# University of Auckland/Department of Physics/Physics 102/Description of Waves

## Wave defined

A wave can be described as a repeating disturbance that travels through a medium (e.g. air) from one location to another with no net transfer of matter. However, energy is transferred.

## Crest and Trough

The crest of a wave is the top of the wave and the trough of a wave is the bottom of the wave. File:CrestAndTrough.gif

## Period

Period
 The length of time for one cycle of the wave (i.e. the length of time between two consecutive crests or two consecutive troughs).

## Wavelength

Wavelength
 The distance between two consecutive crests or troughs. Wavelength.gif Wavelength 2.gif The units of wavelength are m, km, μm, nm, etc

## Wave Speed

Wave Speed
 $v = {\lambda}{f} = \frac{\lambda}{T}$ It has units of m/s, km/s, mm/s, etc

The wave speed doesn't change if you change the wave length, frequency or period for a wave for a given material. This is because if one of the variables (λ, f, T) is changed, the others also change so that the velocity is the same e.g.

• if the frequency is halved, the wavelength is doubled and the period is doubled
• if the frequency is tripled, the wavelength and period and a third of their value

Speed of sound in air = 340 ms-1

Speed of light in air = 3 x 108 m s-1

-Wave velocity is related to frequency and wavelength. We can show a series of wave pulses by hitting the surface of the water in a pool many times.The pulse will move some distance before the second pulse from the original hitting site.That is referred to as the wavelength. -The distance between pulses is λ(Greek for Lambda), and the time between pulses is the period,(T), and the speed of the wave is the distance divided by the time, v = λ/T.

Calculating wave speed : Wave Speed=wavelength * frequency

Frequency=1/period Since the frequency and period are the inverse of each other, therefore, Period=1/Frequency. http://www.brainpop.com/

## Amplitude

The amplitude is the maximum displacement of the wave.

## FYI

Heres a link thats like an online interactive textbook. Will answer any questions you might have..: http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/wavestoc.html (dhic014)