AQA AS Level Physics Paper 2, June 2025: Question 22

1 mark · Easy difficulty · Multiple Choice

Identify which property is not true for longitudinal waves among polarisation, interference, diffraction, and forming stationary waves.

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Question

Multiple-choice question 22 asking: 'Which is not true for longitudinal waves?' Four options are provided: A 'They can be polarised.', B 'They produce interference patterns.', C 'They can be diffracted.', and D 'They form stationary waves.' Each option is accompanied by an oval selection box, worth 1 mark.

Mark scheme

Show the mark scheme Mark scheme table row for question 22 showing answer 'A', text 'They can be polarised.', and assessment objective 'AO1'.

How to answer it

AQA AS Level Physics • Waves • Multiple Choice

Properties of Longitudinal Waves & Polarisation

What this question tests

This question assesses your understanding of fundamental wave phenomena and your ability to distinguish between transverse and longitudinal waves:

  • Universal wave behaviours: Recognising that reflection, refraction, diffraction, interference, and stationary wave formation occur in all waves (both transverse and longitudinal).
  • Polarisation: Knowing that polarisation is a property exclusive to transverse waves, where oscillations can be confined to a single plane perpendicular to the direction of energy transfer.

Question 22 Breakdown

Identifying non-characteristics of longitudinal waves [1 Mark]

✅ Correct Answer

A: They can be polarised.

Because longitudinal waves oscillate parallel to the direction of wave travel, there is no oscillation across multiple perpendicular planes. Therefore, longitudinal waves cannot be polarised. Since the question asks which statement is not true, A is the correct option.

💡 Key Knowledge

  • Longitudinal Waves: Particle displacement/oscillation is parallel to the direction of energy propagation (e.g., sound waves, ultrasound).
  • Transverse Waves: Particle displacement or field oscillation is perpendicular to the direction of energy propagation (e.g., EM waves, waves on a string).
  • Polarisation: Restricting oscillations to one single plane perpendicular to the direction of propagation. This can only happen if oscillations are perpendicular to travel (transverse).

🧠 Option Elimination & Exam Technique

  • Watch the negative stem: The question asks which is not true. Always circle or underline negative keywords like "not", "incorrect", or "false".
  • Option B (Interference patterns): True for longitudinal waves. Sound waves from two coherent speakers produce regions of constructive and destructive interference (loud and quiet spots).
  • Option C (Diffracted): True for longitudinal waves. Sound waves diffract through doorways and around obstacles easily because their wavelength is comparable to the aperture size.
  • Option D (Stationary waves): True for longitudinal waves. Stationary sound waves routinely form inside organ pipes, flutes, and resonance tubes (nodes and antinodes of displacement/pressure).

❌ Common Errors & Misconceptions

  • Confusing Stationary Waves with Transverse Only: Many students think stationary waves only occur on vibrating strings (transverse). Remember: stationary sound waves in resonance tubes are purely longitudinal!
  • Overlooking General Wave Phenomena: Forgetting that diffraction, refraction, and superposition/interference are universal wave properties exhibited by both types of waves.
  • Missing the Negative Stem: Quickly spotting that Option B, C, or D is true of longitudinal waves and accidentally selecting one of them as a "correct fact" instead of answering which is not true.
Mark Scheme Breakdown (AO1):
  • A (They can be polarised.) — 1 Mark [AO1: Knowledge and understanding of scientific principles]
  • Examiner Note: Polarisation is the standard definitive experimental test used to prove that an unknown wave is transverse rather than longitudinal.

Topics

Physics · 3.3 Waves

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.