(1)S2断开时,S1拨到B处,A、A1串联A=A1=6V/4Ω+6Ω=0.6A
(2)S2闭合时,S1拨到A时,R1、R2并联A测总电流6V/(R1×R2/R1+R2)=4A,A1测R1电流并联分流电压不变6V/6Ω=1A