Free GCSE Physics lesson: Sound and Seismic Waves
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Lesson 44 · GCSE / Key Stage 4 · Physics

Sound, ultrasound and seismic waves

Compare sound, ultrasound and seismic waves, including reflection, echoes, imaging and Earth structure.

Qualification: GCSE Subject: Physics Waves

Waves

Lesson overview

This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.

FocusSound, ultrasound and seismic wave applications
Time45-60 minutes
EquipmentCalculator and wave-speed equation practice.
Practical linkNo separate practical method focus
Maths tagsM1 units and equation sense

What you will learn

  • Describe sound as a longitudinal wave.
  • Use echoes and time delay to calculate distance.
  • Explain ultrasound imaging and sonar in simple terms.
  • Compare P-waves and S-waves in seismic evidence.

Wave application scenarios supplied on this page

Use echo, ultrasound scan, sonar and earthquake examples to practise wave application explanations.

Sound, ultrasound and seismic waves infographic

Infographic explaining GCSE Physics sound, ultrasound and seismic waves, including longitudinal sound waves, the wave speed equation, echo distance calculations, ultrasound uses, P-waves, S-waves and Earth shadow-zone evidence.
Use this visual to compare sound and seismic wave models, apply echo calculations and explain Earth's liquid outer core evidence.Download visual

Clear explanation

Sound is a longitudinal wave that needs a medium. It cannot travel through a vacuum because there are no particles to vibrate.

Ultrasound has a frequency above human hearing. Reflected ultrasound pulses can build images or measure distances using time delay.

Seismic P-waves and S-waves travel differently through Earth. S-waves do not travel through liquids, which provides evidence about Earth's outer core.

Worked examples

Echo distance

A sound pulse takes 0.40 s to travel to a wall and back.

The total journey is twice the distance to the wall.

If sound speed is 340 m/s, total distance = 340 x 0.40 = 136 m.

Answer: The wall is 68 m away because the sound travelled there and back.

Quick checks

Choose an answer, then check your thinking.

1. Why can sound not travel through a vacuum?

2. Which seismic wave cannot travel through liquids?

Practice questions

Question 1

A sonar pulse returns after 0.20 s. The sound speed in water is 1500 m/s. How far away is the object?

Reveal answer and marking guidance

Answer: 150 m.

Marking: Credit total distance 1500 x 0.20 = 300 m, then halve for there-and-back journey.

Question 2

What is ultrasound?

Reveal answer and marking guidance

Answer: Sound with frequency above the upper limit of human hearing.

Marking: Credit frequency above about 20 kHz.

Question 3

Why are echoes useful in imaging or distance measurement?

Reveal answer and marking guidance

Answer: The reflected wave and its time delay show where a boundary or object is.

Marking: Credit reflection and time delay.

Question 4

What does the behaviour of S-waves suggest about Earth's outer core?

Reveal answer and marking guidance

Answer: The outer core is liquid because S-waves do not pass through it.

Marking: Credit S-wave evidence and liquid outer core.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply sound, ultrasound and seismic wave applications to an unfamiliar device, practical setup or data description.
Practical interpretationUse evidence, graph features, uncertainty, method quality or conclusion wording where the question asks you to evaluate.
Maths skillM1 units and equation sense

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.

Common mistakes

  • Forgetting to halve echo distances.
  • Calling sound transverse in air.
  • Thinking ultrasound is electromagnetic radiation.
  • Saying S-waves pass through liquids.

Extension challenge

Compare ultrasound scanning and X-ray imaging, including one advantage and one limitation of each.

Reveal answer

Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.

Exam-board guidance

Short board notes only. Learn the core physics above first.

AQA GCSE Physics

AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for sound, ultrasound and seismic wave applications.

OCR GCSE Physics

OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.

Eduqas GCSE Physics

Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.

WJEC Wales

WJEC Wales: often expects accurate terms, units and evidence-based explanations using the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.

Next lesson

Next, continue with Practical: Reflection and Refraction.

Previous lesson: Infrared PracticalBack to GCSE Physics lessonsNext lesson: Practical: Reflection and Refraction