Transverse and longitudinal waves

    AQA
    GCSE

    Waves transfer energy and information without the net transfer of matter. Transverse waves feature oscillations perpendicular to the direction of energy propagation, exemplified by electromagnetic radiation and seismic S-waves. Longitudinal waves involve oscillations parallel to energy propagation, forming regions of compression and rarefaction, characteristic of sound waves and seismic P-waves. Candidates must analyze these motions using wavefront diagrams and apply the wave equation to calculate velocity, frequency, and wavelength.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating transverse wave oscillations are perpendicular (at 90 degrees) to the direction of energy transfer
    • Award 1 mark for stating longitudinal wave oscillations are parallel to the direction of energy transfer
    • Credit responses that identify regions of high density as 'compressions' and low density as 'rarefactions' in longitudinal waves
    • Award 1 mark for evidence that the medium does not travel, e.g., a cork bobbing up and down as a water wave passes
    • For calculations, award marks for correct substitution into v = f λ even if the final answer is incorrect

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating transverse wave oscillations are perpendicular (at 90 degrees) to the direction of energy transfer
    • Award 1 mark for stating longitudinal wave oscillations are parallel to the direction of energy transfer
    • Credit responses that identify regions of high density as 'compressions' and low density as 'rarefactions' in longitudinal waves
    • Award 1 mark for evidence that the medium does not travel, e.g., a cork bobbing up and down as a water wave passes
    • For calculations, award marks for correct substitution into v = f λ even if the final answer is incorrect

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Memorise the specific phrase 'oscillations are perpendicular to the direction of energy transfer'—imprecise phrasing like 'moves at right angles' often loses marks
    • 💡When calculating wave speed, always check the units of wavelength; if given in cm, divide by 100 to get metres immediately
    • 💡In 6-mark questions describing the Ripple Tank practical, explicitly state how you measure wavelength (e.g., 'measure 10 waves and divide by 10') to improve accuracy
    • 💡Remember: Sound waves and P-waves are longitudinal; Electromagnetic waves, S-waves, and water ripples are transverse

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Describing oscillations as 'perpendicular to the wave' rather than 'perpendicular to the direction of energy transfer'
    • Failing to convert wavelengths from cm or mm into metres before substituting into the wave speed equation
    • Confusing amplitude with the peak-to-peak distance; amplitude is the maximum displacement from the equilibrium position
    • Stating that water or air particles move from the source to the detector, rather than oscillating about a fixed point

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    State
    Describe
    Explain
    Calculate
    Compare

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 8","title":"Ripple Tank and String","relevance":"Measuring frequency, wavelength, and speed of transverse waves"}

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