i() i(t)rdt R W=IRT IRTE o (t)Rdt R (t)dt 同样,可定义电压有效值 def u(t)di 0W2=I 2RT R i(t) R I 同样，可定义电压有效值：  = T W i t R t 0 2 1 ( ) d  = T I RT i t R t 0 2 2 ( ) d  = T i t t T I 0 2 ( )d 1  = T u t t T U 0 2 def ( )d 1