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GCSEPhysicsEdexcelRevision Notes4. WavesProperties of WavesThe Wave Equation

The Wave Equation (Edexcel GCSE Physics)

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The Wave Equation

  • Wave speed is defined as:

The distance travelled by a wave each second

  • The wave speed can be calculated in a similar way to calculating the speed of moving objects:

wave space speed space equals space distance over time

v space equals space x over t

  • Where:

    • v = wave speed in metres per second (m/s)

    • x = distance travelled by the wave in metres (m)

    • t = time taken in seconds (s)

  • All waves obey the wave equation, which is another way to calculate the wave speed:

wave space speed space equals space frequency space cross times space wavelength

v space equals space f space cross times space lambda

  • 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

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

T space equals space 1 over f

Step 3: Rearrange for frequency f and calculate the answer

space 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 for wavelength λ and calculate the answer

lambda space equals space v over f 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 give the speed in cm/s

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

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    Ashika

    Author: Ashika

    Expertise: Physics Project Lead

    Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.