\( = \,\,Q\,\,\left[ {{V_D}\,\, - \,\,{V_C}} \right]\,\because \,\,{V_D}\,\, = \,\,\frac{{kq}}{{3L}}\,\, - \,\,\frac{{kq}}{L}\,\, = \,\,\frac{{ - 2}}{3}\,\,\frac{{kq}}{L}\)

\({V_c}\,\, = \,\,\frac{{kq}}{L}\,\, - \,\,\frac{{kq}}{L}\,\, = \,\,0\)

\(\therefore \,\,W\,\, = \,\,Q\,\,\left[ { - \frac{2}{3}\,\,\frac{{kq}}{L}\,\, - \,\,0} \right]\,\, = \,\, - \frac{2}{3}\,\,\frac{{kqQ}}{L}\,\, = \,\, - \,\,\frac{{qQ}}{{6\pi { \in _0}L}}\)