\(l \propto \frac{L}{{{r^2}}}\) \((Y\) and \(F\) are constant\()\)
\(\frac{{{l_2}}}{{{l_1}}} = \frac{{{L_2}}}{{{L_1}}} \times {\left( {\frac{{{r_1}}}{{{r_2}}}} \right)^2} = (2) \times {\left( {\frac{1}{2}} \right)^2} = \frac{1}{2}\) ==> \({l_2} = \frac{{{l_1}}}{2} = \frac{{0.01m}}{2} = 0.005m\)