Transverse & Longitudinal waves

• Transverse waves:

  The oscillations (vibrations) are perpendicular (at 90 degrees) to the direction of energy transfer.

  The vibrations are at right angles to the direction of wave travel.
• Examples of transverse waves:

  • All electromagnetic waves
  • Ripples and waves in water
  • Seismic S-waves
  • Vibrations in a guitar string
  • Light waves
• What a transverse wave look like:

  
• Longitudinal waves

  The oscillations (vibrations) are parallel to the direction of wave transfer.
• Examples of longitudinal waves:

  • Sound waves
  • Seismic P-waves
  • Ultrasound waves
• What a longitudinal wave looks like:

  
• All waves transfer energy from one place to another
• Ripples transfer kinetic energy.

  Sound waves transfer sound energy.
• Longitudinal waves show areas of compression and rarefaction:

  • compressions are regions of high pressure due to particles being close together.
  • rarefactions are regions of low pressure due to particles being spread further apart.
• All longitudinal waves require a medium to travel in such as air, water, or a solid.
• Not all transverse waves require a medium.
• For both ripples on a water surface and sound waves in air, it's the wave that travels and not the water or air
• Amplitude

  Amplitude is a measurement of the amount of energy transferred by a wave. It's the distance between the trough and equilibrium.
• Wavelength

  Wavelength is the distance from one crest to another, or from one trough to another, of a wave.

  The symbol for it is a Greek letter lambda (λ)
• We can measure the wavelength of the wave from the top bottom or middle.

  
• We can also measure the wavelength on longitudinal waves.

  We can measure from one compression to the next compression or from one rarefaction to the next rarefaction.
• Frequency

  The number of waves passing a point each second.

  Unit of frequency id Hertz (Hz).

  1Hz= 1 wave per second
• Period

  Time in seconds for one wave to pass a point.

  period = 1/frequency

  (s) (Hz)
• Wave speed

  Is the speed at which the wave moves through the medium (speed at which energy is transferred).
• This is the equation for wave speed:

  Wave speed =frequency x wavelength

  v = f x λ

  (m/s) (Hz) (m)
• How to measure the speed of sound waves in air:

  • Put 2 people 500m apart
  • Person A should hold a pair of cymbals and person B should hold a timer.
  • Person B should start timing when they see person A clash the cymbals together.
  • Person B then stops timing when they hears the sound of the cymbals clashing.
  • Then calculate the speed of the sound waves by dividing the distance travelled by the time taken.
• There are some problems with this experiment though:

  • Every person has a different reaction time.
  • It takes a fraction of a second between seeing the cymbals and starting the timer. It also takes half a second between hearing the sound and stopping the timer.
• We can reduce this error by having a large number of observers with timers. we take all of their results and discard any that are anomalous. We then calculate the mean.