Waves and Sound

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Waves and Sound

• Wave Characteristics

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Transferring Energy Without Transferring Matter

• Vibrating bodies connected to their environment
  will transfer energy to the environment.
• The vibrations are then transferred though the
  environment from neighbor to neighbor.
• This energy transfer is called wave motion.
• Wave motion moves energy through a medium without
  moving the whole medium.
• Only the shape or form of wave travels, not the
  medium.

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Definition of wave

• A periodic disturbance which travels through a
  medium from one point in space to the others.

Wave motion means the propagation of waves
through a medium.
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TYPES OF WAVESWaves are classified into
different types according to their natures
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Three types of waves

• Mechanical waves require a material medium to
  travel (air, water, ropes).
• Electromagnetic waves do not require a medium to
  travel (light, radio).
• Matter waves are produced by electrons and
  particles.

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Electromagnetic Waves

• Material medium is not essential for propagation.
  e/m waves travel through vacuum.
• Disturbance of electric and magnetic fields
  traveling through space.
• All electromagnetic waves are transverse waves.

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Electromagnetic Waves

• Light Waves
• Radio Waves
• X-Rays

• No Medium Required
• Travels At The Speed Of Light
• 3 X 108 m/s in a vacuum
• Cannot Be Observed

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Matter Waves

• Matter is in the form of particles.
• Energy is in the form of waves.
• Energy can be quantized and matter can have a
  wavelength.
• Matter displays wavelike properties.

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Mechanical Waves

• Transverse waves cause the medium to move
  perpendicular to the direction of the wave.
• Longitudinal waves cause the medium to move
  parallel to the direction of the wave.
• Surface waves are both transverse waves and
  longitudinal waves mixed in one medium. (Such as
  water waves)
• Torsional waves produce a twisting motion through
  the medium such as the ones which caused the
  collapse of the Tacoma Narrows Bridge.

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3 Types of Mechanical Waves
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Transverse Wave
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Transverse Waves

• These waves cause particles of a medium to
  vibrate perpendicular to the direction of motion
• The waveform appears in the shape of sine curve.

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Longitudinal Waves

• These waves cause medium to vibrate in a
  direction parallel to the direction of motion.

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Longitudinal Waves

• Speaker membrane expands, creating a region where
  the air molecules are packed closely together, a
  "condensation".  The air pressure in a
  condensation is higher than normal.
• As the membrane moves back, a regionis left
  behind where few molecules are located, a
  "rarefaction".  Meanwhile, thecondensation moves
  forward.

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Surface Waves

• Waves out on the ocean's surface are a
  combination of transverse and longitudinal waves.
  
• The wave height is the distance from a trough to
  a peak and the wavelength is the peak to peak
  distance.
• When the wave height is
  1/7 the wavelength
  the wave breaks.

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Tacoma Narrows BridgeTorsional Oscillation
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Period T Frequency f

• The PERIOD is the time for a particle of the
  medium to complete one oscillation.
• The SI unit for period is the second

• The FREQUENCY of is the number of cycles per unit
  time.
• The frequency of a wave is equal to the number of
  waves that pass a particular point in one second.
• The unit is Hertz (Hz) which is a cycle per
  second.
• FREQUENCY is also the reciprocal of the period.

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Period and Frequency
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Amplitude A

• The AMPLITUDE of a wave is the maximum distance
  of a particle from the equilibrium position.
• The SI unit for amplitude is meter

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Amplitude A

• The energy content of a wave is indicated by the
  amplitude.
• Two waves of the same frequency can have
  different amplitudes.
• The greater the amplitude, the more work a wave
  can do.
• Amplitude does not affect wavelength, frequency
  or velocity

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Wavelength ?

• The WAVELENGTH of a wave is the length of one
  complete cycle.
• It is the distance between two consecutive in
  phase points.
• In phase points are those that are moving in step
  with each other.

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Comparing waves
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Wave Velocity

• The speed of a wave is the product of the waves
  frequency and wavelength.
• The speed does not depend on amplitude or
  frequencyit depends on the properties of the
  medium.
• Sound waves depend on temperature of the air and
  water waves depend on depth of water.

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Do you remember..?

• 4. The periodic wave in the diagram below has a
  frequency of 40. hertz.
• What is the speed of the wave?
• a. 13 m/s b. 60. m/s c. 27 m/s d.
  120 m/s

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More to remember..

