P6

• Waves transfer energy from one place to another but do not transfer matter
• Displacement

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


  Maximum displacement of a wave
• Wavelength

  Distance of one entire oscillation
• Trough


  The opposite of the crest
• Time period

  Time it takes for one complete oscillation
• Frequency

  Number of complete oscillations per second
• Frequency calculation

  Frequency = 1 / Time period
• Wave speed calculation

  Wave speed = Wavelength x Frequency
• Transverse waves

  Oscillations are perpendicular to the direction of energy transfer
• Examples of transverse waves

  Electromagnetic waves, ripples in water, waves on guitar strings
• Longitudinal waves

  Oscillations are parallel to the direction of energy transfer
• Examples of longitudinal waves

  Sound waves, seismic p waves
• Reflection of waves

  1. Waves can be reflected off a boundary

  2. Three things can happen when a wave arrives at a boundary: absorption, transmission, reflection

  3. Reflection depends on the wavelength of the wave and the properties of the materials involved
• Ray diagrams

  • Used to show reflection taking place
  • Angle of incidence is always equal to the angle of reflection
• Drawing a ray diagram

  1. Start at the boundary between the two materials

  2. Draw incoming ray of light

  3. Draw the normal (perpendicular line)

  4. Measure the angle of incidence

  5. Draw the reflected ray at the same angle from the normal

  6. Point of incidence is where the incoming ray touches the boundary
• Types of reflection

  • Specular reflection: from perfectly smooth surfaces, all reflected rays are in the same direction
  • Diffuse or scattered reflection: from rough surfaces, reflected rays are scattered in different directions
• Specular reflection gives a clear image like looking in a mirror
• Diffuse reflection scatters light in different directions, making it impossible to see a clear reflection
• Angle of incidence


  Is always equal to the angle of reflection
• Refraction of light waves

  Waves change direction as they pass from one medium to another like from air into glass
• Understanding refraction

  • Waves travel at different speeds in different materials or mediums due to different densities
  • Higher density of the material results in slower wave travel
  • When a wave travels from a less dense medium to a more dense medium, it slows down
  • Refraction occurs when a wave changes direction passing into a more dense medium
• When a wave passes from a less dense medium to a more dense medium

  It will slow down and bend towards the normal
• When a wave hits the boundary at an angle

  It will be refracted, changing its direction
• Drawing ray diagrams for refraction

  • Draw the normal perpendicular to the surface at the point of incidence
  • Incident ray slows down and bends towards the normal in a more dense medium
  • Refracted ray continues through the medium
  • Repeat the process for the emergent ray when passing from a more dense to a less dense medium
  • Add angle of incidence and angle of refraction to the diagram
• Change in wave speed during refraction

  • Frequency stays the same, but wavelength changes as speed changes
  • If speed increases, wavelength increases and vice versa
• Different wavelengths of light are refracted by different amounts
• White light through a triangular prism will spread out into different colors like a rainbow
• Electromagnetic waves

  1. They oscillate perpendicular to the direction of energy transfer

  2. They travel at the speed of three times ten to the eight meters per second in a vacuum

  3. They travel at different speeds in different mediums leading to refraction
• Types of electromagnetic waves

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Wavelength and frequency

  They are inversely related, if one goes up the other goes down
• Frequency and wavelength in the spectrum

  Frequency increases from left to right while wavelength decreases
• Colors of the rainbow

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet
• Order of waves in the spectrum

  Start with visible light in the middle and work your way outwards
• Order of waves in the spectrum

  • Visible light
  • Ultraviolet
  • X-ray
  • Gamma rays
  • Microwaves
  • Radio waves
• Ultraviolet, X-ray, and Gamma rays are ionizing and can cause damage to cells
• Microwaves and radio waves

  Used in communication and are on the far left of the spectrum
• Electromagnetic waves come from everywhere
• Gamma rays can be emitted from radioactive decay
• Visible light, ultraviolet, and x-rays can be emitted when electrons drop down energy levels