Đáp án:

 \(2\)

Giải thích các bước giải:

Ta có: 

\(\begin{array}{l}
\dfrac{{{P_1}}}{{{P_2}}} = \dfrac{{{{\left( {\dfrac{P}{{{U_1}}}} \right)}^2}{R_1}}}{{{{\left( {\dfrac{P}{{{U_2}}}} \right)}^2}{R_2}}} = {\left( {\dfrac{{{U_2}}}{{{U_1}}}} \right)^2}.\dfrac{{{R_1}}}{{{R_2}}} = {\left( {\dfrac{{{U_2}}}{{{U_1}}}} \right)^2}.\dfrac{{{l_1}}}{{{l_2}}}\\
 \Rightarrow \dfrac{{{P_1}}}{{{P_2}}} = {\left( {\dfrac{{200000}}{{100000}}} \right)^2}.\dfrac{{50}}{{100}} = 4.\dfrac{1}{2} = 2
\end{array}\)