Câu 4a) Vì R1 nt (R2//R3)
=>R23=R2.R3/R2+R3 =100.150/100+150 =60(ôm)
RAB=Rtđ=R23+R1=40+60=100 (ôm)
b) iab=Uab/Rab=90/100 =0,9 (A)
Vì R1 nt (R2//R3) =>iab=i1=i23=i2+i3=0,9 (A)
theo đl ôm ta có U2/R2 =i2 ;i3=U3/R3; vì R2//R3 =>U2=U3
=>i2+i3=U2/R2 + U3/R3 =U2/100 + U3/150 =U2 (1/100 +1/150)...