Wave Model

Basic Waves

  • Waves: oscillations that transfer energy, but not matter, throughout space and time
  • Mechanical Waves: waves that need a medium (e.g. air or water) to travel through
  • Transverse Waves: waves whose particles oscillate perpendicular to the direction of energy transfer and propagation of the wave
  • Longitudinal Waves: waves whose particles oscillate parallel to the direction of energy transfer and propagation of the wave

Describing Waves

    Properties of Waves

  • Amplitude (x0): the maximum distance of points on a wave from the equilibrium position
  • Wavelength (λ): the distance between two adjacent similar points (e.g. two adjacent crests) on a wave
  • Time Period (T): the time it takes for one complete wave to travel past a point
  • Frequency (f): the number of waves per second that travel past a point

    Properties of Transverse Waves

  • Crests: points of a transverse wave where the particles have the greatest positive displacement
  • Troughs: points of a transverse wave where the particles have the greatest negative displacement

    Properties of Longitudinal Waves

  • Compressions: areas of a longitudinal wave where the particles have the highest density
  • Rarefactions: areas of a longitudinal wave where the particles have the lowest density

Graphs of Waves

    Distance vs Displacement Graphs

  • Can represent both longitudinal and transverse waves, where you cannot tell them apart unless the y-axis is labelled with a direction
  • Longitudinal Waves: x-axis position stays constant
  • Transverse Waves: x-axis position changes slightly because particles move back and forth (net x-displacement is still 0)
  • Can be used to find the wavelength

    Distance vs Time Graphs

  • Can represent both longitudinal and transverse waves, where it is impossible to tell them apart
  • Can be used to find the time period

Wave Speeds

  • The speed of a wave is its wavelength divided by its time period: v = λ/T or v = λf
  • Speed of sound in air: approximately 330 metres per second
  • Speed of sound in water: approximately 1450 metres per second
  • Speed of light in a vacuum (c): approximately 300,000,000 metres per second

Sound Waves

  • They are mechanical waves
  • They are longitudinal waves
  • Compressions occur when air particles are closer together
  • Rarefactions occur When air particles are farther apart

Electromagnetic Waves

  • They are non-mechanical waves and do not need a medium to travel through
  • They consist of oscillations in the electric and magnetic fields that exist throughout the universe
  • The magnetic and electrical oscillations are perpendicular to one another
  • They travel at the speed of light (c)

Electromagnetic Spectrum

  • Energy is proportional to the waves' intensity, and hence to the square of their amplitude
  • Wavelength and frequency are related to the speed of light: c = λf
  • Gamma rays have the shortest wavelengths, and highest frequencies
  • Radio waves have the longest wavelengths, and lowest frequencies