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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)
11short 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 is transverse waves?Show answer
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 is longitudinal waves?Show answer
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?Show answer
Distance between two consecutive points in phase (crest to crest, compression to compression). SI unit: m.
What is period?Show answer
Time for one complete cycle to pass a point. SI unit: s.
What is frequency?Show answer
Number of cycles per second. $f = 1/T$. SI unit: hertz (Hz).
What is amplitude?Show answer
Maximum displacement from equilibrium. SI unit: m for transverse, Pa for sound (pressure amplitude). Amplitude determines wave energy (energy $\propto A^2$).
What is speed?Show answer
Distance the wave moves per unit time. $v = f \lambda$. SI unit: m s$^{-1}$.
What is confusing amplitude with wavelength?Show answer
Amplitude is the height of a crest (perpendicular to motion for transverse). Wavelength is the horizontal distance between repeats.
What is treating speed as a property of the wave?Show answer
Wave speed is a property of the medium, not the source. A whistle and a piano playing the same note have the same wavelength in the same air.
What is calling sound transverse?Show answer
Sound is longitudinal in air, water and solids in compression. Solids can also carry transverse sound (S-waves), but the air-borne sound we hear is longitudinal.
What is mixing $f$ and $T$ on the calculator?Show answer
A $2$ Hz wave has a period of $0.5$ s, not $2$ s.