GCSE Physics: Sound, Ultrasound and Seismic Waves

This material covers the mechanical waves in GCSE Physics that are not part of the electromagnetic spectrum: sound, ultrasound and seismic waves. Much of it is separate (triple) physics content, for example in AQA's specification, with the uses of ultrasound and seismic waves marked as Higher tier there.

It begins with sound itself. Sound is a longitudinal wave made of compressions and rarefactions, so it needs a medium and cannot cross a vacuum. It travels faster in solids than in gases, and when it passes from one medium to another its speed and wavelength change while its frequency stays the same. You apply the range of normal human hearing, about 20 Hz to 20 kHz, converting kilohertz to hertz, and at Higher tier you explain that sound makes the eardrum and other parts of the ear vibrate, and that this only works over a limited range of frequencies.

Echoes are the thread that links the calculations. Every echo question relies on the same idea: the time measured is for the journey there and back, so the one-way distance is half of speed × time. You use this for a clap echoing off a wall, for echo sounding of the sea floor, and for ultrasound finding a flaw inside a metal block. Ultrasound is sound above 20 kHz. It is partly reflected at each boundary between different materials, and the timing of the reflections builds an image. You explain why it is used to scan a foetus rather than X-rays: X-rays are ionising and ultrasound is not.

The last section is about earthquakes. P-waves are longitudinal and travel through solids and liquids; S-waves are transverse and cannot travel through liquids. The S-wave shadow zone on the far side of the Earth from an earthquake is evidence that the outer core is liquid, and the refraction of P-waves inside the Earth gives further clues to its structure.

The material offers three formats. The quiz has 12 questions mixing single-answer and multiple-answer items, each with an explanation. The flashcards give quick revision of the key facts. The written work is a printable sheet of 8 longer questions, including an echo method for measuring the speed of sound, wavelength changes between air and water, an ultrasound thickness calculation and an extended explanation of seismic shadow zones, which you answer by hand and upload for feedback on each answer.

• Describe sound as a longitudinal wave that needs a medium, and explain what changes when it enters a new medium
• Use the range of human hearing and (Higher) explain how the ear responds to sound
• Calculate distances, depths and speeds from echo times, remembering the return journey
• Explain how ultrasound is used for imaging and why it is used for scanning a foetus
• Describe P-waves and S-waves and explain how shadow zones show that the outer core is liquid

Practice material written by Zestly, based on the DfE GCSE physics subject content (waves: sound waves, uses of ultrasound, seismic waves), with AQA GCSE Physics 8463 used as the example specification.