Describing Wave Motion (Edexcel IGCSE Physics): Revision Note

Describing wave motion

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

  • Wavefront

  • Amplitude (A)

  • Wavelength (λ)

  • Frequency (f)

  • Time Period (T)

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

Wavefronts viewed from above

Diagram showing a wave moving to the right, drawn as a series of wavefronts

Amplitude

• Amplitude is defined as:

The maximum displacement of a wave from its undisturbed position

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

• Amplitude is measured from the undisturbed position to either the highest point of the wave (peak) or the lowest point (trough)

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

• Wavelength is given the symbol λ (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

Diagram showing the amplitude and wavelength of a transverse wave

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

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

Frequency

• Frequency is defined as:

The number of waves passing a point in a second

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

  • The unit hertz is equivalent to 'per second'

  • 5 Hz = 5 waves per second

• Waves with a higher frequency transfer a higher amount of energy

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 period  is measured in seconds (s)

• The equation linking frequency and time period is explained in Frequency & time period