(3.1) Progressive and Stationary Waves

• What is a progressive wave?

  A wave that transfers energy without material
• How do water waves behave?

  Water particles move up and down
• What is amplitude in a wave?

  Maximum displacement from equilibrium
• What are the units of amplitude?

  Metres (m)
• What does frequency, f, measure?

  Complete oscillations per second
• What are the units of frequency?

  Hertz (Hz)
• What are the units of wavelength?

  Metres (m)
• What is wavelength, λ?

  Length of one whole oscillation
• What does speed, c, represent in waves?

  Distance travelled per unit time
• What are the units of wave speed?

  Metres per second (m/s)
• What does phase indicate in a wave?

  Position on a wave cycle
• What are the units of phase?

  Radians, degrees, or fractions of a cycle
• What is phase difference?

  How much one wave lags behind another
• What are the units of phase difference?

  Radians, degrees, or fractions of a cycle
• What does period, T, measure?

  Time taken for one full oscillation
• What are the units of period?

  Seconds (s)
• When are two points on a wave in phase?

  When they are at the same point in the cycle
• What is the phase difference for points in phase?

  A multiple of 360° (2π radians)
• What does it mean for two points to be completely out of phase?

  They are an odd integer of half cycles apart
• What is the formula for wave speed?

  c = fλ
• What is the formula for frequency?

  f = 1/T
• What characterizes transverse waves?

  Particles oscillate at right angles to energy transfer
• What type of waves are electromagnetic waves?

  Transverse waves
• What is the speed of electromagnetic waves in a vacuum?

  3 x 10⁸ m/s
• How can transverse waves be demonstrated?

  By shaking a slinky vertically
• What characterizes longitudinal waves?

  Particles oscillate parallel to energy transfer
• What are compressions and rarefactions?

  Regions in longitudinal waves

  
• Why can't longitudinal waves travel in a vacuum?

  They require a medium to propagate
• How can longitudinal waves be demonstrated?

  By pushing a slinky horizontally
• What is a polarised wave?

  A wave oscillating in only one plane
• Which waves can be polarised?

  Only transverse waves
• Why does polarisation provide evidence for transverse waves?

  Oscillations are perpendicular to direction of travel
• What is the function of polaroid sunglasses?

  They reduce glare by blocking light
• How do polaroid sunglasses work?

  They allow oscillations in the plane of the filter
• What is an application of polarisation in communication?

  TV and radio signals use plane-polarisation
• How must the receiving aerial be aligned for TV and radio signals?

  In the same plane of polarisation
• What is superposition in wave theory?

  Combination of displacements of two waves

  
• What occurs during destructive interference?

  One wave has positive, the other negative displacement
• What are the two types of interference in superposition?

  Constructive and destructive interference
• What occurs during constructive interference?

  Waves have displacement in the same direction