Wave Vocabulary

Webster's dictionary defines a wave as "a disturbance or variation that transfers energy progressively from point to point in a medium and that may take the form of an elastic deformation or of a variation of pressure, electric or magnetic intensity, electric potential, or temperature."

The most important part of this definition is that a wave is a disturbance or variation which travels through a medium. The medium through which the wave travels may experience some local oscillations as the wave passes, but the particles in the medium to not travel with the wave. The disturbance may take any of a number of shapes, from a finite width pulse to an infinitely long sine wave.

Definition Provided by Dr Dan Russel

Frequency:   Frequency refers to how many waves are made per time interval. This is usually described as how many waves are made per second, or as cycles per second.

Hertz is a unit of frequency (of change in state or cycle in a sound wave, alternating current, or other cyclical waveform) of one cycle per second. It replaces the earlier term of "cycle per second (cps)." Even though a Hertz is a per second, which would seem to me to be a base unit (because a second is a base unit).  It's not considered a base unit because a hertz is CYCLE / SECONDS which means in order to "measure" a hertz you would need to count (measure) the number of cycles and and time,  and thats why it's not a base unit Example:  Three waves are plotted for one second in the diagram above, each wave has a different frequency.

The upper most plot shows a wave with a frequency of 20 Hz, It completes 20 full cycles in one second, 20 cycles / 1 sec = 20 Hz

The middle plot shows a wave with a frequency of 40 Hz, it completes 40 full cycles in one second, 40 cycles / 1 sec = 40 Hz

The bottom plot shows a wave of 80 Hz.

Period:   Period refers to the time which it takes to do something. When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period.

The Frequency Period Connection. Frequency is offend refereed to as the number of events that happens in a given time. Frequency simplified is simple cycles / Sec.  Period on the other hand is the amount of time it takes for a single event.  Period simplified is sec / cycle.

So the relationship between them is Frequency = 1 / Period Example:  Three waves are plotted for one second in the diagram above, each wave has a different frequency.

The upper most plot shows a wave with a frequency of 20 Hz, It completes 20 full cycles in one second, 20 cycles / 1 sec = 20 Hz. The period is 1/20 sec, It takes 1/20 th of a second for that event to happen again

The middle plot shows a wave with a frequency of 40 Hz, it completes 40 full cycles in one second, 40 cycles / 1 sec = 40 Hz.  The period is 1/40 sec, it takes only 1/40 th of a second for that event to happen again

The bottom plot shows a wave of 80 Hz. The period is 1/80 sec.

Crest and Trough:  The section of the wave that rises above the undisturbed position is called the crest. That section which lies below the undisturbed position is called the trough. These sections are labeled in the diagram below: Wavelength:  The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train. This distance is usually measured in one of three ways:  Crest to the next cresttrough to next trough, or from the start of a wave cycle to the next starting point. This is shown in the following diagram: Equilibrium:  In the diagram below the white line represents the position of the medium when no wave is present. This medium could be imagined as a rope fixed at one end a few feet above the ground and held by you at the other end.

The yellow line represents the position of the medium as a wave travels through it. We simply say that the yellow line is the wave. If we consider the rope mentioned before, this wave could be created by vertically shaking the end of the rope. Amplitude:  The term amplitude can have slightly different meanings depending upon the context of the situation.

Its most general definition is that the amplitude is the maximum positive displacement from the undisturbed position of the medium to the top of a crest. In some discussions it is important to distinguish between positive and negative amplitudes. These displacements are shown in the following diagram: The hidden relationship between velocity, frequency and wavelength 