Theo hình :
R1 nt R2 nt R3
=> \(U_{12}=U_1+U_2=10\left(V\right)\)
\(U_{23}=U_2+U_3=12V\)
\(=>U_{23}-U_{12}=U_2+U_3-U_1-U_2=U_3-U_1=12-10=2\left(V\right)\left(1\right)\)
Mà :
\(I=I_1=I_2=I_3\)
\(R_3=2R_1\)
\(=>I.R_3=I.2R_1\)
\(=>U_3=2U_1\left(2\right)\)
giải hệ (1) và (2) có :
\(U_3=4\left(V\right);U_1=2\left(V\right)\)
\(=>U_2=8\left(V\right)\)
\(=>U_{AB}=U_1+U_2+U_3=2+8+4=14\left(V\right)\)
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