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Transcript of s) Waves are oscillations and they transport energy. Medium: The matter through which a wave...
s)
Waves are oscillations and they transport energy.
Medium: The matter through which a wave travels
2 Subsets of Waves:
• Mechanical
waves that require a medium to travel through
(sound, water, earthquake• Electromagnetic waves that do not require amedium to travel
(light)
Most waves are caused by vibrating particles• Energy is transported, but the particle simply vibrate
in one small area
Waves are classified according to the direction inwhich the particleswave passes
in the medium move as the
2 Types:TransverseLongitudinal
Transverse WaveParticle motion is
perpendicular to thedirection of wave motion
Examples• water waves
• light waves• earthquake S-waves
Types of Waves
Wavelength =
length or size of one full oscillationAmplitude = from sitting wave to a crestCrest = highest point in the waveTrough = Lowest point in the waveResting State = The very middle, as if there were
no waves
Wave
motion
Longitudinal waveParticle ... _" moron ~
High dens
ity
LowdensityParticle motion is parallel
(a) P-wavto the directionmotion
of wave
Examples: compression rarefaction
I I~ J
• sound waves
• earthquake P-waves
I~~~I~~~I~Figure 1: Longitudittal '''ave
-.Compression
/t
•.•••.•• ....•
t·•·••·•·
••
• •••••• • • •• ••• • •• •••••• ••••
•• ••••••• •••••••
•••••••• ••••••••••
• •••••
•••
••
• •• ••'1••••
•••
••••••
• • •0.refactlo 0 /'
Compressions – Wave length
area where the mediumRarefaction –
is pushed close together
area where the mediumcompression
~,
is spread furtherrarefaction
J
apart
,-
, -,.r' r J ·l r
I
k..k.. ..
k.J.l.. ....to..
.... -l... ....k..
. ....k.J.-
F1igure 1: lon.~itudinal \"ave
Remember that thevibrating left and
moleculesright, NOT
are simplymoving from one
end to the other
http://www.ffn.ub.es/~albert/ones/wavemotion.html
λ= wavelength (meters (m))length or size of one oscillation
velocity (m/s)how fast the wave is traveling
frequency (Hertz (Hz))
of a wave
v =
f =How many full wavelengths per second occur
Measure from any identical two successive pointsSymbol for wavelength is lambda(λ)
and is measured in meters (m)
(m)5 10 15 20 25 30 35 40
Oscillation = 1 complete wave cycle There are 4 complete oscillation depicted
here
The distance from one crest to the next crest, orfrom one trough to the next trough.It can be between any two successive points actually!
Can exist in a longitudinal wave from onecompression to the next compression.We will only concentrate on TRANSVERSE waves.• --
•
::411
cR
Frequency = number of WAVES passing a stationarypoint per second
Symbol is f Measured in Hertz (Hz)
λ= v/f
λ = wavelength (meters (m))length or size of one oscillation
velocity (m/s)how fast the wave is traveling
frequency (Hertz (Hz))
of a wave
v =
f =How many full wavelengths per second occur
~~.
= v/f
The string of a piano that produces the note middle
C vibrates with a frequency of 262Hz. If the sound waves produced by this string have a wavelength in air of 1.3m, what is the speed of the sound waves?
λ= v/f1.3m = v /
262Hz340.6m/s =
v
Remember, a wave is just transporting energy! The 2 ways to increase the energy a wave carries.
• 1) Increase the amplitude of a
• 2) Increase the frequency of a
wave
wave(done by decreasing wavelength)
I
http://phet.colorado.edu/sims/wave-on-
a-string/wave-on-a-string_en.html .I.I I I 'II .1.
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http://www.youtube.com/watch?v=z0EaoilzgGE
Change in frequency of a wave due to relativemotion between source and observer.• A sound wave frequency change is noticed as a
change in pitch.
Basically, as an object making noise moves closerto you, the pitch of the noise will increase• Because the sound waves are compressed upon each other
As an object making noise moves away from you,the pitch of the noise will decrease• Because the sound waves are further away from each other
Sound normally occurs like this from a stationaryobject
B A
With a moving object, the sound being producedis not moving to each side evenly.
