Define — 3 marks
A sonar system on a research vessel uses sound waves to detect underwater objects. The sound waves travel through seawater at different speeds depending on temperature and salinity. Scientists need to understand how these waves behave in the fluid medium to accurately map the ocean floor.
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(a) Define what is meant by a longitudinal wave.
[1 mark]
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(b) Define the term wavelength.
[1 mark]
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(c) Explain why sound waves, such as those used in the sonar system, are longitudinal waves and cannot travel through a vacuum.
[1 mark]
Show mark scheme
- (a) A wave where particles oscillate/vibrate parallel to the direction of energy transfer/wave propagation
- (b) The distance between two consecutive points in phase / the distance between successive compressions (or rarefactions)
- (c) Sound waves require a medium (particles) to vibrate/oscillate to transmit the wave; a vacuum has no particles/matter to oscillate
Suggest — 2 marks
A seismic monitoring station detects vibrations from an earthquake. The station records both P-waves (primary waves) and S-waves (secondary waves) arriving at different times. P-waves travel through both solid rock and liquid magma in the Earth's interior, whereas S-waves only travel through solid rock. Scientists use the time difference between the arrival of these two wave types to locate the earthquake's epicentre and determine the structure of the Earth's interior.
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(a) Suggest why S-waves cannot travel through the liquid outer core of the Earth, whereas P-waves can.
[1 mark]
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(b) Suggest one reason why the time difference between P-wave and S-wave arrival times increases with greater distance from the earthquake epicentre.
[1 mark]
Show mark scheme
- (a) S-waves are transverse waves and require a solid medium / particles oscillating perpendicular to direction of travel, which cannot occur in a liquid where particles can flow freely
- (a) OR P-waves are longitudinal waves and can travel through any medium (solid or liquid) as they only require compression and rarefaction
- (b) P-waves travel faster than S-waves, so over a greater distance the faster P-wave travels proportionally further ahead, increasing the time gap between arrivals
- (b) OR S-waves travel more slowly / at a lower speed, so take longer to cover the same distance as P-waves
Explain — 2 marks
A geologist uses seismic waves to investigate the structure of the Earth after an earthquake. Two types of waves are detected: primary waves (P-waves) that travel through both solids and liquids, and secondary waves (S-waves) that only travel through solids. The S-waves cannot pass through the Earth's liquid outer core, creating a 'shadow zone' where they are not detected.
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(a) Explain why S-waves cannot travel through the liquid outer core of the Earth.
[1 mark]
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(b) Explain why P-waves are able to travel through both the solid mantle and the liquid outer core.
[1 mark]
Show mark scheme
- (a) S-waves are transverse waves that require particles to oscillate perpendicular to the direction of wave travel / require a medium with shear strength
- (a) Liquids cannot support shear stress / have no fixed shape / particles can flow freely past each other
- (a) Therefore S-waves cannot propagate through liquids
- (b) P-waves are longitudinal waves that cause particles to oscillate parallel to the direction of wave travel
- (b) Longitudinal waves can travel through any medium (solids, liquids and gases) because they only require compression and rarefaction
- (b) Both solids and liquids can be compressed, so P-waves pass through both
Evaluate — 4 marks
A sound engineer is designing a concert hall and needs to choose between two materials for the walls: material A (a rigid concrete surface) and material B (a soft foam composite). The engineer wants to reduce unwanted echoes and reverberation while maintaining good sound quality for the audience.
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(a) Explain how sound waves behave differently when they encounter material A (concrete) compared to material B (foam).
[1 mark]
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(b) Evaluate which material would be more suitable for reducing echoes in the concert hall. Consider both the wave properties involved and the practical implications for sound quality.
[2 marks]
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(c) Suggest one limitation of using material B exclusively throughout the entire concert hall, and explain your answer in terms of wave behaviour.
[1 mark]
Show mark scheme
- (a) Concrete reflects/bounces sound waves; foam absorbs/dampens sound waves (accept: foam reduces amplitude of reflected waves)
- (b) Material B (foam) is more suitable because it absorbs sound energy, reducing reflections and therefore echoes
- (b) Foam prevents constructive interference from reflected waves that would cause reverberation / concrete causes multiple reflections leading to echoes
- (c) Foam absorbs too much sound, making the hall acoustically 'dead' / sound waves would lose too much energy and the audience would not hear the performance clearly / some reflection is needed for sound to travel effectively to all areas
Evaluate — 4 marks
A student investigates sound waves produced by a tuning fork. The tuning fork vibrates in air, creating compressions and rarefactions that travel outward. The student counts 45 complete oscillations in 0.3 seconds and measures the distance between consecutive compressions as 0.8 m.
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(a) Calculate the frequency of the tuning fork. Show your working.
[2 marks]
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(b) Evaluate whether sound is a transverse or longitudinal wave. Use evidence from the tuning fork investigation to support your answer.
[2 marks]
Show mark scheme
- (a) Correctly identifies that frequency = number of oscillations ÷ time (f = n/t)
- (a) Correctly calculates f = 45 ÷ 0.3 = 150 Hz
- (b) Identifies that sound is a longitudinal wave
- (b) Provides evidence that compressions and rarefactions are produced (characteristic of longitudinal waves where particles oscillate parallel to the direction of energy transfer), OR states that sound requires a medium and particles vibrate back and forth along the direction of wave travel
GCSE Perfect