Đáp án:
* K mở:
\[\begin{array}{l}
{U_r} = U - {U_1} = 22 - 21,2 = 0,8V\\
\Rightarrow \dfrac{r}{{{R_1}}} = \dfrac{{{U_r}}}{{{U_1}}} = \dfrac{{0,8}}{{21,2}} = \dfrac{2}{{53}}\\
\Rightarrow {R_1} = 26,5r
\end{array}\]
* K đóng:
\[\begin{array}{l}
{U_r} = U - {U_2} = 22 - 20 = 2V\\
\Rightarrow \dfrac{r}{{\dfrac{{{R_1}{R_2}}}{{{R_1} + {R_2}}}}} = \dfrac{{{U_r}}}{{{U_2}}} = \dfrac{2}{{20}} = \dfrac{1}{{10}}\\
\Rightarrow \dfrac{r}{{\dfrac{{26,5r.{R_2}}}{{26,5r + {R_2}}}}} = \dfrac{1}{{10}}\\
\Rightarrow \dfrac{{26,5r.{R_2}}}{{26,5r + {R_2}}} = 10r\\
\Rightarrow {R_2} = \dfrac{{53}}{{33}}r
\end{array}\]
Suy ra:
\[\begin{array}{l}
{R_2} = \dfrac{2}{{33}}{R_1}\\
\Rightarrow {P_2} = \dfrac{{33}}{2}{P_1} = 165W
\end{array}\]
