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Course: OCR A Level Physics A H556
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OCR A Level Physics A H556

1. Development of Practical Skills in Physics

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2. Foundations in Physics

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3. Forces and Motion

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4. Electrons, Waves and Photons

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OCR H556 chapter questions and answers

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Text lesson

4.6.1 Progressive Waves: Longitudinal and Transverse

4.6.1 Progressive Waves: Longitudinal and Transverse: Describe progressive waves as energy transfer without net movement of matter, and distinguish transverse from longitudinal waves with examples.

4.6.1 Progressive Waves: Longitudinal and Transverse

Waves move energy through a material while the material itself stays roughly where it was.

Energy transfer
  • A progressive wave carries energy and information from one place to another by a repeating disturbance.
No net matter flow
  • Particles of the medium oscillate about fixed positions and do not travel along with the wave.
Source
  • Every wave starts from an oscillating source, and each particle repeats the motion of the one before it slightly later.
Medium
  • Mechanical waves need a medium to pass through, whereas electromagnetic waves can cross a vacuum.
Transverse and Longitudinal
Transverse
  • The oscillations are at right angles to the direction of energy transfer, as with ripples, light and a plucked string.
Longitudinal
  • The oscillations are parallel to the direction of energy transfer, as in sound and a pushed spring.
Peaks and troughs
  • Transverse waves have crests and troughs, which are the points of maximum positive and negative displacement.
Compressions
  • Longitudinal waves have compressions where particles are close together and rarefactions where they are spread apart.
Feature Transverse Longitudinal
Oscillation direction Perpendicular to travel Parallel to travel
Examples Light, water ripples, string waves Sound, ultrasound, seismic P-waves
Can be polarised Yes No
1

Displacement is the distance of a point from its equilibrium position, measured in a stated direction.
2

Amplitude is the maximum displacement from equilibrium and relates to the energy carried.
3

Wavelength is the distance between two successive points oscillating in phase, such as adjacent crests.
4

Period is the time for one complete oscillation, and frequency is the number of oscillations per second.
5

Wave speed is the distance the wave pattern travels per unit time and depends mostly on the medium.

4.6.1 – Key Points for the Exam

  • Progressive wave: A wave that transfers energy from one place to another.
  • Transverse wave: A wave in which oscillations are perpendicular to the direction of energy transfer.
  • Longitudinal wave: A wave in which oscillations are parallel to the direction of energy transfer.
  • Amplitude: The maximum displacement of a point from its equilibrium position.
  • Wavelength: The distance between adjacent points that are in phase.

Common Mistakes

  • Saying the medium travels along with the wave; only the energy moves.
  • Calling a compression the same as a crest; compressions occur only in longitudinal waves.
  • Measuring wavelength from a crest to the next trough, which is only half a wavelength.
  • Believing sound can travel through a vacuum.
YOUR STUDY PATH

4.6.1 Progressive Waves: Longitudinal and Transverse

OCR A Level Physics A H556 / 4. Electrons, Waves and Photons

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