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

• movement of matter
• harmonic object
• vibration
• amplitude

4
Waves are the transfer of

• energy
• matter
• vibrations
• water

5
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?

• The trumpet
• The music he is producing
• The air in the room
• There is no medium

7
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
Matter waves

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

11
The type of wave that does not require a medium
is a(n)

• electromagnetic wave
• mechanical wave
• matter wave
• All waves require a medium

12
The type of wave that travels at 3.0 x 108 m/s
is a(n)

• electromagnetic wave
• mechanical wave
• matter wave
• All waves travel at this speed

13
This type of wave is governed by Newtons laws of
motion.

• Electromagnetic wave
• Mechanical wave
• Matter wave
• All types of waves

14
This properties of this type of wave are
described by quantum mechanics.

• Electromagnetic waves
• Mechanical waves
• Matter waves
• All types of waves.

15
Sound is an example of this type of wave.

• Electromagnetic
• Mechanical
• Matter
• All of the above

16
Light is an example of this type of wave.

• Electromagnetic
• Mechanical
• Matter
• All of the above

17
Types of Mechanical Waves

• Transverse waves
• Longitudinal or compressional waves
• Surface waves

18
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

19
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

20
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

21
A sound wave is an example of a ___ wave.

• longitudinal
• transverse
• standing
• constructive

22
A mechanical wave in which the vibration of the
individual particles are perpendicular to the
direction of the wave is called a ___ wave.

• longitudinal
• sound
• transverse
• compression

23
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.

24
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

25
The time needed for a wave to make one complete
cycle is its

• frequency
• period
• wavelength
• amplitude

26
The amplitude of a wave is 1 meter. The top-to
bottom distance of the disturbance is

• 0.5 m
• 1 m
• 2 m
• None of the above

27
If you double the frequency of a vibrating
object, its period

• doubles
• halves
• is quartered

28
During a single period, the distance traveled by
a wave is

• one-half wavelength
• one wavelength
• two wavelengths

29
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.

30
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.

31
When a wave encounters a boundary, the wave that
strikes the boundary is called the

• incident wave
• reflected wave
• refracted wave
• normal wave

32
When a wave encounters a boundary, the wave that
returns is called the

• incident wave
• reflected wave
• refracted wave
• normal wave

33
When a wave is sent down a spring connected to a
wall, ___of the energy in the wave is reflected
back.

• all
• none
• some

34
A pulse is sent along a spring that is attached
to the wall. The reflected pulse is

• inverted with equal amplitude
• inverted with a smaller amplitude
• upright with equal amplitude
• upright with a smaller amplitude

35
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.

36
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

37
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

38
___ occurs when two or more waves move through a
medium at the same time.

• Refraction
• Reflection
• Interference
• Resonance

39
In destructive interference, a point that
experiences no displacement is called a

• crest
• trough
• node
• antinode

40
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

41
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.

42
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.

43
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)
• http//www.sciencejoywagon.com/physicszone/otherpu
  b/wfendt/refraction.htm
• http//www.sciencejoywagon.com/explrsci/media/pris
  m.htm

44
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.

45
An incident light wave strikes a mirror at a 35o
angle with the surface of the mirror. What is
the angle of reflection?

• 35o
• 55o
• 65o
• 90o

46
___ refers to the bending of waves as the waves
pass through different mediums resulting in a
change in speed of the wave.

• diffraction
• reflection
• refraction
• interference

47
___ refers to waves that bend around the edge of
a barrier due to the dragging as the waves move
through the opening.

• diffraction
• reflection
• refraction
• interference

48
Rainbows are an example of the ___ of light.

• diffraction
• refraction
• reflection
• interference

49
An echo is an example of the ___ of sound.

• diffraction
• reflection
• refraction
• interference