Waves

• Longitudinal waves

  Particles in the wave vibrate back and forwards in the same direction that the energy is being transferred
• Transverse waves

  Particles in the wave move side to side and the energy is being transferred at 90 degrees
• Longitudinal waves

  • Sound
  • Ultrasound
• Transverse waves

  • Electromagnetic spectrum
  • Light
  • Water ripples
• Amplitude

  Distance between where the particle normally is and how far it vibrates up and down
• Wavelength

  Distance from a point on one wave to the equivalent point on the adjacent wave
• Frequency

  Number of waves passing a point each second, measured in Hertz
• Time period

  Time for one wave cycle, equal to 1 divided by the frequency, measured in seconds
• Measuring wave speed

  Distance between two points / Time taken for wave to travel between those points
• Waves approaching a material

  Can be reflected, absorbed or transmitted
• Angle of incidence

  Angle between incident ray and normal
• Angle of reflection

  Angle between reflected ray and normal
• Speed of sound in air is approximately 330 m/s at ground level
• How sound is detected by the human ear

  1. Air particles vibrate

  2. Vibrations pass to eardrum

  3. Eardrum vibrates

  4. Vibrations passed to fluid in inner ear

  5. Bones move and send electrical signal to brain
• Humans can only hear sound waves between 20 Hz and 20 kHz
• Ultrasound

  Sound waves with frequency greater than 20 kHz, which humans cannot hear
• Using ultrasound to detect cracks or objects

  1. Transducer sends ultrasound wave

  2. Wave partially reflected at boundary/crack

  3. Time taken for reflected wave to return measured

  4. Distance to obstruction calculated from speed and time
• Uses of ultrasound

  • Detecting cracks in pipes
  • Scanning babies in the womb
• Seismic waves

  Waves that travel through the Earth when there is an earthquake or other underground movement
• 1. waves

  Primary seismic waves, longitudinal, can travel through liquids and solids
• 1. waves

  Secondary seismic waves, transverse, cannot travel through liquids
• 1. waves can travel through the Earth's core, S-waves cannot
• The speed of light in a vacuum is 300,000 km/s
• Main categories of the electromagnetic spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Detecting earthquakes

  1. Primary waves detected

  2. Secondary waves detected

  3. Waves travel through earth

  4. Waves end up
• Electromagnetic spectrum

  A whole series of waves that all travel at the same speed through a vacuum, which is the speed of light (300,000 m/s)
• Main categories of electromagnetic waves

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• As you go through the electromagnetic spectrum

  Wavelength decreases, frequency increases
• Ionizing waves

  Higher frequency electromagnetic waves that are more dangerous
• Uses of electromagnetic waves

  • Radio - television, communication
  • Microwaves - communication, heating food
  • Infrared - heating, night vision
  • Visible light - fiber optic communication
  • Ultraviolet - energy efficient lamps, sun tanning
  • X-rays and gamma rays - medical uses
• Refraction

  When a wave changes direction when it meets a different medium, due to the change in speed
• Convex lens

  • Bulges in the middle
  • Makes light converge
• Concave lens

  • Dips in the middle
  • Makes light diverge
  • Forms a smaller, virtual image
• Magnification

  Ratio of image size to object size
• Color

  • Each color has its own frequency and wavelength
  • Filters only allow certain colors to pass through
  • Objects appear colored by reflecting certain colors and absorbing others
• Black body

  Absorbs all radiation landing on it, and emits radiation quickly
• Earth absorbing more energy than it emits

  Temperature is slowly rising, contributing to global warming and climate change