The Wave Equation

Wave speed is defined as:

The distance travelled by a wave each second

Wave speed is given the symbol ν and is measured in metres per second (m/s)
Wave speed is the speed at which energy is transferred through a medium
Transverse and longitudinal waves both obey the wave equation:

Wave equation, IGCSE & GCSE Physics revision notes

Where:
- v = wave speed in metres per second (m/s)
- f = frequency in Hertz (Hz)
- λ = wavelength in metres (m)

The wave speed equation may need to be rearranged, which can be done using this formula triangle:

Wave speed triangle (2), IGCSE & GCSE Physics revision notes

Worked example

A wave in a pond has a speed of 0.15 m/s and a time period of 2 seconds.Calculate:

a) The frequency of the wave

b) The wavelength of the wave

Part (a)

Step 1: List the known quantities

- Time period, T = 2 s

Step 2: Write out the equation relating time period and frequency

Time Period Equation

Step 3: Rearrange for frequency, f, and calculate the answer

f = 1 ÷ T = 1 ÷ 2

Frequency, f = 0.5 Hz

Part (b)

Step 1: List the known quantities

- Wave speed, v = 0.15 m/s
- Frequency, f = 0.5 Hz

Step 2: Write out the wave speed equation

v = f × λ

Step 3: Rearrange the equation to calculate the wavelength

λ = v ÷ f

Step 4: Use the frequency you calculated in part (a) and put the values into the equation

λ = 0.15 ÷ 0.5

Wavelength, λ = 0.30 m

Examiner Tip

When stating equations make sure you use the right letters:

For example, use λ for wavelength, not L or W

If you can’t remember the correct letters, then just state the word equations

Be careful with units: wavelength is usually measured in metres and speed in m/s, but if the wavelength is given in cm you might have to give the speed in cm/s

Likewise, watch out for frequency given in kHz: 1 kHz = 1000 Hz

The Wave Equation (AQA GCSE Physics: Combined Science)

Revision Note