progressive waves

• a progressive wave carries energy from one place to another without transferring any material.

  a wave is caused by something making particles or fields oscillate at a source. these oscillations pass through the medium as the wave travels, carrying energy with it.
• examples of proof that waves carry energy:

  • electromagnetic waves cause things to heat up
  • x rays and gamma rays knock electrons out of their orbits, causing ionisation
  • loud sounds cause large oscillations of air particles which can make things vibrate
  • wave power can be used to generate electricity
• • cycle = one complete vibration of the wave
  • displacement (metres) = how far a point on the wave has moved from its undisturbed position
  • amplitude (metres) = maximum magnitude of displacement
  • wavelength (metres) = the length of one whole wave cycle, from crest to crest or trough to trough
• • period (seconds) = the time taken for a whole cycle to complete, or to pass a given point
  • frequency (hertz) = the number of cycles per second passing a given point
  • phase (degrees or radians or fractions of a cycle) = a measurement of the position of a certain point along the wave cycle
  • phase difference (degrees or radians or fractions of a cycle) = the amount one wave lags behind the other
• reflection = the wave is bounced back when it hits a boundary

  • reflection can be demonstrated in a ripple tank

  refraction = the wave changes speed as it enters a different medium, which results in the wave changing direction
• frequency of a wave is the inverse of the period
• wave equation:

  wave speed = wavelength x frequency