Question

如图7-12所示电路,电源电压保持不变,电阻R1=5欧,R2=15欧.

Answer 1

⑴U＝IR总＝0.2A*20欧＝4V⑵S1S2都闭合,R2被短路,R1R3并联I1＝U/R1＝4V/5欧＝0.8AI2＝I-I1＝0.9A-0.8A＝0.1A 23（1）R总＝R1+R2＝30欧+30欧＝60欧I＝U/R＝6V/60欧＝0.1AU2＝IR2＝0.1A*30欧＝3V⑵S闭合后,R2被短路,U2＝0VI＝U/R＝6V/30欧＝0.2A