Waves Basics

• Waves


  Transfer energy from one place to another but they don't transfer any matter
• Waves


  • Vibrate or oscillate
  • Can be interpreted as meaningful information
• Displacement


  How far from the equilibrium point the wave has oscillated
• Amplitude


  The maximum displacement
• Wavelength


  The distance of one entire oscillation
• Crest


  The very top of a wave
• Trough


  The opposite of the crest
• Time period


  The time it takes for one complete oscillation
• Frequency


  The number of complete oscillations per second, measured in hertz
• Calculating frequency


  1 / time period
• Calculating time period


  1 / frequency
• Calculating wave speed


  Wavelength x frequency
• Transverse waves


  • Oscillations are perpendicular to the direction of energy transfer
  • Examples: electromagnetic waves, water waves, string waves
• Longitudinal waves


  • Oscillations are parallel to the direction of energy transfer
  • Examples: sound waves, seismic p-waves
• How waves can be reflected off a boundary

  1. Draw ray diagrams

  2. Understand different types of reflection including specular and diffuse
• Waves aren't always reflected when they arrive at a boundary between two materials or mediums
• What can happen when a wave arrives at a boundary

  • Wave might be absorbed by the material
  • Wave could be transmitted and pass through the material
  • Wave could be reflected off the surface
• Which of the three things happens depends on the wavelength of the wave involved and the properties of the two materials
• Ray diagram


  Used to show reflection taking place
• Ray diagram


  • Start at the boundary between the two materials
  • Draw the incoming ray of light with an arrow
  • Draw the normal (perpendicular line)
  • Measure the angle of incidence
  • Angle of incidence = angle of reflection
• Point of incidence


  The point where the incoming ray touches the boundary
• Specular reflection


  Reflection from a perfectly smooth surface, where all the normals are in the same direction so the light is reflected in the same direction
• Diffuse/scattered reflection


  Reflection from a rough surface, where the normals point in different directions so the light is reflected in all different directions
• In both specular and diffuse reflection, the angle of incidence is always equal to the angle of reflection
• The surface of a rough material isn't flat, so the normals will be pointing in different directions, causing the reflected rays to get scattered
• Refraction of light waves


  When waves change direction as they pass from one medium to another, like from air into glass
• Refraction


  • Waves travel at different speeds in different materials or mediums
  • This happens because different mediums have different densities
  • Electromagnetic waves like light - the higher the density of the material, the slower the wave will travel through it
• Refraction of waves


  1. Wave travels from a less dense medium to a more dense medium

  2. Wave slows down as it passes into the more dense medium

  3. If wave hits the boundary at an angle, it will be refracted

  4. Wave bends towards the normal (perpendicular line) when passing into a more dense medium
• Drawing ray diagrams for refraction

  1. Draw normal (perpendicular line) at point of incidence

  2. Incident ray would continue straight if no refraction

  3. Refracted ray is drawn about halfway towards the normal

  4. Repeat process for ray exiting the medium, but this time it bends away from the normal

  5. Add angle of incidence and angle of refraction
• Wave speed equation


  • Wave speed = frequency x wavelength
  • Frequency stays the same, only wavelength changes
• Wave speed increases


  Wavelength increases
• Wave speed decreases


  Wavelength decreases
• Triangular prism


  • Different wavelengths of light are refracted by different amounts
  • This causes white light to spread out into a rainbow when passed through a prism
• Wavelength and frequency


  Inversely related - as one increases, the other decreases
• Color filters


  Only transmit certain wavelengths of light while absorbing the rest
• Primary color filters


  • Only allow one of the three primary colors (red, green, blue) to be transmitted
• Non-primary color filters


  • Transmit wavelengths of the same color as the filter, as well as wavelengths of primary colors that combine to make that color
• Seismic waves


  • Waves that spread out in every direction and travel through the different layers of the earth when large-scale events like volcanoes, earthquakes and explosions occur
• P waves


  Longitudinal waves that can travel through both solids and liquids
• S waves


  Transverse waves that only travel through solids