সরল দোলকের দোলনকাল = ?

$\mathrm{T}=2 \pi \sqrt{\frac{\ell}{\mathrm{g}}}$

$\mathrm{T}=2 \pi \mathrm{r} \sqrt{\frac{\ell}{\mathrm{g}}}$

$\mathrm{T}=2 \pi^{2} \mathrm{r}^{2} \sqrt{\frac{\ell}{\mathrm{g}}}$

$T=2 \pi^{2} \sqrt{\frac{\ell}{g}}$