其输出电压不同,可大可小,可正可负。
实际电流源是含有内阻的电流源,表现为输出电流略低于短路电流,且负载不同,低于短路电流的程度不同。


































该内容转载自河科大牛老师,仅供学习交流使用,如有侵权,请联系删除。