Waves

1
Waves
2
The Nature of a Wave

• A wave is a rhythmic disturbance that carries
  energy through matter and space.
• A wave pulse is a single disturbance that travels
  through a medium.
• A continuous traveling wave is a repeating and
  periodic disturbance which moves through a medium.

3
The source of all wave motion is a

1. movement of matter
2. harmonic object
3. vibration
4. amplitude

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Waves are the transfer of

1. energy
2. matter
3. vibrations
4. water

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What is a medium?

• A medium is a substance or material which carries
  the wave.
• The wave medium is not the wave and doesnt make
  the wave it merely carries or transports the
  wave from its source to another location.

6
A trumpet player is in the band room practicing
his music for the half-time show. What is the
medium which carries the sound wave?

1. The trumpet
2. The music he is producing
3. The air in the room
4. There is no medium

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Types of Waves

• Mechanical waves
• Electromagnetic waves
• Matter wave

8
Mechanical waves

• Mechanical waves require a material medium
• Newtons laws govern the motion of mechanical
  waves
• The speed of mechanical waves depends on the
  temperature of the medium
• Examples of mechanical waves include water
  waves, sound waves, and waves that travel along a
  rope or spring

9
Electromagnetic waves

• No medium is needed for the motion of
  electromagnetic waves
• All electromagnetic waves travel at a speed of
  2.9979 x 108 m/s in a vacuum.
• The details of electromagnetic waves cannot be
  observed directly
• Examples of electromagnetic waves include light
  waves, radio waves, microwaves, and X-rays

10
Electromagnetic Spectrum
11
Which of the following electromagnetic waves
travel the fastest at room temp?

1. Radio
2. Microwave
3. X-rays
4. None of the above

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Which of the following is NOT an electromagnetic
wave?

1. Radio
2. Sound
3. Light
4. X-fays

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Matter waves

• Electrons and other particles show wave-like
  behavior under certain conditions.
• Quantum mechanics is needed to describe the
  properties of matter waves.

14
The type of wave that does not require a medium
is a(n)

1. electromagnetic wave
2. mechanical wave
3. matter wave
4. All waves require a medium

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The type of wave that travels at 3.0 x 108 m/s
is a(n)

1. electromagnetic wave
2. mechanical wave
3. matter wave
4. All waves travel at this speed

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This type of wave is governed by Newtons laws of
motion.

1. Electromagnetic wave
2. Mechanical wave
3. Matter wave
4. All types of waves

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The properties of this type of wave are described
by quantum mechanics.

1. Electromagnetic waves
2. Mechanical waves
3. Matter waves
4. All types of waves.

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Sound is an example of this type of wave.

1. Electromagnetic
2. Mechanical
3. Matter
4. All of the above

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Light is an example of this type of wave.

1. Electromagnetic
2. Mechanical
3. Matter
4. All of the above

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Types of Mechanical Waves

• Transverse waves
• Longitudinal or compressional waves
• Surface waves

21
Transverse waves

• A transverse wave causes the particles of the
  medium to vibrate perpendicularly to the
  direction of the motion of the wave.
• The highest point of a transverse wave is called
  a crest.
• The lowest point of a transverse wave is called a
  trough.
• Examples of transverse waves include waves in
  piano and guitar strings

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Transverse Waves
23
Longitudinal waves

• A longitudinal wave causes the particles of a
  medium to move parallel to the direction of the
  motion of the wave.
• The point in which the medium is compressed
  (pressure is increased) is called the
  compression.
• The point in which the pressure in a medium is
  lowered is called the rarefaction.
• Examples of longitudinal waves include sound
  waves

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Longitudinal Waves
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Surface waves

• Surface waves are a mixture of transverse and
  longitudinal waves
• The particles in the medium move both parallel
  and perpendicular to the direction of the wave
• Examples of surface waves include water at the
  surface of the ocean

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Surface Waves
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A sound wave is an example of a ___ wave.

1. longitudinal
2. transverse
3. standing
4. constructive

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A mechanical wave in which the vibration of the
individual particles are perpendicular to the
direction of the wave is called a ___ wave.

1. longitudinal
2. sound
3. transverse
4. compression

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Measuring a Wave

• Wavelength (?)- The shortest distance between
  points where the wave pattern repeats itself.
  (Measured in units of length).
• Frequency (f)- The number of complete vibrations
  per second measured at a fixed location.
  (Measured in hertz-Hz)
• Period (T)-The shortest time interval in which
  the motion repeats itself (Measured in seconds)
• Amplitude- The maximum displacement from the rest
  or equilibrium position. A wave with a larger
  amplitude transfers more energy.

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Measuring a Wave
31
Relationships between wave properties

• Wavelength and frequency are inversely related.
  As wavelength increases, frequency decreases.
• Frequency and period are inversely related.
  (f1/T or T1/f)
• The velocity of a wave is equal to the distance
  it can travel in a given time period. vd/t or
  v?/T or v?f

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The time needed for a wave to make one complete
cycle is its

1. frequency
2. period
3. wavelength
4. amplitude

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33
The amplitude of a wave is 1 meter. The top-to
bottom distance of the disturbance is

1. 0.5 m
2. 1 m
3. 2 m
4. None of the above

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If you double the frequency of a vibrating
object, its period

1. doubles
2. halves
3. is quartered

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During a single period, the distance traveled by
a wave is

1. one-half wavelength
2. one wavelength
3. two wavelengths

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Wave Behavior

• The speed of a wave depends only on the
  properties of the medium it passes through, not
  on the waves amplitude.
• For example the speed of the slinky did not
  change when you increased the amplitude-only when
  you increased the length.
• As the tension of the spring increases, the speed
  of the wave increases.

