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QLDPhysicsQuick questions

Unit 2: Linear motion and waves

Quick questions on Wave properties: transverse and longitudinal mechanical waves (QCE Physics Unit 2)

10short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What are transverse waves?
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Particle motion is perpendicular to the direction of energy propagation. Examples: a wave on a rope or string, surface water waves (approximately), all electromagnetic waves. The wave has crests and troughs.
What are longitudinal waves?
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Particle motion is parallel to the direction of energy propagation. Examples: sound waves in air or water, the primary (P) waves in earthquakes, ultrasound. The wave has compressions (high pressure) and rarefactions (low pressure).
What is wavelength?
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Distance between two consecutive points in phase (crest to crest, compression to compression). SI unit: m.
What is period?
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Time for one complete cycle to pass a point. SI unit: s.
What is frequency?
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Number of cycles per second. f=1/Tf = 1/T. SI unit: hertz (Hz).
What is amplitude?
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Maximum displacement from equilibrium. SI unit: m for transverse, Pa for sound (pressure amplitude). Amplitude determines wave energy (energy ∝A2\propto A^2).
What is speed?
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Distance the wave moves per unit time. v=fλv = f \lambda. SI unit: m s−1^{-1}.
What is q1?
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Distinguish transverse from longitudinal mechanical waves with one example each. [2 marks]
What is q2?
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A wave on a string has wavelength 0.40 m0.40 \text{ m} and frequency 5.0 Hz5.0 \text{ Hz}. Calculate the speed, the period and the amplitude if the maximum displacement is 0.05 m0.05 \text{ m}. [3 marks]
What is q3?
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A Bremer River bridge accelerometer detects a 1.8 Hz1.8 \text{ Hz} transverse deck vibration. (a) Calculate the period. (b) Given a deck wave speed of 90 m s−190 \text{ m s}^{-1}, determine the wavelength and discuss whether the 50 m50 \text{ m} span supports a first-mode resonance.

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