câu 4
TH1: Uab=10V,Ucd=4V
=> R1 //(R2 nt R3)
\(=>R2=\dfrac{4}{I2}=4\Omega\),\(=>R3=\dfrac{10-4}{I3}=6\Omega\)
TH2: Ucd=6V,Uab=1,5V=>R2//(R1 nt R3)
\(=>R1=\dfrac{1,5}{I1}=\dfrac{1,5}{\dfrac{6-1,5}{6}}=\dfrac{1,5}{\dfrac{3}{4}}=2\Omega\)
câu 5
{R3 nt(R1//R2)}//R4
\(=>Rtd=\dfrac{R4\left\{R3+\dfrac{R1R2}{R1+R2}\right\}}{R3+R4+\dfrac{R1R2}{R2+R1}}=15\Omega\)
\(=>Ia=I2+I4\)
ta đi tính I2 và I4
\(=>U4=U123=U=30V=>I4=\dfrac{30}{30}=1A\)
\(=>I123=\dfrac{30}{R3+\dfrac{R1R2}{R1+R2}}=1A=I12=>U12=R12=\dfrac{4}{5}V=U2=>I2=\dfrac{U2}{R2}=\dfrac{1}{5}A\)
\(=>Ia=\dfrac{1}{5}+1=\dfrac{6}{5}A\)
