Đáp án:
B.\(\dfrac{{{L_1}}}{{{L_2}}} = \dfrac{1}{2}\)
Giải thích các bước giải:
Ta có:
\[L = 4\pi {.10^{ - 7}}\frac{{{N^2}}}{l}S\]
Vậy \(\dfrac{{{L_1}}}{{{L_2}}} = \dfrac{{{N_1}^2}}{{{N_2}^2}}.\dfrac{{{l_2}}}{{{l_1}}} = \dfrac{{{N_1}^2}}{{4{N_1}^2}}.\dfrac{{2{l_1}}}{{{l_1}}} = \dfrac{1}{2}\)