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Waves

  • A wave pulse is a disturbance that propagates (spreads) through a medium or space.
  • A periodic wave is a regularly repeating series of wave pulses
  • The direction of propagation is the direction the wave is moving or spreading

2 Wave types

  • Mechanical
  • require a medium to be transmitted
  • the majority of waves
  • Electromagnetic
  • do not require a medium, can travel in a vacuum
  • all of these are part of the electromagnetic spectrum of light

Wave classes

  • Waves can be classified by the way the wave vibrates with respect to the direction it is moving.
  • Transverse waves vibrate perpendicular to the direction of motion
  • Longitudinal waves vibrate parallel to the direction of motion
  • Torsional waves twist & change their axis of vibration

Other wave classes

  • Water waves get special classifications
  • Circular Waves - The waves propagate outward in circles from a central source
  • Planar waves - parallel wave fronts
  • The surface of the wave appears transverse.
  • The wave propagates through longitudinal compression.

Wave Characteristics

  • Crest the highest peak of a transverse wave
  • Trough the lowest point of a transverse wave
  • Amplitude - The distance from a crest to the equilibrium position, it is directly proportional to the energy of the wave.
  • compression a location where the molecules of a longitudinal wave are the closest together ( ~ crest)
  • rarefaction a location where the molecules of a longitudinal wave are the farthest apart (~ trough)
  • Wavelength - the distance between two consecutive crests for a transverse wave, or two consecutive compressions for a longitudinal wave.
  • Period - the time required for two consecutive crests to pass a given point in a transverse wave (compression/longitudinal)
  • Frequency - the number of crests passing a given point in a unit of time (seconds) - measured in Hertz (Hz)

Wave Equations

  • Period = 1/Frequency
  • T = 1/f
  • Speed of propagation = frequency x wavelength
  • v = f l

Rectilinear Propagation

  • Continuous waves travelling in a uniform medium propagate in straight lines perpendicular to the wave front.

Reflection

  • A wave is turned back when it encounters a barrier
  • The angle of incidence equals the angle of reflection
  • Incident & reflected waves lie in the same plane

Reflection & Inversion

  • When a wave is reflected from a more dense or fixed boundary, the reflected wave undergoes a 180 degree phase change or inversion.
  • When a wave is reflected from a less dense or free end, the reflected wave undergoes no phase change or inversion.

Refraction

  • The change in speed of a wave as it passes from one medium to another causes an apparent bending of the path of the wave.
  • At any boundary between media - some of the wave energy is reflected and some is refracted.

http://www.physics.gatech.edu/academics/tutorial/phys2121/Java%20Applets/ntnujava/propagation/propagation.html

 

Diffraction

  • The spreading of a wave disturbance beyond the edge of a barrier

Interference

  • Whenever two waves meet, they produce a resultant displacement that is the vector sum of the individual displacements.
  • Constructive interference produces a wave greater than the initial wave.
  • Destructive interference produces a wave smaller than the initial wave.

Superposition

  • Two waves can be added graphically or algebraically.
  • sinx + sinx = 2 sinx sinx + -sinx = 0

Standing waves

  • When two periodic waves of the same amplitude and wavelengths travelling in opposite directions interfere, they create a standing wave pattern.
  • Node - region of zero displacement
  • Antinode - region of maximum displacement

Online Resources and Tutorials

http://www.physicsclassroom.com/Class/waves/wavestoc.html

Classwork & Homework

  • Classwork
  • Read Modern Physics p.222-232
  • Finish Answering Questions #1-14
  • Solve problems #1-5
  • Homework
  • Complete WS 25-1, 25-2
  • Classwork
  • Read p.233-249
  • Answer Questions #1-5, 7-10, 12-16
  • Solve problems #2,4
  • Homework
  • Worksheet 25-3, WS 15

 

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