( 多选 ) 如图 338 所示电路中, L 为电感线圈, R 为灯泡,电流表内阻为零,电压表内阻无限大,交流电源的电压 u = 220 sin 100π t V ,若保持电压的有效值不变,只将电源频率改为 100 Hz ,下列说法正确的是 ( ) A .电流表示数增大 B .电压表示数增大 C .灯泡变暗 D .灯泡变亮 A.B.C.D. D
【简答题】When we're learning a foreign language, sense of what we hear is the first step toward fluency. It sounds obvious, but until recently, we didn't know much about how listening works. New researc...