总电阻 R 要根据三个电阻的连接
1、三电阻串联,R = 10 + 20 + 30 = 60 Ω;
2、三电阻 1/20 + 1/30 = 11/60, R = 60/11 Ω;
3、两只并联,再串联另一只:
R = 10//20 + 30 = 1
或 R = 10//30 + 20 = 55/2 Ω;
或 R = 20//30 + 10 = 22 Ω;
4、两只串联,再并联另一
R = ( 10 +20
或 R = ( 10 +30 )//20 = 40/3 Ω;
或 R = ( 20 +30 )//10 = 25/3 Ω;