Câu trả lời:

r³ = \(\dfrac{2lkq^2}{mg}\) và r'³ = \(\dfrac{2lkq^2}{\varepsilon mg}\) \(\rightarrow\) \(\dfrac{r'^3}{r^3}\) = \(\dfrac{1}{\varepsilon}\) hay r' = \(\dfrac{r}{\sqrt[3]{\varepsilon}}\)