Waves

• Medium


  An elastic substance (like air or water) that allows for a transfer of energy
• Waves


  • The means that energy is transferred
  • Classified into two different types: mechanical waves and electromagnetic waves
• Mechanical waves


  Require an elastic medium to travel through (e.g. sound waves)
• Electromagnetic waves


  Do not require a medium to travel through (e.g. light waves) and they travel at the speed of light
• Creating a wave


  1. Disturbance in a medium

  2. Wave continues outward until it runs out of energy
• Amplitude


  The greatest (furthest) distance that a particle travels from its point of rest (equilibrium)
• Displacement


  The distance between a particle's position and the equilibrium
• Equilibrium


  The natural resting position assumed by the particles in a medium
• Sound waves


  Longitudinal waves (compression waves) producing rarefaction and compressions
• Sound waves


  • Require a medium to travel through because it is a mechanical wave
• Transverse waves


  • Particles move at right angles to the direction of propagation of the wave
  • Direction of oscillation of the particles is perpendicular (90 degrees) to the direction of energy transfer

  
• Speed of sound


  Mediums of different densities will transmit sound waves at different speeds. Atmospheric conditions also affect the speed like temperature, humidity and air movement.
• Longitudinal (compression) waves


  • Particles move in the same direction as the pulse moves
  • Direction of oscillation of the particles is parallel to the direction of energy transfer
  • Compression is the part where particles are closest together
  • Rarefaction is the part where particles are furthest apart

  
• Pulse


  A singular disturbance to create a movement
• Wavelength


  The minimum distance between two points on the wave in phase (measured as a distance and described using a Greek letter λ)

  
• Phase


  A position of a particle in a cycle that has the same velocity and amplitude. Particles in phase have the same motion.
• Crest


  The highest point of a wave (maximum positive displacement)
• Trough


  The lowest point of a wave (maximum negative displacement)
• Frequency


  The number of waves passing a given point per second, measured in Hertz (Hz)

  
• Period


  The time it takes for one full wave (one wavelength) to pass a point
• Determining wave speed


  Using the wave equation: v = f * λ

  
• Displacement-distance graphs


  • Allow the displacement (amplitude) and wavelength to be determined

  
• Displacement-time graphs


  • Show the position of the wave and also the position of a single point on the wave at certain times

  
• Wave speed


  Depends on the medium that it is moving through

  
• Reflection


  When an incident wave reaches a boundary and changes direction returning into the same medium

  
• Transmission


  The passage of a wave from one medium to another

  
• Reflection in one dimension

  • Considers the movement of particles in only one direction
  • Reflected waves have approximately the same amplitude
  • Fixed end is out of phase by 180°, free end has no phase change

  
• Temperature increases


  Speed of sound increases at approximately 0.6ms-1 per degree
• Reflection at a boundary

  • Considers a change in media
  • More to less (heavy to light)
  • Less to more (light to heavy)
• Reflection of waves in two-dimensions

  
• Reflection in one dimension

  1. Energy arrives at a medium and bounces back

  2. Wave is sent down a spring attached to a wall

  3. Fixed end is out of phase by 180°

  4. Free end has no phase change
• Boundary


  A change between two different media
• Temperature


  Affects the frequency of the standing waves produced for sound (from musical instruments)
• If details of the speed of sound is not listed, assume that it is 340ms-1
• All properties for waves apply to sound (reflection, refraction and diffraction) including the wave equation
• Calculating wavelength of a musical note

  Given: frequency of 261.6 Hz, temperature of 25 degrees
• Calculating speed of a sound wave

  Given: frequency of 800 Hz, wavelength of 42 cm
• Reflection at a boundary

  1. Wave moves from heavy to light medium

  2. Wave moves from light to heavy medium

  
• Calculating time for sound to reach teacher

  Given: frequency of 1000 Hz, distance of 3.0 m
• Wavelength


  For a sound with frequency of 1000 Hz