Transverse & Longitudinal Waves (Edexcel GCSE Physics: Combined Science)

• 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

Comparing Transverse & Longitudinal Waves

• Wave vibrations 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

Step 1: Recall if a P-wave is transverse or longitudinal

• • P-waves are longitudinal waves

Step 2: Recall the definition of longitudinal waves

• • Points along longitudinal waves vibrate parallel to the direction of energy transfer
  • This means the rock vibrates in a line parallel to the direction of the P-wave drawn

Step 3: Draw arrows at the point labelled R to show it vibrating in parallel to the direction of the P-wave

• • This is shown in the image below