\(\def \u#1{\,\mathrm{#1}}\) \(\def \abs#1{\left|#1\right|}\) \(\def \ast{*}\) \(\def \deg{^{\circ}}\) \(\def \ten#1{\times 10^{#1}}\) \(\def \redcancel#1{{\color{red}\cancel{#1}}}\) \(\def \BLUE#1{{\color{blue} #1}}\) \(\def \RED#1{{\color{red} #1}}\) \(\def \PURPLE#1{{\color{purple} #1}}\) \(\def \th#1,#2{#1,\!#2}\) \(\def \lshift#1#2{\underset{\Leftarrow\atop{#2}}#1}}\) \(\def \rshift#1#2{\underset{\Rightarrow\atop{#2}}#1}}\) \(\def \dotspot{{\color{lightgray}{\circ}}}\)

Frequency

• A series of pulses which occur at regular intervals is called a wave. The time interval between pulses is called the period $T$ of the wave, and the frequency $f=1/T$ of the wave is the number of pulses that pass by per second.

The frequency of a wave has a second meaning, if we imagine the medium made up of a series of oscillators. Watch the red dot in this animation, which represents one such oscillator. Every time a pulse passes through it, the oscillator undergoes one complete cycle. Thus the frequency of the wave is also the frequency of the oscillators that make up the wave.

Pulses and waves can have many different shapes, but the ones we will study are sinusoidal waves, and appear as sines or cosines.