Cambridge O Level Physics · Syllabus 5054 · Waves
Longitudinal Wave
What is Longitudinal Wave?
A longitudinal wave is one in which the direction of vibration is parallel to the direction of energy transfer, producing regions of compression and rarefaction; examples include sound waves and seismic P-waves.
This definition is part of the Waves chapter in Cambridge O Level Physics.
Common mistakes with Longitudinal Wave
- 3. “Particles in a longitudinal wave follow a sinusoidal path.” Why wrongThe smooth curve drawn for a longitudinal wave is a graph of pressure or displacement against position, not a picture of a particle’s trajectory. CorrectEach particle moves back and forth along a straight line, parallel to the direction of energy transfer. Say this“In a longitudinal wave the particles vibrate parallel to the direction of energy transfer; the curve is a graph, not a path.” CheckSound travels east. State the direction in which an air molecule oscillates.
Examiner tips on Longitudinal Wave
- Answering “state the difference”. A difference needs both halves and a stated reference direction. “Transverse vibrates up and down” states nothing on its own, because up and down is meaningless without saying what it is relative to. Write: “In a transverse wave the vibration is at right angles to the direction of energy transfer; in a longitudinal wave the vibration is parallel to it.”
Questions students ask about Longitudinal Wave
What is the difference between a transverse wave and a longitudinal wave?
In a transverse wave the particles vibrate at right angles to the direction of energy transfer, as in electromagnetic radiation, water-surface waves and seismic S-waves. In a longitudinal wave the particles vibrate parallel to the direction of energy transfer, producing compressions and rarefactions, as in sound waves and seismic P-waves. Both types transfer energy without transferring matter, and both obey \(v = f\lambda\).