Transverse & Longitudinal Waves (AQA GCSE Physics): Revision Note

Transverse Waves

• Waves can exist as one of two types:

  • Transverse waves

  • Longitudinal waves

Transverse waves

• Transverse waves are defined as:

Waves which vibrate at right angles to the direction of energy transfer

• Transverse waves:

  • vibrate perpendicular (at right angles) to the direction of travel

  • transfer energy, but not matter (the particles of the medium)

  • can exist as mechanical waves, which can move in solids and on the surfaces of liquids but not inside liquids or gases

  • can exist as electromagnetic waves, which can move in solids, liquids, gases, and in a vacuum

• On a transverse wave:

  • the highest point above the rest position is called a peak or crest

  • the lowest point below the rest position is called a trough

Example of a transverse wave

Transverse waves can be demonstrated on 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 (at 90 degrees) to the direction of energy transfer

  • These represent the peaks and troughs

Transverse wave crests and troughs

Transverse waves are represented as a continuous solid line with crests and troughs

Longitudinal Waves

• Longitudinal waves are defined as:

Waves which vibrate parallel to the direction of energy transfer

• Longitudinal waves:

  • vibrate in the same direction as the direction of travel

  • transfer energy, but not matter (the particles of the medium)

  • can move in solids, liquids and gases

  • cannot 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

Example of a longitudinal wave

Longitudinal waves can be demonstrated in a slinky spring when it is moved quickly backwards and forward

• 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

Longitudinal wave rarefactions and compressions

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

Transverse v Longitudinal Waves

• Wave vibrations can be demonstrated on ropes (transverse) and springs (longitudinal)

A comparison of longitudinal and transverse waves

Wave motion can be demonstrated through vibrations in ropes or springs

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

Properties of transverse and longitudinal waves

Wavefronts

• Both transverse and longitudinal waves can be represented as wavefronts

  • This is where the waves are viewed from above

• For a transverse wave:

  • One line represents either a peak or a trough

• For a longitudinal wave:

  • One line represents either a compression or a rarefaction

• The arrow shows the direction the wave is moving and is sometimes called a ray

• The space between the lines represents the wavelength

  • When the lines are close together, this is a wave with a short wavelength

  • When the lines are far apart, this is a wave with a long wavelength

Wavefronts as viewed from above

Diagram showing a wave moving to the right, drawn as a series of wavefronts