Question

【题目】电阻R1=15Ω，R2=10Ω，R3=5Ω，下列连接电阻最小的是（ ）
A.只能用R3
B.R1与R3并联
C.R2与R3并联
D.R1、R2与R3并联

Answer 1

【答案】D
【解析】解：因并联电路中总电阻的倒数等于各分电阻倒数之和，
所以，R1与R3并联时有 = + = + = ，解得R13=3.75Ω，
R2与R3并联时有 = + = + = ，解得R23≈3.33Ω，
R1、R2与R3并联时有 = + + = + + = ，解得R123≈2.73Ω，
综上可知，D选项的电阻最小．
故选D．
根据电阻的并联求出R1与R3并联、R2与R3并联、R1、R2与R3并联后的总电阻，然后与R3的阻值比较得出答案．