Waves

• Waves

  Oscillations or vibrations about a fixed point
• Waves transfer energy and information
• Waves do not transfer matter
• Transverse waves

  • The motion of the wave is perpendicular to the direction of energy transfer of the wave
• Both transverse and longitudinal waves transfer energy, but not the particles of the medium
• The motion of the wave causes the particles to move, but the particles themselves are not the wave
• Demonstrating wave motion

  1. Using ropes (transverse) and springs (longitudinal)

  2. Using water waves in a ripple tank
• Crest (Peak)

  The highest point on a wave above the equilibrium, or rest, position
• Trough

  The lowest point on a wave below the equilibrium, or rest, position
• Amplitude

  The distance from the undisturbed position to the peak or trough of a wave
• Wavelength

  The distance from one point on the wave to the same point on the next wave
• Frequency

  The number of waves passing a point in a second
• Wave speed

  The speed at which energy is transferred through a medium
• Frequency is the number of waves passing through a point per second.
• Transverse waves

  Waves where the points along its length vibrate at 90 degrees to the direction of energy transfer
• Transverse waves

  • 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
• Transverse wave features

  • The highest point above the rest position is called the peak or crest
  • The lowest point below the rest position is called the trough
• Examples of transverse waves

  • 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)
• The curves are drawn so that they are perpendicular to the direction of energy transfer
• Longitudinal waves

  Waves where the points along its length vibrate parallel to the direction of energy transfer
• Longitudinal waves

  • 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)
• Longitudinal wave features

  • Close together points are called compressions
  • Spaced apart points are called rarefactions
• Examples of longitudinal waves

  • Sound waves
  • P-waves (a type of seismic wave)
  • Pressure waves caused by repeated movements in a liquid or gas
• 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
• 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.
• Wave interference occurs when two or more waves meet at the same point in space, resulting in the superposition of the waves.
• Constructive interference happens when waves combine to form a wave with a larger amplitude, while destructive interference results in a wave with a smaller or zero amplitude.
• Interference patterns can be observed in various wave phenomena such as light waves, sound waves, and water waves.
• Wave speed

  The distance travelled by a wave each second
• Wave speed unit

  metres per second (m/s)
• Wave speed

  The speed at which energy is transferred through a medium
• Wave equation

  v = f × λ
• v


  Wave speed in metres per second (m/s)
• f


  Frequency in Hertz (Hz)
• λ


  Wavelength in metres (m)
• Calculating wave frequency


  f = 1 / T
• Be careful with units: wavelength is usually measured in metres and speed in m/s, but if the wavelength is given in cm you might have to give the speed in cm/s
• Waves


  • Can be reflected
  • Can be refracted
  • Can be diffracted
• Reflection


  A wave hits a boundary between two media and does not pass through, but instead stays in the original medium