wph12

• Displacement


  The distance of a particular point on a wave from its rest position
• Amplitude


  The magnitude of the maximum displacement from the rest position
• Frequency


  The number of complete wave cycles per second
• Time period


  The time for one complete oscillation of a wave
• Frequency


  Equal to 1 divided by the time period
• Wave speed


  The rate of movement of the wave
• Wavelength


  The distance from a peak to the next peak on a wave
• Longitudinal waves


  • Particles oscillate back and forth in the same direction as energy transfer
  • Examples: sound, ultrasound
• Transverse waves


  • Oscillations are perpendicular to the direction of energy transfer
  • Oscillations could be in electric/magnetic fields
• Measuring speed of sound


  1. Use loudspeaker and two microphones

  2. Measure time difference between microphone signals

  3. Use speed = distance/time to calculate speed
• Wave fronts


  Positions where all parts of the wave are in the same phase
• Coherence


  Waves have the same frequency and constant phase difference
• Phase difference


  The difference in the part of the wave cycle that two waves are in
• Path difference


  The difference in distance travelled by two waves
• Superposition of waves


  • Waves add/cancel depending on phase difference
• Standing/stationary waves


  Waves that store energy rather than transfer it, formed by interference of coherent waves
• Nodes


  Points of zero displacement in a standing wave
• Antinodes


  Points of maximum displacement in a standing wave
• Determining speed of waves on a string


  Use equation v = sqrt(T/μ) where T is tension and μ is mass per unit length
• Intensity


  Power per unit area of a wave
• Refraction


  Change in direction of a wave as it passes from one medium to another
• Intensity


  The amount of energy transferred per second per unit area
• Refraction


  The change in direction of a wave as it passes from one medium to another
• Refraction


  1. Light enters a new medium

  2. Light slows down

  3. Light changes direction
• Angle of incidence


  The angle between the incident ray and the normal
• Angle of refraction


  The angle between the refracted ray and the normal
• Refractive index


  The ratio of the speed of light in a vacuum to the speed of light in the medium
• Measuring refractive index


  1. Measure angles of incidence and refraction

  2. Plot graph of sin(i) vs sin(r)

  3. Gradient is the refractive index
• Critical angle


  The angle of incidence at which the angle of refraction is 90 degrees
• Total internal reflection


  The complete reflection of a wave at the boundary between two media when the angle of incidence is greater than the critical angle
• Polarization


  The restriction of the vibrations of a wave to a single plane
• Polarization


  1. Unpolarized light

  2. Pass through a filter

  3. Oscillations restricted to one plane
• Diffraction


  The spreading of waves around the edges of an obstacle or through an aperture
• Diffraction


  • Maximum when wavelength ≈ gap size
  • Explained by Huygens' principle
• Diffraction grating


  An optical component with a periodic structure that splits and diffracts light into several beams travelling in different directions
• Using a diffraction grating


  1. Measure distances

  2. Use trigonometry

  3. Calculate wavelength
• Pulse-echo technique


  Using a pulse of sound or ultrasound to measure distance to an object by timing the reflection
• The pulse-echo technique is used in medical scanning
• Detecting cracks in pipes

  1. Send signal down pipe

  2. Detect reflections at crack

  3. Determine location of crack
• Pulse echo technique


  1. Emit pulse

  2. Pulse reflects off object

  3. Receive reflected pulse

  4. Measure time between pulse and reflection

  5. Calculate distance to object