Ultrasound: sonar and scanning sim
Sail a model ship over a sea bed in a water tank, send ultrasound pulses and read the echo times on an oscilloscope to map the depth with d = v t ÷ 2; then slide a probe over a gel block to get echoes from every boundary inside (and none without gel), and over a steel bar to find a hidden crack.
Sound · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model. An echo comes back from a boundary d away after t = 2d ÷ v, so d = v t ÷ 2. Speeds: water 1500 m/s, soft tissue (and the gel block) 1540 m/s, steel 5900 m/s, air 340 m/s (textbook values, from memory). Sonar: the tank's water is 180 mm deep over seven concrete blocks 40, 64, 96, 110, 72, 28, 52 mm high; the transducer is 30 mm under the surface and its beam 12 mm wide, so it hears the highest block under it first. The times in the tank are real; the tank is also a 1 : 1000 model of the sea (1 mm stands for 1 m, and 1 ms on the screen for 1 s). Scanning: a fat-like layer 12 mm thick over a muscle-like layer, a fluid-filled cyst (radius 9 mm) and a small hard stone (radius 6 mm), on a rubber base that absorbs the pulse. How much of a pulse each boundary reflects comes from the acoustic impedances (beyond the syllabus: r = (Z₂ − Z₁) ÷ (Z₂ + Z₁), values from memory, the stone's chosen); without gel an air gap under the probe reflects almost all of it. The stone takes 95 % of what enters it (chosen). Testing: a steel bar 50 mm thick with a flat crack 20 mm down; the beam is 10 mm wide. The screen's height for an echo is on a log scale (beyond the syllabus). Readings: the start of each echo is read to 0.2 division with a seeded judging error of up to 0.08 division (chosen). The pulse is played slowed down 8 000 times (sonar) to 80 000 times (steel). Time never runs on its own: each pulse is one click.
- The part to watch: the model ship (sonar) or the hand probe (scanning and testing)
- Glass tank, concrete sea-bed blocks, gel block, steel bar, gel bottle, pulser–receiver, oscilloscope
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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