Period and frequency
Two more quantities describe how fast the particles oscillate: how long one oscillation takes, and how many happen every second.
Period (T)
The time a particle takes to make one complete oscillation is called the period (T).
The time a wave takes to travel a distance equal to one wavelength is also equal to the period.
Frequency (f)
The number of oscillations a particle makes in unit time is called the frequency (f). Its unit is the hertz (Hz): one hertz is one oscillation per second.
Frequency and period
f = 1 / T
frequency is the reciprocal of the period
An example
Problem
A metal strip makes 50 vibrations in 5 seconds. Find its frequency and its period.
Solution
frequency = number of vibrations ÷ time = 50 ÷ 5 s
= 10 Hz
period T = 1 ÷ f = 1 ÷ 10 Hz
= 0.1 s