a
(a) Wave number = \(\frac{1}{\lambda }\) but \(\frac{1}{{\lambda '}} = \frac{1}{\lambda }\left( {\frac{v}{{v - {v_s}}}} \right)\,{\rm{and}}\;{v_s} = \frac{v}{3}\)
\(\therefore \) \((W.N.)’ = (W.N.)\) \(\left( {\frac{v}{{v - v/3}}} \right) = 256 \times \frac{v}{{2v/3}}\)
= \(\frac{3}{2} \times 256 = 384\)