Describing Wave Motion (AQA GCSE Combined Science: Trilogy): Revision Note

Describing Wave Motion

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

  • amplitude

  • wavelength

  • frequency

  • period

Amplitude

• Amplitude is defined as:

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

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

• On a graph where the vertical axis is displacement, 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 (lambda) and is measured in metres (m)

• On a graph where the horizontal axis is distance, the wavelength can be determined by measuring the distance from one point on the wave to the same point on the next wave

Using a graph to determine wavelength and amplitude

Diagram showing the amplitude and wavelength of a 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

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

Time period

• The time period of a wave is defined as:

The time taken for a single wave to pass a point

• This can also be stated as:

The time taken for one full cycle of a wave

• Time period is given the symbol and is measured in seconds (s)

• The frequency and period of a wave are related by the equation:

• Where:

  • = frequency of the wave, measured in hertz (Hz)

  • = period of the wave, measured in seconds (s)

• On a graph where the horizontal axis is time, the period can be determined by measuring the time from one point on the wave to the same point on the next wave

Using a graph to determine time period

Diagram showing the time period of a wave