37
Waves at Boundaries

• The wave that strikes a boundary is called the
  incident wave.
• The wave that returns after striking a boundary
  is called the reflected wave.
• If the boundary is fixed (like a rigid wall), the
  reflected wave has the same amplitude as the
  incident wave but is inverted (downward).
• http//www2.biglobe.ne.jp/norimari/science/JavaEd
  /e-wave6.html
• If the boundary is flexible (like a spring), the
  reflected wave is upward (erect) and is only
  partially reflected (amplitude is smaller). Part
  of the wave is also transmitted.
• http//paws.kettering.edu/drussell/Demos/reflect/
  reflect.html

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When a wave encounters a boundary, the wave that
strikes the boundary is called the

1. incident wave
2. reflected wave
3. refracted wave
4. normal wave

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When a wave encounters a boundary, the wave that
returns is called the

1. incident wave
2. reflected wave
3. refracted wave
4. normal wave

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40
When a wave is sent down a spring connected to a
wall, ___of the energy in the wave is reflected
back.

1. all
2. none
3. some

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A pulse is sent along a spring that is attached
to the wall. The reflected pulse is

1. inverted with equal amplitude
2. inverted with a smaller amplitude
3. upright with equal amplitude
4. upright with a smaller amplitude

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Superposition of Waves

• When two waves exist in the same place in the
  medium at the same time, each wave affects the
  medium independently.
• The displacement of a medium caused by two or
  more waves is the algebraic sum of the
  displacements caused by the individual waves.
  This is called the Principle of Superposition.

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Interference

• The result of superposition is called
  interference.
• Destructive interference occurs when waves have
  equal but opposite amplitudes.
• When the pulses meet and are in the same
  location, the displacement is zero.
• This point (which doesnt move at all) is called
  the node.
• The waves pass through each other unchanged.
• http//www2.biglobe.ne.jp/norimari/science/JavaEd
  /e-wave3.html

44
Interference (continued)

• Constructive interference occurs when the wave
  displacements are in the same direction.
• The result is an amplitude that is greater than
  any of the individual waves.
• A large pulse appears at the point where the two
  waves meet.
• This point has the largest displacement and is
  called the antinode.
• The waves pass through each other without
  changing their shapes or sizes.
• http//www2.biglobe.ne.jp/norimari/science/JavaEd
  /e-wave2.html
• http//www.sciencejoywagon.com/explrsci/media/inte
  rfer.htm

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___ occurs when two or more waves move through a
medium at the same time.

1. Refraction
2. Reflection
3. Interference
4. Resonance

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In destructive interference, a point that
experiences no displacement is called a

1. crest
2. trough
3. node
4. antinode

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Standing Waves

• A standing wave is a wave that appears to be
  standing still.
• Standing waves result from the interference
  between the incident wave and the reflected wave.
• As the frequency of the vibrations is increased,
  the number of nodes and antinodes increases. (see
  figure 14-14 on page 389)
• http//www2.biglobe.ne.jp/norimari/science/JavaEd
  /e-wave5.html
• http//www2.biglobe.ne.jp/norimari/science/JavaEd
  /e-wave4.html

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Waves in Two Dimensions

• Reflection occurs when a wave changes direction
  after striking a barrier.
• Ray diagrams model the movement of waves. A ray
  is a line drawn at right angles to the crests of
  waves.
• The incident ray is the ray pointing toward the
  barrier.
• The reflected ray is the ray pointing away from
  the barrier.
• The barrier is represented by a line.
• The normal is a line drawn perpendicular to the
  barrier.

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Ray Diagram of Wave
Angle of reflection
Normal
Angle of incidence
Angle of incidence
Normal
Angle of reflection
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Law of Reflection

• The law of reflection states that the angle of
  incidence is equal to the angle of reflection.
• The angle of incidence is the angle between the
  normal and the incident ray.
• The angle of reflection is the angle between the
  normal and the reflected ray.

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Refraction

• The change in direction of waves at the boundary
  between two media is called refraction.
• When crossing a boundary into a different medium,
  the wavelength decreases however, the frequency
  remains the same. Because there is a decrease in
  wavelength, the velocity also decreases.
• The change in velocity causes a change in
  direction. (see page 391)

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Refraction
53
Diffraction

• Diffraction is the spreading of waves around the
  edge of a barrier. Diffraction also occurs when
  waves meet an obstacle and bend around it,
  producing waves behind it.
• The smaller the wavelength, the less the
  diffraction.

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Diffraction
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Doppler Effect

• The Doppler effect is the change in the apparent
  frequency of a wave due to the motion of either
  the observer or the source of the wave.

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An incident light wave strikes a mirror at a 35o
angle with the surface of the mirror. What is
the angle of reflection?

1. 35o
2. 55o
3. 65o
4. 90o

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___ refers to the bending of waves as the waves
pass through different mediums resulting in a
change in speed of the wave.

1. diffraction
2. reflection
3. refraction
4. interference

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___ refers to waves that bend around the edge of
a barrier due to the dragging as the waves move
through the opening.

1. diffraction
2. reflection
3. refraction
4. interference

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Rainbows are an example of the ___ of light.

1. diffraction
2. refraction
3. reflection
4. interference

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An echo is an example of the ___ of sound.

1. diffraction
2. reflection
3. refraction
4. interference

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