Sound Waves

    OCR
    GCSE

    Sound waves are longitudinal mechanical waves requiring a medium for propagation, characterized by regions of compression and rarefaction where particle oscillation is parallel to the direction of energy transfer. Analysis involves the quantitative relationships between wave speed, frequency, and wavelength, alongside the qualitative correlation of amplitude with loudness and frequency with pitch. Advanced study encompasses the reflection, refraction, and absorption of sound at boundaries, extending to the applications of ultrasound in medical imaging and industrial depth detection (sonar).

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    Objectives
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    Exam Tips
    4
    Pitfalls
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    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for defining sound as a longitudinal wave where particle oscillation is parallel to the direction of energy transfer
    • Credit responses that identify compressions as regions of high pressure/density and rarefactions as regions of low pressure/density
    • In echo calculations, award 1 mark for explicitly using distance = speed × (time / 2) or 2 × distance = speed × time
    • Award 1 mark for stating that ultrasound consists of sound waves with frequencies above the upper limit of human hearing (20,000 Hz)
    • For ultrasound imaging, credit the explanation that partial reflection occurs at the boundary between two different media

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated the speed, but check your significant figures—does your answer match the precision of the data given?"
    • "Good definition of a longitudinal wave. To secure the mark, explicitly state the relationship between oscillation direction and energy transfer"
    • "You missed the 'echo' factor here. Remember, the sound travels to the object and back, so the distance is doubled"
    • "Excellent explanation of ultrasound. For the top band, mention that reflection happens specifically at the boundary between media of different densities"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining sound as a longitudinal wave where particle oscillation is parallel to the direction of energy transfer
    • Credit responses that identify compressions as regions of high pressure/density and rarefactions as regions of low pressure/density
    • In echo calculations, award 1 mark for explicitly using distance = speed × (time / 2) or 2 × distance = speed × time
    • Award 1 mark for stating that ultrasound consists of sound waves with frequencies above the upper limit of human hearing (20,000 Hz)
    • For ultrasound imaging, credit the explanation that partial reflection occurs at the boundary between two different media

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always highlight whether the time given in a question is for a one-way trip or a return journey (echo); this is the most frequent calculation trap
    • 💡When describing longitudinal waves, use the terms 'compression' and 'rarefaction' rather than 'peaks' and 'troughs', which apply to transverse waves
    • 💡For Higher Tier questions on ultrasound, focus on the mechanism: the pulse is emitted, reflects at a boundary, and the time delay is used to calculate distance

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing the motion of particles with the motion of the wave; students often incorrectly suggest air particles travel from source to receiver
    • Neglecting to halve the time or double the distance in sonar/echo questions, leading to incorrect numerical answers
    • Confusing amplitude with frequency when describing changes in loudness (amplitude) versus pitch (frequency)
    • Failing to convert units, such as leaving frequency in kHz when the speed is in m/s

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Longitudinal wave mechanics (compression/rarefaction)
    Wave equation application (v = fλ)
    Reflection (echoes) and absorption
    Ultrasound principles and applications
    Human hearing range and ear mechanics

    Likely Command Words

    How questions on this topic are typically asked

    State
    Calculate
    Explain
    Describe
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"PAG P8","title":"Measuring the speed of waves","relevance":"Methods to measure speed of sound in air using echoes or microphones"}

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