Moment of inertia of a cylinder of mass m, length L and radius R about an axis passing through its centre and perpendicular to the axis of the cylinder is $I = M \left( \frac { R ^ { 2 } } { 4 } + \frac { L ^ { 2 } } { 12 } \right)$. If such a cylinder is to be made for a given mass of a material, the ratio $\frac { L } { R }$ for it to have minimum possible $I$ is:
(1) $\frac { 2 } { 3 }$\\
(2) $\frac { 3 } { 2 }$\\
(3) $\sqrt { \frac { 3 } { 2 } }$\\
(4) $\sqrt { \frac { 2 } { 3 } }$