In an experiment to determine the period of a simple pendulum of length 1 m, it is attached to different spherical bobs of radii $r _ { 1 }$ and $r _ { 2 }$. The two spherical bobs have uniform mass distribution. If the relative difference in the periods, is found to be $5 \times 10 ^ { - 4 } \mathrm {~s}$, the difference in radii, $\left| r _ { 1 } - r _ { 2 } \right|$ is best-given by\\
(1) 0.01 cm\\
(2) 0.05 cm\\
(3) 0.5 cm\\
(4) 1 cm