Wave Motion (Oxford AQA IGCSE Combined Science Double Award)

Wave Motion

• When describing wave motion, there are several terms which are important to know, including:

  • Amplitude ()

  • Wavelength ()

  • Frequency ()

  • Wave speed () 

Amplitude

• Amplitude is defined as:

The distance from the undisturbed position to the peak (crest) or trough of a wave

• It is given the symbol and is measured in metres (m)

• Amplitude is the maximum or minimum displacement from the undisturbed position

Wavelength

• Wavelength is defined as

The distance from one point on the wave to the same point on the next wave

• In a transverse wave:

  • The wavelength can be measured from one peak to the next peak

• In a longitudinal wave:

  • The wavelength can be measured from the centre of one compression to the centre of the next

• The wavelength is given the symbol  (lambda) and is measured in metres (m)

Graphical representation of transverse waves

• The amplitude and wavelength of a transverse wave can be represented graphically

• The distance along a wave is typically put on the x-axis of a wave diagram

A diagram of a transverse wave

Frequency

• Frequency is defined as:

The number of waves passing a point in a second

• Frequency is given the symbol and is measured in hertz (Hz)

  • The unit hertz is equivalent to 'per second'

  • 5 Hz = 5 waves per second

Time Period

• The time period (or sometimes just 'period') of a wave is defined as:

The time taken for a single wave to pass a point

• The time period can be calculated using:

• Where:

  • T = time period measured in seconds (s)

  • f = frequency measured in hertz (Hz)

Wavefront

• Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave

• The image below illustrates how wavefronts are visualised:

  • The arrow shows the direction the wave is moving and is sometimes called a ray

  • The space between each wavefront represents the wavelength

  • When the wavefronts are close together, this represents a wave with a short wavelength

  • When the wavefronts are far apart, this represents a wave with a long wavelength

A series of wavefronts

Wave speed

• Wave speed is the speed at which energy is transferred through a medium

• Wave speed is defined as:

The distance travelled by a wave each second

• Wave speed is given the symbol  and is measured in metres per second (m/s),