Define periodic time and frequency,their units,and the relationship between them.

(N/A) $1$. Periodic Time $(T)$: It is defined as the time taken by an oscillating particle to complete one full oscillation. Its $SI$ unit is second $(s)$.
$2$. Frequency ($f$ or $\nu$): It is defined as the number of oscillations completed by a particle in one second. Its $SI$ unit is Hertz $(Hz)$,where $1 \ Hz = 1 \ s^{-1}$.
$3$. Relationship: The frequency is the reciprocal of the periodic time. Mathematically,$f = \frac{1}{T}$ or $T = \frac{1}{f}$.