3.4.4 Sound Speed, Echoes & Ultrasound
Test your understanding of echo calculations, measurement techniques, and ultrasound applications
A ship uses sonar to measure the depth of the ocean. The sonar pulse is sent downward and the echo returns after 0.8 seconds. The speed of sound in seawater is 1500 m/s. Calculate the depth of the ocean.
Students measure the speed of sound in air using the clapping-echo method. They stand 50 m from a wall, clap their hands, and use a stopwatch to measure the time for the echo to return. Explain why the time measured is often INACCURATE.
Doctors use ultrasound scanners instead of X-rays to monitor the development of unborn babies. State the main reason why ultrasound is preferred over X-rays for this application.
What is the MINIMUM frequency that defines ultrasound waves?
Engineers use ultrasound for Non-Destructive Testing (NDT) to detect cracks inside metal components. A crack is detected when the reflected ultrasound pulse returns SOONER than expected. Explain how this indicates the presence of a crack.
📋 EXAM TECHNIQUE REMINDERS
- • Echo calculations: ALWAYS divide by 2 (distance traveled is there-and-back)
- • Paper 6 errors: Focus on measurement limitations, not physics theory
- • Safety questions: Use keywords like "non-ionizing" for ultrasound vs X-rays
- • Definitions: Learn exact values (ultrasound = above 20 kHz)
- • NDT logic: Earlier echo = obstruction before the expected surface
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