Câu hỏi 29

Ta có: \(\left\{ \begin{array}{l}{n_1} = {k_1} + 1 = 16 \Rightarrow {k_1} = 15\\{n_2} = {k_2} + 1 = 10 \Rightarrow {k_2} = 9\end{array} \right.\)

Lại có:

\(\begin{array}{l}\left\{ \begin{array}{l}l = \dfrac{{{k_1}.v}}{{2{f_1}}}\\l = \dfrac{{{k_2}.v}}{{2{f_2}}}\end{array} \right. \Rightarrow \dfrac{{{k_1}.v}}{{2{f_1}}} = \dfrac{{{k_2}.v}}{{2{f_2}}} \Leftrightarrow \dfrac{{{k_1}}}{{{f_1}}} = \dfrac{{{k_2}}}{{{f_2}}}\\ \Rightarrow {f_2} = \dfrac{{{k_2}{f_1}}}{{{k_1}}} = \dfrac{{9.50}}{{15}} = 30Hz\end{array}\)

Chọn C.