Transverse & Longitudinal Waves (AQA GCSE Physics)

Transverse Waves

• Waves are repeated vibrations that transfer energy

• Energy is transferred by parts of the wave knocking nearby parts

  • This is similar to the effect of people knocking into one another in a crowd, or a "Mexican Wave" at football matches

• 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 perpendicular to 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

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 in 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 waves are represented as a continuous solid line

Longitudinal Waves

• 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 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

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

Transverse v Longitudinal Waves

• Their different motions can be shown on ropes (transverse) and springs (longitudinal)

Waves can be shown through vibrations in ropes or springs

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

Transverse Waves v Longitudinal Waves Table

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