Download Waves

Watch Video
“What do these things have in common?”
Do “The Wave”
“Waves”
What are they?
Where do they come from?
How are the made?
Good/Bad
1
Introduction to
Waves
Read Pg 335 (pdf 46)
2
Wave: a disturbance that repeats itself regularly in space and
time and transmits progressively from one particle of matter
to the next, without transporting the matter.
Waves are caused by vibrations and carry energy from one
place to another and effect changes.
These changes can be extremely useful or can cause
tremendous damage.
3
On The Side
The wave is an essential unifying concept of modern physics.
Matter and energy both share wave properties
Take for example what is known as the electron wave partial
duality theorem. Which says that an electron can exist as a
wave or as a particle.
In quantum physics all matter theatrically can be expressed as
a wave. This is part of the premise of transportation. By
having the ability to change mass into its wave function and
then reassemble it in a new location.
4
Just a Few Examples of Waves
ocean waves
sound waves
light waves
earthquakes
TV and radio waves
microwave ovens
X-rays
fiber optics
lasers
5
Wavelength: the distance between two successive wave
crests, the symbol for wavelength is lambda. ( λ )
Crest : the high point of the wave.
Trough: the low point of the wave.
Amplitude: the distance from the midpoint or rest position
of the wave to either the crest or trough of the wave.
6
Spring Demo
7
Classification of Waves
All waves can be classified as being either a mechanical wave or
an electromagnetic wave.
Mechanical waves: This type of wave requires medium material.
Examples, water waves, sound waves, or waves on a rope.
Electromagnetic waves: This type of wave does not require
medium material. Examples, light waves, radio waves, X-rays.
8
Mechanical waves can be broken down further into two
subcategories of waves.
Transverse wave: Waves that cause particles over which they
pass to vibrate at right angles to the direction in which the
waves are moving.
Example: picture a boat bobbing up and down in the water
as a wave passes by.
Spring Demo
9
Longitudinal wave: Waves that cause particles over which
they pass to vibrate parallel to the direction in which the
waves are moving.
Example: sound wave, which we will examine with
greater detail later in this chapter.
Spring Demo
10
Transverse vs Longitudinal
Video clip
11
Waves
Mechanical
Transverse
Water
Longitudinal
Sound
Electromagnetic
Transverse
Light
12
Some Cool Sites
http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html
http://phet.colorado.edu/index.php
http://www.edumedia-sciences.com/en/a251-transverse-wave
13
Wave pulse: A single pulse caused by a single disturbance or
vibration. A constant vibration would then produce a series of
continuous pulses referred to as a wave.
See phet site
14
Period: The time for one complete cycle, or vibration. The
symbol for period is ( T ).
Frequency: The number of cycles or vibrations that occur in one
second. The units of frequency are Hertz. ( Hz ). 1 Hz is one
vibration in one second. The symbol for frequency is ( f ).
Period and frequency are related by the following equation.
1
T
f
15
Example: A sound wave has a frequency of 262 Hz. What
is the period of the wave?
3.82 x 10-3 sec
16
Example: A mass oscillates up and down on on a spring. If
the mass completes 37 cycles in a 60 second period. What is
both the frequency and period of the oscillating mass.
f = 0.62 Hz
and T = 1.62 sec
17
Do
#’s 1- 4, Pg 341 (pdf 48)
18
The Universal Wave Equation
The universal wave equation helps us to determine wave
speed, by starting with the general relationship between
velocity distance and time.
d
v
t
Now lets modify this for waves.
19
A waves will travel a certain amount of distance, let’s say
one wavelength, in a certain amount of time.
The amount of time for one full wavelength to go by is
what we define as the period of a wave.
Therefore the standard equation for velocity can be
rewritten and as follows.
d
v
t
v

T
20
Now using the relationship between period and frequency we get.
v

1
f
rearrange and simplify to get
v  f
this is known as the Universal wave equation and relates
velocity, wave length, and frequency of a wave.
21
Example: A sound wave with a frequency of 262 Hz has a
wavelength of 1.29 m. What is the speed of the sound wave?
vf
 1.29  262 
 338 m s
22
Example: A sound wave produced by a clock chime 515 m
away is heard 1.50 sec later.
a) What is the speed of sound in air?
d
v
t
515

1.5
 343 m s
23
b) If the sound wave has a frequency of 436 Hz. What
is its period?
1
T
f
1

436
 2.29ms
c) What is his wavelength?
vf
v

f
343

436
 0.787 m
Example: A hiker shouts towards a vertical cliff 695 m
away. The echoes heard 4.00 sec later.
a) What is the speed of sound in air?
d
v
t
695

2.00
 348 m s
26
b) The wave length of the sound is 0.750 m. What is the
frequency?
vf
f 
v

347.5
f 
.750
 463Hz
c) What is the period of the wave?
1
T
f
1

463
 2.16ms
Example: A radio wave, a form of an electromagnetic wave,
has a frequency of 99.5 MHz. What is its wavelength?
vf
v

f
8
3 x10 m s

6
99.5 x10 Hz
 3.02m
29
Example: A typical light wave has a wavelength of 580 nm.
a) What is the wavelength of the light in meters?
a) 5.8 x 10-7 m
b) What is the frequency of the wave?
vf
f 
v

3 x108 m s
f 
5.8 x107 m
 5.2 x1014 Hz
30
Example: Water waves with wavelength 2.8 m, produced in
a wave tank, travel at the speed of 3.80 m/s. What is the
frequency of the vibrator that produced them?
vf
f 
v

