A museum conservator uses a pulse-echo instrument on a laminated wooden panel made of two sections, A and B. The instrument sends an ultrasound pulse from the outer face of section A. The pulse crosses section A and then section B, reflects from the far face of section B, and returns to the instrument along the same path.
| Section | Thickness | Speed of ultrasound |
|---|---|---|
| A | 12 mm | 3000 m/s |
| B | unknown | 4000 m/s |
The echo is detected 20 μs20\ \mu\mathrm{s}20 μs after the pulse is sent.
What is the thickness of section B?
18 mm18\ \mathrm{mm}18 mm
24 mm24\ \mathrm{mm}24 mm
40 mm40\ \mathrm{mm}40 mm
48 mm48\ \mathrm{mm}48 mm
112 exam-style questions on Edexcel GCSE Physics 4.3 Sound, ultrasound and infrasound, covering 4.3.1 Sound waves, vibrations and the human ear, 4.3.2 Ultrasound and infrasound, 4.3.3 Uses of ultrasound and infrasound, and 4.3.4 Sound waves passing between media. Each one has a worked solution and a mark scheme showing where the marks go.