\(R_1=\dfrac{U^2_{dm1}}{P_{dm1}}=\dfrac{120^2}{60}=240\left(\Omega\right);R_2=\dfrac{U_{dm2}^2}{P_{dm2}}=\dfrac{120^2}{40}=360\left(\Omega\right)\)
\(R_1ntR_2\Rightarrow R_{12}=R_1+R_2=240+360=600\left(\Omega\right)\)
\(\Rightarrow I=\dfrac{U}{R_{12}}=\dfrac{U}{R_1+R_2}=\dfrac{240}{600}=0,4\left(A\right)\)
\(I_{dm1}=\dfrac{P_{dm1}}{U_{dm1}}=\dfrac{60}{120}=\dfrac{1}{2}\left(A\right);I_{dm2}=\dfrac{P_{dm2}}{U_{dm2}}=\dfrac{40}{120}=\dfrac{1}{3}\left(A\right)\)
\(I_{dm1}>I\Rightarrow den-1-sang-hon-binh-thuong\)
\(I_{dm2}< I\Rightarrow den-2-sang-yeu-hon-binh-thuong\)
Thấy Idm1 >Idm2=> Ta sẽ mắc như vầy: \(R_1nt\left(R_2//R_b\right)\Rightarrow R_{td}=R_1+\dfrac{R_2.R_b}{R_2+R_b}\)
\(\Rightarrow I_1=\dfrac{1}{2}\left(A\right);I_2=\dfrac{1}{3}\left(A\right)\)
\(\Rightarrow I_b=I_1-I_2=\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{1}{6}\left(A\right)\)
\(\Rightarrow U_b=U-U_1=240-I_1.R_1=240-\dfrac{1}{2}.240=120\left(V\right)\)
\(\Rightarrow R_b=\dfrac{U_b}{I_b}=\dfrac{120}{\dfrac{1}{6}}=720\left(\Omega\right)\)