.
http://faraday.physics.utoronto.ca/PVB/Harrison/Flash/ClassMechanics/Doppler/DopplerEffect.html
http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm
Electromagnetic Spectrum
Wave - Review
Waves are oscillations that transport energy.
2 Types of waves: Mechanical – waves that require a medium to travel
through (sound, water, earthquakes)
Electromagnetic – waves that do not require a medium to
travel (light)
Nature of Electromagnetic Waves
Electromagnetic waves: are waves that travel without a medium.
(They can travel through empty space) They travel as vibrations in electrical and magnetic
fields.
Speed of electromagnetic waves = 300,000,000 m/s
OR 300,000km/s
Takes light 8 minutes to move from the sun to earth {93 million miles} at this speed.
Vocabulary Recap/Help Page
Wavelength – The distance from crest to
crest of a wave. How long the wave is in
meters.
Frequency – The number of waves that
pass a point in one second. Determines
the energy a wave has. Measured in
Hertz.
The Electromagnetic SpectrumElectromagnetic Spectrum—Consists of
waves at all possible energies, frequencies, and wavelengths. They are placed in order of increasing frequency
So what do we notice about the wave as we move further right on our diagram?
Radio Waves
Radio waves have the longest wavelengths and lowest
frequency in the electromagnetic spectrum. Wavelengths range from .1m to 100km
Used by Radios, TVs, RADAR systems, Cell Phones
Each radio station broadcasts in a different frequency Cellular phones use radio waves that are much smaller than TV
and FM radio waves.
Used by long range communications,
wireless networks, bluetooth, some
A microwave oven works by passing
and absorbed by the water/fat/sugar
in
against each other.together???
Microwaves
microwaves, cell phones, pagers,
radar detectors.
microwave radiation, through the food,
the food. The energy causes the food particles to vibrate
What’s the by product of things rubbing
THERMAL ENERGY!
cold objects
Infrared Light (below red)
IR light from the sun is what keeps
you warm Uses: remote controls, the
bottom of your mouse, night vision,
target acquisition and tracking by the military and short-ranged
wireless communication.
Thermography: test method that
records thermal patterns and temperatures across the surface
of an object. Warm objects give off more energy
than
eye.
yellow 570–590 nm
not present, but are a
Visible Light The ONLY portion of the violet 380–450 nm
EMS which can be blue 450–495 nm
detected by the human green 495–570 nm
Some colors like brown, orange 590–620
nm
pink, and magenta are red 620–750 nm
blend of different wavelengths. ―White light‖ can be broken down into each of the individual colors by using
a prism.
layer, more harmful types of UV light is blocked.
and burn.
Ultraviolet
(beyond violet) UV Light carries more energy than visible
light Because of absorption in the atmosphere’s ozone
This type of wave is what causes your skin to tan
Used in tanning beds and black lights Too much can cause skin cancer. Some birds (birds of prey) and bees can see in the UV light spectrum Used to kill bacteria. (Sterilization of equipment) Causes your skin to produce vitamin D
(good for teeth and bones in moderation)
Use sun block to protect against (UV rays) UV rays are also what cause ―sun bleaching‖when certain materials are left outside
shorter than ultraviolet.
imaging.
the less dense
tissues but
cause cancer
X-Rays
Waves longer than gamma,
Widely used in medical
Carry a great deal of energy
Has enough energy to
pass not bone. Teeth and Bones absorb x-rays
Too much exposure can
MOST ENERGY of entire EMSradiation emitted by a nuclear explosioncause serious damage when absorbed by living
Gamma Rays
Smallest Wavelength (Highest Frequency) =
Gamma rays are the most dangerous form of
Due to their high energy content, they are able to
cells. Naturally occur in:
Radioisotopes on Earth (Radium, carbon-14, uranium-235, etc)
Fission and fusion reactionsproduce
it Sun spots (most all of
radiation absorbed by atmosphere)
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What type of electromagnetic waves have the most energy?
What type has the longest wavelength?
What type has the highest frequency?
