a
\(r\,\, = \,\,\frac{{\sqrt {{Q_1}} }}{{\sqrt {{Q_1}\,\, - \,\,{Q_2}} }}\,\,x\,\, \Rightarrow \,\,\frac{{\sqrt {8q} }}{{\sqrt {8q} \, - \,\,\sqrt {2q} }}\,\,.\,\,L\)
\(r\,\, = \,\,\frac{{2\,\sqrt {2q} }}{{2\sqrt {2q} \,\, - \,\,\sqrt {2q} }}\,\,L\,\, \Rightarrow \,\,r\,\, = \,\,2L\)