end, \({n_c} = \frac{{3v}}{{4{l_c}}}\).....\((i)\)
Third harmonic or second overtone of organ pipe open at both end,
\({n_0} = \frac{{3v}}{{2{l_0}}}\).....\((ii)\)
given \({n_c} = {n_o}\)
\( \Rightarrow \,\,\,\,\frac{{3v}}{{4{l_c}}} = \frac{{3{v_0}}}{{2{l_0}}}\,\,\,\)
\(\Rightarrow \,\,\frac{{{l_c}}}{{{l_o}}} = \frac{1}{2}.\)