Topic 6 (waves)

• Wave

  Something that transfers energy and information through motion without the medium moving
• Types of waves

  • Mechanical wave
  • Electromagnetic wave
• Transverse waves

  • Oscillations are perpendicular to the direction of energy transfer
• Longitudinal waves

  • Oscillations are parallel to the direction of energy transfer
• Wavelength


  The distance between two consecutive peaks or troughs in a wave
• Frequency


  The number of oscillations per second
• Wavelength and frequency


  Wave speed = wavelength x frequency
• The wavelength is the distance between two consecutive peaks or troughs in a wave
• Frequency is the number of oscillations per second
• Wave speed = wavelength x frequency
• Wave speed


  Velocity at which a wave propagates
• Frequency


  Number of wave cycles per unit of time
• Wave speed


  Inversely proportional to frequency
• Wave speed = 1 / frequency
• When light travels from less dense to more dense medium, it slows down
• Wavefront


  • Imaginary line connecting points in a wave that are in phase
• All waves in the same medium refract at the same angle
• Slower waves have shorter wavelength
• Sound waves can only move through media, they cannot move through a vacuum
• Sound waves can be reflected and refracted
• Ultrasound


  Sound waves with frequencies above the human hearing range
• Ultrasound is safer than X-rays
• Using a Ripple Tank to calculate Wave Speed, Wavelength and Frequency


  1. Set up ripple tank

  2. Adjust water depth

  3. Switch on wave generator

  4. Measure length of waves

  5. Count number of waves passing a point in 10s

  6. Calculate wave speed, frequency and wavelength
• Using a Solid (String) to calculate Wave Speed, Frequency and Wavelength

  1. Attach string to vibration generator and pulley

  2. Place wooden bridge under string

  3. Switch on generator and adjust bridge

  4. Measure length of half wavelengths

  5. Calculate frequency from power supply

  6. Calculate wave speed using frequency and wavelength
• Seismic waves


  Primary waves mov are longitudinal <|>Secondary waves are transverse
• Seismic wave types


  • Primary
  • Secondary
• Primary waves travel faster than secondary waves</b>
• Primary waves can travel through solid or liquid</b>
• Secondary waves can only travel through solid</b>
• Earthquakes generate seismic waves
• Earthquake focus


  • Point where earthquake originates
• Earthquake epicentre


  • Nearest point to focus on surface
• Seismic waves are recorded by seismometers
• shadow zone = where no primary or secondary waves are detected
• Seismic waves are generated in the crust
• Electromagnetic (EM) waves


  Transverse waves
• Part of EM spectrum detected by human eyes

  Visible light
• Electromagnetic waves


  1. Transfer energy from source

  2. Form a continuous spectrum

  3. All types travel at same velocity through vacuum or air
• Types of EM waves

  • Radiowaves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma waves
• Radiowaves


  • Longest wavelength
  • Lowest frequency
  • Least energy