Đáp án:

 \(\dfrac{{{\varepsilon _1}}}{{{\varepsilon _2}}} = 0,25\)

Giải thích các bước giải:

Ta có: 

\(\begin{array}{l}
\dfrac{{{F_1}}}{{{F_2}}} = \dfrac{{\dfrac{{k.\left| {{q_1}{q_2}} \right|}}{{{\varepsilon _1}r_1^2}}}}{{\dfrac{{k.\left| {{q_1}{q_2}} \right|}}{{{\varepsilon _2}r_2^2}}}} = \dfrac{{{\varepsilon _2}}}{{{\varepsilon _1}}}.{\left( {\dfrac{{{r_2}}}{{{r_1}}}} \right)^2}\\
 \Rightarrow 1 = \dfrac{{{\varepsilon _2}}}{{{\varepsilon _1}}}.{\left( {\dfrac{1}{2}} \right)^2}\\
 \Rightarrow \dfrac{{{\varepsilon _1}}}{{{\varepsilon _2}}} = 0,25
\end{array}\)