The Wave Equation (AQA GCSE Combined Science: Trilogy): Revision Note
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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:
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:
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
Answer:
Part (a)
Step 1: List the known quantities
Time period, T = 2 s
Step 2: Write out the equation relating time period and frequency
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 Tips and Tricks
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
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