Transverse & Longitudinal Waves (Cambridge O Level Physics)

• Waves are repeated vibrations that transfer energy

• Waves can exist as one of two types:
  • Transverse
  • Longitudinal

Transverse Waves

• Transverse waves are defined as:

Waves where the points along its length vibrate at 90 degrees to the direction of energy transfer

• For a transverse wave:
  • The energy transfer is in the same direction as the wave motion
  • They transfer energy, but not the particles of the medium
  • They can move in solids and on the surfaces of liquids but not inside liquids or gases
  • Some transverse waves (electromagnetic waves) can move in solids, liquids and gases and in a vacuum

• The point on the wave that is:
  • The highest above the rest position is called the peak, or crest
  • The lowest below the rest position is called the trough

Vibrations of a Transverse Wave

Transverse waves can be seen in a rope when it is moved quickly up and down

• Examples of transverse waves are:
  • Ripples on the surface of water
  • Vibrations on a guitar string
  • S-waves (a type of seismic wave)
  • Electromagnetic waves (such as radio, light, X-rays etc)

Representing Transverse Waves

• Transverse waves are drawn as a single continuous line, usually with a central line showing the undisturbed position
• The curves are drawn so that they are perpendicular to the direction of energy transfer
  • These represent the peaks and troughs

Transverse Wave Graph

Transverse waves are represented as a continuous solid line

• Longitudinal waves are defined as:

Waves where the points along its length vibrate parallel to the direction of energy transfer

• For a longitudinal wave:
  • The energy transfer is in the same direction as the wave motion
  • They transfer energy, but not the particles of the medium
  • They can move in solids, liquids and gases
  • They can not move in a vacuum (since there are no particles)

• The key features of a longitudinal wave are where the points are:
  • Close together, called compressions
  • Spaced apart, called rarefactions

Longitudinal Wave on a Spring

Longitudinal waves can be seen in a slinky spring when it is moved quickly backwards and forwards

• Examples of longitudinal waves are:
  • Sound waves
  • P-waves (a type of seismic wave)
  • Pressure waves caused by repeated movements in a liquid or gas

Representing Longitudinal Waves

• Longitudinal waves are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer
  • Drawing the lines closer together represents the compressions
  • Drawing the lines further apart represents the rarefactions

Diagram of a Longitudinal Wave

Longitudinal waves are represented as sets of lines with rarefactions and compressions

Comparing Transverse & Longitudinal Waves

• The different properties of transverse and longitudinal waves are shown in the table:

Transverse Waves v Longitudinal Waves Table

Property	Transverse Waves	Longitudinal Waves
Structure	Peaks and troughs	Compressions and rarefactions
Vibration	90° to direction of energy transfer	Parallel to direction of energy transfer
Vacuum	Electromagnetic waves (a transverse wave) can travel through a vacuum	Cannot travel in a vacuum
Material	Can move in solids, liquids and gases	Can move in solids, liquids and gases
Density	Constant density	Changes in density
Pressure	Constant pressure	Changes in pressure
Speed of wave	Dependent on the material it travels in	Dependent on the material it travels in