解:電流表?$A_2$?測量?$R_1$?的電流?$I_{1 }=\frac {U_{ }}{2\ \mathrm {Ω}}$?
?$ $?數(shù)據(jù)只能取?$U=2\ \text {V}$?,?$I_1=1\ \text {A}$?,所以?$A_1$?的示數(shù)?$I=3\ \text {A}$?
?$ $?電源電壓?$U=2\ \text {V}$?
?$ I_2=I-I-1=3\ \text {A}-1\ \text {A}=2\ \text {A}$?
?$ R_{2 }=\frac {U_{ }}{I_{ 2 }}=\frac {{ 2 }\ \text {V}}{{ 2 }\ \text {A}}={ 1 }Ω$?