Wave Speed

    OCR
    GCSE

    Wave speed represents the rate at which energy is transferred through a medium, quantified by the distance travelled per unit time or the product of frequency and wavelength. Candidates must manipulate the wave equation (v = fλ) and the distance-speed-time relationship (v = x/t) to solve for unknowns, ensuring strict adherence to SI units such as metres per second, Hertz, and metres. Mastery includes the experimental determination of wave speed in various media, such as using ripple tanks for water waves or timing echoes for sound. Furthermore, understanding that wave speed is primarily a property of the medium—remaining constant despite frequency changes in linear contexts—is essential for higher-level analysis.

    0
    Objectives
    4
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for correct substitution of values into the wave equation v = fλ
    • Credit responses that explicitly convert wavelength from centimetres or millimetres to metres before calculation
    • Award 1 mark for describing the measurement of frequency using a strobe light or frequency generator in a ripple tank context
    • Candidates must state that wave speed is the distance travelled by a wavefront per unit time, not just 'how fast it moves'
    • Award 1 mark for calculating the mean speed from multiple trials to reduce random error

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the equation, but check your units—wavelength must be in metres"
    • "Good calculation, but you must show the rearrangement step to secure the method mark if the final answer is wrong"
    • "You described measuring one wave; to improve accuracy and gain higher marks, describe measuring 10 waves and dividing by 10"
    • "Excellent use of standard form. Now consider why using a strobe light improves the accuracy of your frequency measurement"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for correct substitution of values into the wave equation v = fλ
    • Credit responses that explicitly convert wavelength from centimetres or millimetres to metres before calculation
    • Award 1 mark for describing the measurement of frequency using a strobe light or frequency generator in a ripple tank context
    • Candidates must state that wave speed is the distance travelled by a wavefront per unit time, not just 'how fast it moves'
    • Award 1 mark for calculating the mean speed from multiple trials to reduce random error

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When using v = fλ, always check if frequency is in kHz or MHz and convert to Hz immediately using standard form
    • 💡For 6-mark practical questions, explicitly state the measuring instrument (e.g., metre rule, stopwatch) alongside the variable being measured
    • 💡If given a diagram of a ripple tank, count the number of full waves between the first and last wavefront, not the number of lines
    • 💡Remember that sound waves in air travel at approximately 330-340 m/s; use this to sanity check your calculated answers

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Failing to convert wavelength from cm or mm into metres, resulting in answers incorrect by factors of 100 or 1000
    • Confusing the time period (T) with frequency (f) when calculating wave speed from time data
    • In practical descriptions, measuring the length of a single wave rather than measuring across multiple waves (e.g., 10 waves) to calculate a mean
    • Rearranging the equation v = fλ incorrectly, often dividing frequency by speed

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Application of the wave equation v = fλ
    Experimental measurement of sound and water waves
    Relationship between speed, distance, and time
    Unit conversion and standard form in wave calculations

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Describe
    Explain
    Suggest
    Determine

    Practical Links

    Related required practicals

    • •{"code":"PAG P8","title":"Measuring Wave Properties","relevance":"Direct assessment of measuring wave speed in liquids (ripple tank) and solids (metal rod)"}

    Ready to test yourself?

    Practice questions tailored to this topic