Wave Model

• Frequency and period of a travelling wave

  Related by the equation: f = 1/T
• Travelling waves are defined as oscillations that transfer energy from one place to another without transferring matter
• Wavelength

  The length of one complete oscillation measured from the same point on two consecutive waves, measured in metres (m)
• Wave speed and wavelength

  • As the wavelength increases, the frequency decreases
  • As the wavelength decreases, the frequency increases
• Travelling waves

  • Waves transfer energy, not matter
  • Waves are generated by oscillating sources
  • Oscillations can propagate through a medium or in vacuum, depending on the type of wave
• Wave speed

  The distance travelled by the wave per unit time, measured in metres per second (m/s)
• Amplitude


  The maximum displacement of an oscillating wave from its equilibrium position, measured in metres (m)
• The wave equation tells us that for a wave of constant speed, as the wavelength increases, the frequency decreases and as the wavelength decreases, the frequency increases
• Period & Frequency

  1. Period (T) is the time taken for a fixed point on the wave to undergo one complete oscillation, measured in seconds (s)

  2. Frequency (f) is the number of full oscillations per second, measured in Hertz (Hz)
• Displacement

  The distance of a point on the wave from its equilibrium position, measured in metres (m)
• Wave equation


  v = fλ = λ/T
• Relationship between frequency f and period T


  f = 1 / T
• Amplitude


  The maximum displacement from the equilibrium position (x = 0)
• Identifying the period T of the wave on the graph

  The period is defined as the time taken for one complete oscillation to occur
• Longitudinal waves need particles to propagate, so they cannot travel through a vacuum. This is why you cannot hear anything in the vacuum of outer space
• Transverse waves

  • Electromagnetic waves e.g. radio, visible light, UV
  • Vibrations on a guitar string
• Longitudinal waves

  A wave in which the particles oscillate parallel to the direction of motion and energy transfer
• Particles in a transverse wave move up and down. Particles in a longitudinal wave move left and right. The particles do not travel 'along' the wave, they are just in one position, and can only move either vertically or horizontally. All the particles have the same motion, but are displaced slightly, creating the illusion that the whole wave is moving together
• Transverse waves

  • Show areas of peaks and troughs
  • Transfer energy, even if there is no resultant displacement of the medium
  • Do not need particles to propagate, so they can travel through a vacuum
• Longitudinal waves

  1. Each particle in the wave only vibrates left and right

  2. Areas of low and high pressure can be observed: Rarefaction is an area of low pressure, with the particles being further apart from each other

  3. Compression is an area of high pressure, with the particles being closer to each other
• This is why we can still feel the UV radiation from the Sun, as it can travel through the vacuum of space
• Transverse waves

  Each particle in the wave vibrates up and down
• Longitudinal waves

  • Sound waves
• The frequency of a sound wave is related to its pitch

  • Sounds with a high pitch have a high frequency (or short wavelength)
  • Sounds with a low pitch have a low frequency (or long wavelength)
• The higher the air temperature


  The greater the speed of sound
• Sound wave propagation

  Travels with a series of compressions and rarefactions
• Electromagnetic waves are generated by the combined oscillation of an electric and a magnetic field
• Humans can only sense electromagnetic waves with wavelengths in the range 700 nm - 400 nm, which are the limits of the visible spectrum
• Sounds with frequencies below and above the audible range cannot be detected by the human ear
• Sound waves travel at a speed of about 340 m/s in air at room temperature
• Sound waves are generated by oscillating sources, which produce a change in density of the surrounding medium
• Sound travels the slowest in gases


  Since gas particles are spread out and less efficient in transferring the oscillations to their neighbours
• The shorter the wavelength, or higher the frequency, the greater the energy of the wave
• All electromagnetic waves travel at the speed of light in vacuum
• The amplitude of a sound wave is related to its volume

  • Sounds with a large amplitude have a high volume
  • Sounds with a small amplitude have a low volume
• Sound travels the fastest through solids

  Since solid particles are closely packed and can pass the oscillations onto their neighbours much faster
• Sound waves are longitudinal waves and require a medium in which to propagate
• Humans can only hear sounds with frequencies in the range 20 Hz - 20 kHz, known as the audible range
• Electromagnetic waves are transverse waves and can travel through vacuum
• Electromagnetic waves with longer and shorter wavelengths are invisible to the human eye