3.80 m s
f 
2.8m
 1.4 Hz
31
Do
# 5 – 9, Pg 349 – 350 (pdf 49)
32
Reflections of Waves
The characteristic of a wave striking a different medium
and being bounced back, either totally or partially, is
termed reflection.
33
There are two different ways in which a wave pulse can
be reflected.
The first is when the medium has a fixed end, or in
other words the end in not allowed to move.
In this case the reflected
wave pulse is inverted.
34
The second way in which a wave can be reflected is when
the end of the medium is open or the end is allowed to
move.
In this case the reflected wave pulse is up right.
35
See phet site
If the wave strikes the medium at an angle then we have a
different story.
The wave will be reflected at an angle, this is know as the
law of reflection.
36
Do
#’s 1-7, Pg 353 (pdf 49)
37
Law of Reflection:
The angle of incidence to the normal is equal to the angle of
reflection to the normal. The normal being a ray
perpendicular to the surface.
38
39
Diffuse Reflection:
This type of reflection is characteristic of a wave striking a
rough surface and being reflected randomly (in all
directions).
For example, paper reflects light in all directions, therefore
you can read from any angle.
40
Sound Reflection:
The reflection of sound is sometimes referred to as an echo.
The percentage of sound reflected from a surface depends
on the nature of the surface.
For example you get a high reflection rate from a rigid,
smooth surface such as, Gym walls, and low reflection from
a soft, irregular surface such as, soft irregular walls in a
movie theater
41
The study of sound reflection is called acoustics.
42
Multiple sound reflections that cause sound to be
garbled are called reverberations.
43
Interference of Waves
When two or more waves occupy the same space at the
same time they are said to interfere with each other.
Since both waves are moving the interference will only
last for a short length of time. At which point the two
waves will continue on unchanged by the encounter.
For that period of time when the waves are interfering with
each other they can do so in two distinct ways known as
constructive interference and destructive interference.
44
Constructive interference results in a wave pulse that is
bigger than either individual pulse. ( ie: they add together)
45
46
Destructive interference results in a wave pulse that is smaller
than either individual pulse. ( ie: they subtract from each other)
47
See phet site
48
Superposition of Waves
The principle of superposition may be applied to waves
whenever two (or more) waves are travelling through the same
medium at the same time.
The waves pass through each other without being disturbed.
The net displacement of the medium at any point in space or
time, is simply the sum of the individual wave
displacements. This is true of both waves or pulses.
http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
49
Example: Use the principle of superposition to determine the
resultant wave.
50
Example: Use the principle of superposition to determine the
resultant wave.
51
Standing Waves
When many similar waves occupy the same medium there is a
continuous interference pattern.
Which consists of both constructive interference and
deconstruct interference.
Under ideal circumstances a standing wave can be established.
52
A standing wave is exactly as it’s name implies, a wave that
appears to be motionless and is simply standing in one place.
In actual fact there are many waves, all of which are moving,
but the overall pattern caused by the interference simply gives
the appearance of a stationary wave.
53
There are two main parts to the standing wave. The nodes,
this is the location of maximum destructive interference, and
the anti-nodes, this is the location of the maximum
constructive interference.
54
Video Clip
Ruben's Tube Experiment Physics Project
Tacoma Narrows Bridge Collapse
Do
#’s 1 – 5, Pg 362 (pdf 50)
56
Refraction
The velocity of a wave is dependent only on the medium in
which the way is traveling.
Therefore if you change the medium, the velocity of the wave
will also change.
This change in velocity then causes a change in the direction of
the wave.
57
This phenomenon is known as refraction.
58
http://www.physics.uoguelph.ca/applets/Intro_physics/re
fraction/LightRefract.html
http://physics.ham.muohio.edu/waveapplets/RefTest.html
Refraction can happen for either of the following circumstance
1) from a less dense to a more dense medium
When you run in to the water at the beach and you trip
and fall forward.
2) from a more dense to a less dense medium
light going from water to air causes a stick to
look bent or broken.
60
61
Refraction of light passing from air into glass
The ray of light entering the glass termed the incident ray.
The ray that travels in the glass is termed the refracted ray.
The angle between the incident ray and the normal is called
the angle of incidence.
The angle between the refracted ray and the normal is
called the angle of refraction.
62
63
The incident ray strikes the glass at an angle and the
refracted ray is bent “towards the normal”.
Since the light ray bends towards the normal as it passes
from air to glass (less dense to more dense), the angle of
incidence is greater than the angle of refraction.
When the light leaves the glass the ray is deflected “away
from the normal”. In this case the angle of refraction is
greater than the angle of incidence. (more dense to less
dense)
64
Air
θi
θr θ
i
Glass
θr
65
Laws of Refraction
From less dense to more dense medium the angle of
incidence is greater than the angle of refraction.
From more dense to less dense medium the angle of
refraction is greater than the angle of incidence.
66
A prism uses refraction to separate the various colors
of light composing the visible spectrum.
This occurs because all the colors that make up
white light do not travel at the same speed in glass
thus causing each color to bend different amounts.
67
This color separation is referred to as dispersion.
Rainbows work because the water drops act as tiny
prisms
68
Diffraction
You can usually hear a siren long before you see an
emergency vehicle, because sound can “bend” around
corners.
This characteristic of bending around a corner is not a
characteristic just for sound but for all waves in
general, and is known as the diffraction of waves.
69
Diffraction: The bending of waves around a barrier.
When a straight wavefront strikes a barrier the component of the
wave that is allowed to pass through the barrier will then
become bent and appear as a circular wave.
70
The amount of bending depends primarily on the width of the
opening maximum bending occurs when the width of the
opening is approximately one wave length.
http://www.ngsir.netfirms.com/englishhtm/Diffraction.htm
71
72
73
THE END
Please Read over Pg 371 in your text
Please do Pg 372&373
#’s
1, 2, 4, 5, 8, 9, 10, 11, 12, 14, 15,
16, 21, 22, 23, 24, 25, 27, 28.
74