The Wave Equation (Edexcel International A Level Physics)

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Lindsay Gilmour



The Wave Equation

The Wave Equation

  • This equation links wave speed, frequency and wavelength

Wave equation, downloadable AS & A Level Physics revision notes

  • Where:
    • v = velocity of the wave (m s–1)
    • f = frequency of the wave (Hz)
    • λ = wavelength (m)

  • The wave equation tells us that for a wave of constant speed:
    • As the wavelength increases, the frequency decreases
    • As the wavelength decreases, the frequency increases

 Frequency and wavelength, downloadable AS & A Level Physics revision notes

The relationship between frequency and wavelength of a wave

Worked example

A travelling wave has a period of 1.0 μs and travels at a velocity of 100 cm s–1. Calculate the wavelength of the wave. Give your answer in metres (m).

Step 1: Write down the known quantities

    • Period, T = 1.0 μs = 1.0 × 10–6 s
    • Velocity, c = 100 cm s–1 = 1.0 m s–1

Note the conversions:

    • The period must be converted from microseconds (μs) into seconds (s)
    • The velocity must be converted from cm s–1 into m s–1

Step 2: Write down the relationship between the frequency f and the period T 

1 over T

Step 3: Substitute the value of the period into the above equation to calculate the frequency 

fraction numerator 1 over denominator 1 cross times 10 to the power of negative 6 end exponent end fraction

f = 1.0 × 106 Hz

Step 4: Write down the wave equation

c = fλ

Step 5: Rearrange the wave equation to calculate the wavelength λ

λ c over f

Step 6: Substitute the numbers into the above equation 

λ fraction numerator 1.0 over denominator 1 cross times 10 to the power of 6 end fraction

λ = 1 × 10–6 m

Exam Tip

This is an important equation that comes up in many other topics. Get really familiar with using it and rearranging it. 

Be ready to use prefixes with values, for example, nanometres (nm = m × 10−9) or MHz (MHz = Hz × 106).

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.

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