IGCSEPhysics: Co-ordinated Sciences (Double Award)CIERevision Notes3. WavesGeneral Properties of WavesThe Wave Equation

The Wave Equation (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Revision Note

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Ann H

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Physics

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The wave equation

The equation used to calculate wave speed is:

$v = f \times λ$

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

Wave speed is defined as:

The distance travelled by a wave each second

Wave speed is the speed at which energy is transferred through a medium
Transverse and longitudinal waves both obey the wave equation

Wave speed formula triangle

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

For more information on how to use a formula triangle refer to the revision note on speed & velocity

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: State the equation relating time period and frequency

$T = \frac{1}{f}$

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

$f = \frac{1}{T} = \frac{1}{2}$

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

$v = f \times λ$

Step 3: Rearrange the equation to calculate the wavelength

$λ = \frac{v}{f}$

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

$λ = \frac{0.15}{0.5}$

Wavelength, λ = 0.30 m

Exam 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 provide the speed in cm/s

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

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Author: Ann H

Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students no matter their schooling or background.