pendulum, T \(\propto \sqrt{l}\)

\(5 \times {10^{ - 4}} = \frac{1}{2}\frac{{{r_1} - {r_2}}}{1}\)

\(\because\) change in length \(\Delta l=r_{1}-r_{2}\)

\(5 \times {10^{ - 4}} = \frac{1}{2}\frac{{{r_1} - {r_2}}}{1}\)

\(r_{1}-r_{2}=10 \times 10^{-4}\)

\(10^{-3} \mathrm{m}=10^{-1} \mathrm{cm}=0.1 \mathrm{cm}\)