Giúp mình bài này đi các bạn :
View attachment 125944
Ta có: [tex]C_{1234}=\frac{C_{1}C_{2}}{C_{1}+C_{2}}+\frac{C_{3}C_{4}}{C_{3}+C_{4}}[/tex][tex]=4.10^{-6}[/tex](F)
[tex]\Rightarrow C=\frac{C_{1234}.C_{5}}{C_{1234}+C_{5}}=\frac{8}{3}.10^{-6}[/tex] (F)
[tex]\Rightarrow Q_{5}=Q=UC=2,4.10^{Ơ-3}(C)[/tex]
[tex]\Rightarrow U_{5}=\frac{Q_{5}}{C_{5}}=300(V)[/tex]
[tex]\Rightarrow U_{1234}=U-U_{5}=600(V)[/tex]
Có: [tex]U_{1}+U_{2}=U_{1234}=600(V)[/tex]
[tex]\Rightarrow Q_{1}=Q_{12}=U_{12}.C_{12}=1,2.10^{Ơ-3}(C)[/tex]
[tex]\Rightarrow U_{1}=\frac{Q_{1}}{C_{1}}=400(V)[/tex]
Lại có: [tex]U_{3}+U_{4}=U_{1234}=600(V)[/tex]
Tương tự ta được [tex]U_{3}=300(V)[/tex]
Mặt khác: [tex]U_{AB}=-U_{1}+U_{3}[/tex]=-400+300=-100(V)