View attachment 168562
anh chin giúp em bài này với ạ, em cảm ơn
- Khi R = R1:
[tex]I1=\frac{E}{r+R1}[/tex]
[tex]P=I1^2.(r+R1)=\frac{E^2}{r+R1}=300=>E^2=300r+300R1[/tex] (1)
- Khi R=7/23R1:
[tex]I2=\frac{E}{r+\frac{7}{23}R1}=\frac{23E}{7R1+23r}[/tex]
[tex]I1+10=\frac{E}{r+R1}+10=\frac{E+10r+10R1}{r+R1}[/tex]
[tex]I2=I1+10=>\frac{23E}{7R1+23r}=\frac{E+10r+10R1}{r+R1}[/tex] (2)
- Khi R=11/23 R1:
[tex]I3=\frac{E}{r+\frac{11}{23}R1}=\frac{23E}{11R1+23r}[/tex]
[tex]2I1=\frac{2E}{r+R1}[/tex]
[tex]I3=2I1=>\frac{23E}{11R1+23r}=\frac{2E}{r+R1}=>23r+23R1=22R1+46r=>R1=23r[/tex] (3)
Thay (3) vào (2)
[tex]\frac{23E}{184r}=\frac{E+240r}{24r}=>552E=184E+44160r=>368E=44160r=>E=120r (4)[/tex]
Thay (3), (4) vào (1):
[tex]14400r^2=300r+6900r=>14400r^2-7200r=0=>\begin{bmatrix} r=0 (loại)& \\ r= 0,5 & \end{bmatrix}[/tex]
E=120r = 120.0,5= 60V
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