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 \(R_1=R_2=20\Omega\)
=> \(I_1=I_2=1,5\left(A\right)\)
=> \(I_3=I-I_1-I_2=5-1,5-1,5=2\left(A\right)\)
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