This topic summary covers Knowledge Organiser: Seismic Waves within Seismic Waves for GCSE Physics. Revise Seismic Waves in Waves for GCSE Physics with 13 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Seismic Waves
Key Terms
- P-waves: longitudinal, travel through solids + liquids
- S-waves: transverse, solids only
- Shadow zone: region where waves don't arrive
- Seismograph: instrument detecting seismic waves
Earth's Layers
- Crust (thin, solid)
- Mantle (solid, thick)
- Outer core (LIQUID — S-wave evidence)
- Inner core (solid — P-wave evidence)
Key Evidence
- S-wave shadow zone → outer core is liquid
- P-wave shadow zone → core has different density
- P-waves still detected → inner core is solid
Exam Tips
- S = Stopped by liquid (transverse can't pass through liquid)
- P = Passes through everything (longitudinal)
- Always explain WHY waves can't pass through liquid
- Outer core = liquid; inner core = solid
Key Equations
- v = f × λ (wave speed = frequency × wavelength)
- P-waves: faster, longitudinal, travel through solids and liquids
- S-waves: slower, transverse, travel through solids only
- Wave speed increases with density/rigidity of medium
Common Mistakes
- Confusing P-wave and S-wave properties: P-waves are longitudinal (compressions) and travel through everything; S-waves are transverse and cannot travel through liquids — use "S = Stopped by liquid" as a memory aid
- Not explaining why S-waves can't pass through liquid: Transverse waves require a medium that can undergo shear stress — liquids cannot support transverse vibrations, so S-waves are absorbed at the outer core
- Confusing outer and inner core states: The outer core is liquid (S-waves are blocked here); the inner core is solid (S-waves could pass through but don't reach it directly)
- Saying seismic waves prove Earth's structure directly: Seismic wave evidence is indirect — we infer the structure from the pattern of which waves arrive where, not by drilling to the core
- Forgetting waves refract inside Earth: Seismic waves change direction (refract) as they travel through layers of different density — this creates shadow zones where no waves are detected
Practice questions for Seismic Waves
What type of wave is a P-wave (primary seismic wave)?
State two differences between P-waves and S-waves in terms of how the particles move and what materials they can travel through.
Quick recall flashcards
What are S-waves?
Secondary (transverse) seismic waves - slower
What are P-waves?
Primary (longitudinal) seismic waves - fastest