What visible light has the longest wavelength?
What visible light has the lowest frequency?
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Waves can interact with other waves, otherobjects, or change medium (travel throughdifferent substances) When a wave meets a new surface or boundery,
wave reflects
the
When athrough
When a
wave passes the edge of an object or passesan opening, the wave diffracts
wave passes from one medium to another atan angle, it will refract
Reflection is the bouncing back ofa wave when it hits a surface or boundary that is hard enough that it can’t travel through. Examples: water waves bouncing off
of a boat, images in a mirror (and glass or very still water), echos.
Light obeys the “Law of Reflection” The angle of incidence will equal the
angle of reflection
Flat Surfaces (like mirrors) Every single incident ray will
hit at the same angle, and bounce off at the same angle
Rough Surfaces (like wateror frosted glass) Every single incident ray will
hit at a different angle, and scatter when they reflect
Diffraction: When waves pass theedge of an object, or reach an
opening, they will bend or spread:
spread out as if they were created there ( for small openings)
bend around the object (when waves pass an edge)
Refraction: The bending of waves when they
pass from one medium to the next Occurs when waves reach a new medium (that ittravel through) at an angle.▪ Medium = the material the wave is traveling through
can
Each time a wave reaches a new medium, they aredeflected (change direction) as they change speed
The pencil looks broken because of refraction: The light traveling to/from the part of the pencil out of the water
does not everchange speeds. The light that travels to/from the part of the pencil in the waterhas to change speeds (and changes angles) as it enters the water. This causes light from each end to reach your eye at different angles.
Different substances have different angles ofrefraction
ie: Waves bend/change directions at different angles when
they enter that specific substance This is because waves travel at different speeds in
differentsubstances
The slower light travels through an object, the more light
will “bend” and change direction when it enters it
A laser and a glass cubeOnly wavelength, so it can’tseparate into different wavelengths- That single wavelength slows down in
the glass cube to the left
White Light and a PRISMWhite light is made of ROYGBIV, many
different wavelengths. It canseparate into different wavelengths
- Each wavelength slows down at a different rate, separating in the prism to the right
Light slows down when it enters a prism and “bendsdown” when it strikes at this angle. Each wavelength of light slows down and bends differently. Violet end slows down more than the red end, so it bends
more. When light exits the prism, it speeds back up and
bends down again.
Water will do the same thing… it will refract light.
When light enters water, it will slow down (or bend) This causes objects underwater to appear as if they are
somewhere else. The light is tricking your eye.
Water will do the same thing… it will refract light.
Sometimes waves will interact with other waves…
Interference: When several waves are in the same
location, they combine to produce a single, new
wave that is different than the original wave
Once the waves pass through each other, they willtheir original shape and continue on their path.
return to
2
types
Constructive (add to each other)
Destructive (cancel each other out)
When the CREST of one wave overlaps the CREST of
another wave the waves reinforce each other
These wave are also called “in phase” When this happens, the amplitude INCREASES
http://www.acs.psu.edu/drussell/demos/superposition/sup
erposition.html
When the CREST of one wave overlaps the TROUGH of
another wave, the resulting wave has a SMALLERamplitude than the larger of the two original waves
When this happens, the waves can even cancel out These wave are also called “out of phase”
http://www.kettering.edu/physics/drussell/Demos/superposition/superposition.html
A lens is an optical device with symmetry
transmits AND refracts light We have 2 types of lenses:
that
Convex (converging) and
concave
(diverging)
We can either use:
A Simple Lens: one lens
▪ Examples: reading glasses,
magnifying glass, your retina
A Compound Lens: uses more than one lens
▪ Examples: telescope, microscope, cameras, etc
Lenses caneither be: Convex
(converging)
OR
Concave (diverging)
An eye that can see at20/20 vision will allowlight to focus directlyat the back of theretina.If you don’t see 20/20,your focal point is notdirectly on the retina,and you get a blurryimage
To correct nearsighted eyes (myopia), you use concave lenses They move the focal
point backward To correct farsighted
eyes (hyperopia), glasses will be made with convex lenses They move the focal
point forward.