Cho mach dien nhu hinh ve , biet R1=R2=R3=R4=R5=5 OM, R6=6 OM , U=6 OM . Tinh U4
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Ta có :R12=R1+R2=10+10=20\(\Omega\)
Có :(R1nt R2)//R3 :
\(\Rightarrow\)R123=\(\frac{R_{12}.R_3}{R_{12}+R_3}=\frac{20.5}{20+5}=4\Omega\)
Có : R4nt(R1ntR2)//R3):
\(\Rightarrow\)Rtđ=R4+R123=6+4=10\(\Omega\)
\(\Rightarrow\)Ic=\(\frac{U}{R_{tđ}}=\frac{12}{10}=1,2A\)
\(\Rightarrow\)Ic=I4=I123=1,2A
\(\Rightarrow\)U4=I4.R4=1,2.6=7,2V
Có :R4nt((R1ntR2)//R3)
\(\Rightarrow\)U=U4+U123
\(\Rightarrow\)U123=U-U4=12-7,2=4,8V
mà (R1ntR2)//R3
\(\Rightarrow\)U12=U3=U123=4,8V
\(\Rightarrow\)I12=\(\frac{U_{12}}{R_{12}}=\frac{4,8}{20}=0,24A\)\(\Rightarrow\)I1=I2=I12=0,24A\(\Rightarrow\)\(\left\{{}\begin{matrix}U_1=R_1.I_1=10.0,24=2,4V\\U_2=R_2.I_2=10.0,24=2,4V\end{matrix}\right.\)
\(\Rightarrow\) I3=\(\frac{U_3}{R_3}=\frac{4,8}{5}=0,96\)A
\(=>R1nt\left(R2//R3\right)nt\left[R4//\left(R5ntR6\right)\right]\)
\(=>RTd=R1+\dfrac{R2R3}{R2+R3}+\dfrac{R4\left(R5+R6\right)}{R4+R5+R6}\)
\(=12,6+\dfrac{4.6}{4+6}+\dfrac{30\left(15+15\right)}{30+15+15}=30\left(om\right)\)
\(=>Im=\dfrac{U}{Rtd}=\dfrac{30}{30}=1A=I1=I23=I456\)
\(=>U23=I23.R23=1.\dfrac{4.6}{4+6}=2,4V=U2=U3\)
\(=>I2=\dfrac{U2}{R2}=\dfrac{2,4}{4}=0,6A=>I3=I23-I2=0,4A\)
\(=>U456=I456.R456=\dfrac{30\left(15+15\right)}{30+15+15}=15V=U4=U56\)
\(=>I4=\dfrac{U4}{R4}=\dfrac{15}{30}=0,5A\)
\(=>I56=I5=I6=\dfrac{U56}{R56}=\dfrac{15}{15+15}=0,5A\)
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