IGCSEPhysicsCambridge (CIE)Revision Notes3. WavesGeneral Properties of WavesThe Wave Equation

The Wave Equation (Cambridge (CIE) IGCSE Physics)

Revision Note

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Katie M

Written by: Katie M

Reviewed by: Caroline Carroll

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The wave equation

  • The equation used to calculate wave speed is: 

v space equals space f space cross times space lambda

  • 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 space equals space 1 over f

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

f space equals space 1 over T space equals space 1 half

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 space equals space f space cross times space lambda

Step 3: Rearrange the equation to calculate the wavelength

lambda space equals space v over f

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

lambda space equals space fraction numerator 0.15 over denominator 0.5 end fraction

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 provide the speed in cm/s

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

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    Katie M

    Author: Katie M

    Expertise: Physics

    Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

    Caroline Carroll

    Author: Caroline Carroll

    Expertise: Physics Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.