Waves

• Wavelength


  Distance between the same points on two consecutive waves

  
• Amplitude


  Distance from equilibrium line to the maximum displacement (crest or trough)
• Frequency


  The number of waves that pass a single point per second
• Period


  The time taken for a whole wave to completely pass a single point
• Wave velocity calculation

  Velocity = frequency × wavelength

  
• Period calculation

  Period = 1/frequency
• Increase frequency


  Velocity increases
• Wavelength increases


  Velocity increases
• Period

  Inversely proportional to frequency
• Smaller period

  Higher frequency, greater velocity
• Transverse waves

  • Have peaks and troughs
  • Vibrations are at right angles to the direction of travel

  
• Transverse waves


  • Light
  • Electromagnetic waves

  
• Longitudinal waves

  • Have compressions and rarefactions
  • Vibrations are in the same direction as the direction of travel

  
• Longitudinal waves

  • Sound waves

  
• For both types of waves, the wave moves and not whatever it passes through

  
• Measuring sound velocity in air

  1. Make a noise, record echo time

  2. Use two microphones, record time difference
• Measuring ripples on water surface

  1. Use a stroboscope

  2. Move a pencil along the paper
• Waves can be reflected, absorbed, or transmitted at the boundary between two different materials

  
• Reflection


  • Waves reflect off a flat surface
  • Smoother surfaces create stronger reflected waves
  • Rough surfaces scatter light

  
• Angle of incidence


  Angle of reflection

  
• Transmission


  • Waves pass through transparent material
  • More transparent, more light passes through
• Absorption

  • Light absorbed if frequency matches energy levels of electrons
  • Light reemitted as heat

  
• If a material appears green, only green light has been reflected
• Sound waves can travel through solids causing vibrations in the solid
• Sound wave transmission in the ear

  1. Outer ear collects sound

  2. Sound travels down ear canal

  3. Sound waves hit eardrum

  4. Eardrum vibrates

  5. Vibrations transmitted to fluid in inner ear
• Humans cannot hear below 20Hz or above 20kHz
• Higher frequencies cannot be heard as we get older
• Ultrasound is a sound wave with a frequency higher than 20kHz
• Infrasound is a sound wave with a frequency lower than 20Hz
• Ultrasound imaging

  1. Ultrasound reaches boundary

  2. Partially reflected back

  3. Receiver records reflected waves
• Radio waves are produced by oscillations in electrical circuits
• Atoms absorb or emit EM radiation when electrons change orbit
• Gamma rays originate from changes in the nucleus of an atom
• Hazards of radiation

  • UV light can cause skin cancer
  • X-rays and gamma rays can cause gene mutation
• Uses of EM waves

  • Radio - TV and radio
  • Micro - Satellite communication
  • IR - Cooking food
  • Visible - Fibre optics
  • UV - Sun tanning
  • X-ray - Medical imaging
• Concave lenses

  • Cave inward
  • Thinner at centre than at edges
  • Spreads light outwards
• Convex lenses

  • Wider at centre
  • Focus light inwards
• Each colour within the visible light spectrum has its own narrow band of wavelength and frequency
• Types of reflection

  • Specular - smooth surface gives a single reflection
  • Diffuse - rough surface causes scattering

  
• An opaque object has colour determined by the strength of reflection for different wavelengths