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

## Contents

## 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

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

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

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 10^{8} 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.
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## Amplitude

The amplitude is the maximum displacement of the wave.

- Amplitude1.gif
- Calculating Wavelength of radio waves.
- The speed of light is 3.0 X 10^8 m/s. What is the wavelength of
- The radio waves emitted by KKJZ, a station whose frequency is 88.1 MHz? Solving for wavelength, we have
- Amplitude2.gif

## Wave on a string example

## External Resources

## 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)

Here is a link with practice questions for wavelenght http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Vibrations%20and%20Waves/Progressive%20waves/file_4219.doc (Jshe128)

(asch115):This is a really basic sight on waves; its basically waves for Dummies, but it gives good interactive examples to help you visualize the basic components of waves:

http://sunshine.chpc.utah.edu/labs/waves/wave_basics/waves.htm