Transcript Waves - Weebly

Waves
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.
The source of all wave motion is a
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movement of matter
harmonic object
vibration
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Waves are the transfer of
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energy
matter
vibrations
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
doesn’t make the wave; it merely carries
or transports the wave from its source to
another location.
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?
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The trumpet
The music he is producing
The air in the room
There is no medium
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Types of Waves
 Mechanical
waves
 Electromagnetic waves
 Matter wave
Mechanical waves
 Mechanical
waves require a material
medium
 Newton’s 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
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
Electromagnetic Spectrum
Which of the following electromagnetic
waves travel the fastest at room temp?
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Radio
Microwave
X-rays
None of the above
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Which of the following is NOT
an electromagnetic wave?
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Radio
Sound
Light
X-fays
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Matter waves
 Electrons
and other particles show wavelike behavior under certain conditions.
 Quantum mechanics is needed to describe
the properties of matter waves.
The type of wave that does not
require a medium is a(n)
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electromagnetic wave
mechanical wave
matter wave
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)
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electromagnetic wave
mechanical wave
matter wave
All waves travel at this speed
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This type of wave is governed by
Newton’s laws of motion.
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Electromagnetic wave
Mechanical wave
Matter wave
All types of waves
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The properties of this type of wave are
described by quantum mechanics.
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Electromagnetic waves
Mechanical waves
Matter waves
All types of waves.
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Sound is an example of this type of
wave.
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Electromagnetic
Mechanical
Matter
All of the above
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Light is an example of this type of
wave.
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Electromagnetic
Mechanical
Matter
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Types of Mechanical Waves
 Transverse
waves
 Longitudinal or compressional waves
 Surface waves
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
Transverse Waves
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
Longitudinal Waves
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
Surface Waves
A sound wave is an example of a
___ wave.
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longitudinal
transverse
standing
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.
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longitudinal
sound
transverse
compression
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Measuring a Wave

Wavelength (λ)- 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.
Measuring a Wave
Relationships between wave
properties
 Wavelength
and frequency are inversely
related. As wavelength increases,
frequency decreases.
 Frequency and period are inversely
related. (f=1/T or T=1/f)
 The velocity of a wave is equal to the
distance it can travel in a given time
period. v=d/t or v=λ/T or v=λf
The time needed for a wave to
make one complete cycle is its
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The amplitude of a wave is 1 meter.
The top-to –bottom distance of the
disturbance is
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If you double the frequency of a
vibrating object, its period
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halves
is quartered
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During a single period, the distance
traveled by a wave is
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one-half wavelength
one wavelength
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 wave’s 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.
Waves at Boundaries
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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/ewave6.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
When a wave encounters a boundary, the
wave that strikes the boundary is called the
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incident wave
reflected wave
refracted wave
normal wave
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When a wave encounters a boundary,
the wave that returns is called the
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reflected wave
refracted wave
normal wave
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When a wave is sent down a spring connected to a
wall, ___of the energy in the wave is reflected
back.
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A pulse is sent along a spring that is
attached to the wall. The reflected pulse is
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inverted with equal amplitude
inverted with a smaller amplitude
upright with equal amplitude
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.
Interference
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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 doesn’t 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
Interference (continued)
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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/interfer.htm
___ occurs when two or more waves move
through a medium at the same time.
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Refraction
Reflection
Interference
Resonance
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In destructive interference, a point that
experiences no displacement is called a
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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
Waves in Two Dimensions
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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.
Ray Diagram of Wave
Angle of reflection
Normal
Angle of incidence
Angle of incidence
Normal
Angle of reflection
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.
Refraction

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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)
Refraction
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.
Diffraction
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.
An incident light wave strikes a mirror at a 35o
angle with the surface of the mirror. What is the
angle of reflection?
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35o
55o
65o
90o
___ refers to the bending of waves as the
waves pass through different mediums
resulting in a change in speed of the wave.
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___ refers to waves that bend around the edge of
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through the opening.
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Rainbows are an example of the
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An echo is an example of the ___
of sound.
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