c3: R2 nt( R1//Rv)
a,\(\Rightarrow U1=Uv=60V\Rightarrow I1=\dfrac{60}{R1}=\dfrac{60}{2000}=\dfrac{3}{100}A\)
\(\Rightarrow U2=U-U1=180-60=120V\Leftrightarrow I2=\dfrac{U2}{R2}=\dfrac{120}{3000}=0,04A\)
b, khi mach von ke song song vs R2
do von ke mang dien tro Rv(khong ly tuong)ne coi von ke la 1 dien tro
=>(R2//Rv)nt R1
\(\Rightarrow Iv=I2-I1=0,04-\dfrac{3}{100}=0,01A\)
\(\Rightarrow Rv=\dfrac{U1}{Iv}=\dfrac{60}{0,01}=6000\Omega\)
\(\Rightarrow Uv=Im.\left(\dfrac{R2.Rv}{R2+Rv}\right)=\left(\dfrac{180}{R1+\dfrac{R2Rv}{R2+Rv}}\right)\left(\dfrac{R2.Rv}{R2+Rv}\right)=90V\)
c4:
a, von ke chi 0V=>(R1 nt R2)//(R3 nt R4)
\(Uv=0\Rightarrow-U1+U3=0\Leftrightarrow U3=U1\)
\(\Rightarrow I34.R3=I12.R1\)
\(\Rightarrow\dfrac{U34}{R3+R4}.R3=\dfrac{U12}{R1+R2}.R1\Leftrightarrow\dfrac{20R3}{20+R3}=\dfrac{40}{10}\Rightarrow R3=5\Omega\)
b, von ke chi 4V \(\Rightarrow4=-U1+U3\)
\(\Rightarrow U3=4+U1\Rightarrow\dfrac{20R3}{20+R3}=4+\dfrac{40}{10}\Rightarrow R3=13,333\Omega\)
