bài 3:
a) Điện trở tương đương:
\(R_{Td}=\dfrac{R_1R_2}{R_1+R_2}=\dfrac{4.12}{4+12}=3\Omega\)
b) U=\(R_{td}.I=3.2=6\left(V\right)\)
c) ta có: U=U1=U2=6V
=> I1=\(\dfrac{U_1}{R_1}=\dfrac{6}{4}=1,5\left(A\right)\)
=> I=I1+I2
=> I2= I- I1=\(2-1,5=0,5\left(A\right)\)
Bài 4:
\(R_{td}=\dfrac{R_1R_2}{R_1+R_2}=\dfrac{8.12}{8+12}=4,8\Omega\)
b) \(U=I.R_{td}=1,5.4,8=7,2\left(V\right)\)
c) U=U1=U2=7,2(V)
=> \(I_1=\dfrac{U_1}{R_1}=\dfrac{7,2}{8}=0,9\left(A\right)\)
I= I1 +I2 => I2= I - I1= 1,5-0,9=0,6(A)


