Transverse & Longitudinal Waves
- Waves are repeated vibrations that transfer energy
- Waves can exist as one of two types:
- Transverse
- Longitudinal
Transverse Waves
- Transverse waves have vibrations that are at 90° to the direction of travel
- Transverse waves:
- Vibrate perpendicularly to the direction of travel
- Transfer energy, but not the particles of the medium
- Mechanical waves move in solids and on the surfaces of liquids but not through liquids or gases
- Electromagnetic waves are transverse waves that 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
Example 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 in a guitar string
- S-waves (a type of seismic wave)
- Electromagnetic waves (such as radio, light, X-rays etc)
Longitudinal Waves
- Longitudinal waves have vibrations that are parallel to the direction of travel
- Longitudinal waves:
- Vibrate in the same direction as the direction of travel
- Transfer energy, but not the particles of the medium
- 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 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
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 the direction the wave travels | Parallel to the direction the wave travels |
| Vacuum | Only electromagnetic waves can travel in a vacuum | Cannot travel in a vacuum |
| Material | Con move in solids and the surface of liquids (electromagnetic waves can move in solids, liquids and gases) | Con move in solids, liquids and gases |
| Speed of wave | Depends on material it is travelling in | Depends on material it is travelling in |
Worked example
Both transverse and longitudinal waves can travel on the surface of water. The diagram below shows a toy duck bobbing up and down on top of the surface of some water.
Explain how the toy duck demonstrates that waves do not transfer matter.
Answer:
Step 1: Identify the type of wave
- The type of wave on the surface of a body of water is a transverse wave
- This is because the duck is moving perpendicular to the direction of the wave
Step 2: Describe the motion of the toy duck
- The plastic duck moves up and down but does not travel with the wave
Step 3: Explain how this motion demonstrates that waves do not transfer matter
- Both transverse and longitudinal waves transfer energy, but not the particles of the medium
- This means when a wave travels between two points, no matter actually travels with it, the points on the wave just vibrate back and forth about fixed positions
- Objects floating on the water simply bob up and down when waves pass under them, demonstrating that there is no movement of matter in the direction of the wave, only energy
Examiner Tip
The key difference between transverse and longitudinal waves is the direction of the vibrations with respect to the direction of the wave itself. For transverse waves, these are perpendicular to each other, whilst for longitudinal waves, these are parallel.