• Austin drops a stone into a dry well 175 m deep.
  How long, after he drops the stone, does he hear
  it hit the bottom of the shaft?
• The speed of sound waves is 340 m/s.
• Assume g 10 m/s/s

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Warm up

• Sitting on the beach I notice the waves motion .
  I see a crest pass me every 2 seconds. The crests
  are
• 3 meters apart. What is the waves velocity?

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Waves and Sound

• Wave Actions

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Waves and Boundaries

• When a wave encounters an interface (boundary),
  it may be reflected and/or transmitted!
• An incident wave goes into a new medium as a
  transmitted wave and bounces back as a reflected
  wave.
• Density difference determines how much of the
  wave is transmitted and how much is reflected.

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Waves and Boundaries

• Small Difference Between the Densities of the two
  Media
• Most of wave is transmitted.
• Amplitude of transmitted wave will be greater
  than amplitude of reflected wave.
• Large Difference Between the Densities of the two
  Media
• Most of incident wave is reflected.
• Amplitude of reflected wave is greater than
  amplitude of transmitted wave.

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Less Dense to More Dense Medium

• When a wave hits the boundary of a more dense
  medium, the reflected wave is inverted.

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More dense to a Less Dense Medium

• When a wave hits the boundary of a less dense
  medium, the reflected wave is erect.

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Reflection of Waves

• A traveling wave is reflected when it hits a
  barrier.
• This phenomenon can easily be observed when a
  traveling water wave hits a reflector in the
  ripple tank.

Reflector
Reflected waves
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Law of Reflection

• When an incident wave encounters a boundary at an
  angle, ?, from the normal, its reflected wave
  will be reflected at the same angle from the
  normal.

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Do you remember???

• What is a boundary?
• What determines the speed of a wave?
• What happens to a wave hitting a boundary?
• How do you know if a wave will reflect erect or
  inverted?
• What does not change at a boundary?
• What must change at a boundary?

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When a wave passes into a new medium

• Its wavelength changes
• Its speed changes with density
• Its frequency remains the same

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Refraction

• Refraction is the bending of a wave as it passes
  from one medium to another medium of different
  propagation speed.

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The Densities of the Media

• If the light passes from a less dense to a more
  dense medium, it bends toward the normal.
• If the light passes from a more dense to a less
  dense medium, it bends away from the normal.

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Refraction of Waves

• The speed of a water wave increases with depth.
• This change in speed is accompanied by
  refraction.

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Diffraction

• Diffraction is the spreading of a wave
  disturbance around and beyond the edge of a
  barrier.
• When a traveling water wave hits an obstacle, the
  wave fronts spreads out round the edge and
  becomes curved.
• The wavelength of the wave is not changed in
  diffraction.

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Superposition Principle

• Wave interference occurs when two or more waves
  act simultaneously on a medium.
• Whenever two or more waves pass through each
  other, the resulting disturbance at a given point
  in the medium may usually be found by adding the
  individual displacements that each wave would
  have caused. (Principle of Superposition)

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Principle of Superposition

• The displacement of a medium caused by two or
  more waves is the algebraic sum of the
  displacements caused by the individual waves.
• When colliding waves combine (add) the result can
  either be bigger or smaller than the original
  waves.
• The waves add constructively or destructively
  depending on the relative sign of each wave.

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Superposition Interference

• Consider two harmonic waves A and B meeting at x
  0.
• The displacement versus time for each is shown
  below

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Constructive Interference
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Constructive Interference

• Occurs when wave displacements are in phase.
• Two waves combine to create a larger wave.
• Constructive interference occurs when the waves
  are trying to displace the medium in the same
  direction.
• More than one wave can occupy the same space at
  the same time.

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Destructive Interference

• Occurs when wave displacements are opposite in
  phase.
• One wave cancels the other out.

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Destructive Interference

• When these two waves are completely overlapping,
  there will be complete destructive interference.
• Destructive interference occurs when the waves
  are trying to displace the medium in opposite
  directions.

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Before and AfterWaves have the ability to pass
through one another and not change.
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Waves Moving in and Out of Phase

• When the 2 waves are in phase, the resulting
  disturbance has a maximum amplitude.
• When the 2 waves are out of phase, the resulting
  disturbance has a minimum amplitude.

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Interference in Water Waves
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Standing Wave in Action

• Nodes are places on a standing wave that do not
  appear to move.
• Antinodes are places on a standing wave that are
  the greatest displacement from equilibrium.

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Standing Waves

• Waves traveling in opposite directions, with the
  same frequency, wavelength, and amplitude,
  produce a standing wave.