Bài 3:

a) \(R_{td}=\dfrac{R_1.R_2}{R_1+R_2}=\dfrac{20.20}{20+20}=10\Omega\)

b)\(\dfrac{1}{R_{td}}=\dfrac{1}{R_1}+\dfrac{1}{R_2}+\dfrac{1}{R_3}=\dfrac{1}{20}+\dfrac{1}{20}+\dfrac{1}{15}=\dfrac{1}{6}\\ =>R_{td}=6\Omega\)

c) \(U=U_1=U_2=30\left(V\right)\)

=> \(I=\dfrac{U}{R_{td}}=\dfrac{30}{6}=5\left(A\right)\)

=> \(I_1=\dfrac{U_1}{R_1}=\dfrac{30}{20}=1,5\left(A\right)\)

Mà \(R_1=R_2=20\Omega\)

=> \(I_1=I_2=1,5\left(A\right)\)

=> \(I_3=I-I_1-I_2=5-1,5-1,5=2\left(A\right)\)

\(V_{tb}=\dfrac{S_1+S_2}{t_1+t_2}=\dfrac{400+160}{40+40}=7\left(\dfrac{m}{s}\right)\)

a) \(R_{td}=\dfrac{R_1.R_2}{R_1+R_2}=\dfrac{30.60}{30+60}=20\Omega\)
b)\(U=U_1=U_2=12\left(V\right)\)
=> \(I=\dfrac{U}{R_{td}}=\dfrac{12}{20}=0,6\left(A\right)\)

=> \(I_1=\dfrac{U_1}{R_1}=\dfrac{12}{30}=0,4\left(A\right)\)

=> \(I_2=I-I_1=0,6-0,4=0,2\left(A\right)\)

I + R₁= ??? Nhân chứ nhỉ