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CH 10, 11 & 12
Waves
The Nature of
Waves
• Rhythmic disturbances that carry E
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through matter or space
Water waves transfer E through
water
Earthquakes transfer E with shock
waves through the Earth
Water and the Earth are the
MEDIUM—material through which
the waves transfers E
Medium can be liquid, solid, gas or
combination of these
Some waves do not need a
medium; radio and light waves can
travel through the emptiness of
space
Types of waves
• Transverse waves—the medium moves at right angles to the
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direction the wave travels
In a water wave the water moves up and down, while the wave
moves horizontally
Compression waves—the matter vibrates in the same direction
as the wave travels
Sound waves are compression waves—they need a medium to
travel---that is why you cannot hear sound in space
Transverse waves
• Crest are the highest points
• Troughs are the lowest
• Wavelength (λ) is the
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distance between 2 identical
points on adjacent waves—
doesn’t have to be crest to
crest or trough to trough
Amplitude is the distance
from the rest position of the
medium to the crest or
trough
Larger amplitude—larger
amount of E
Tsunamis carry ENORMOUS
amounts of E
• Frequency (f) is the number of crests that pass a certain place
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each second
Measured in Hertz (Hz) waves per second
As frequency goes up the wavelength becomes shorter (closer
together)
Wave velocity= λ x f
m/s = m x Hz
A wave in a wave pool has a frequency of .60 Hz and a
wavelength of 3.2 m. Calculate its velocity.
Whiteboards!
• You have a long rope and you are making waves
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by shaking it up and down. What is the wave’s
velocity if the wavelength is 1.2 m and the
frequency is 4.5 Hz?
A tsunami wave is 13.0 m in length, and has a
frequency of 200.0 Hz. Calculate the speed of
the wave.
Another wave is traveling at 25.6 m/s with a
wavelength of .2 m. Calculate its frequency.
Yet another wave is traveling at 122.0 m/s with
a frequency of 56.0 Hz. What is the wave’s
wavelenth?
Compression waves
• The area that is close together is the compression
• Less dense area is the rarefaction
• The matter does not move with the wave—only the E
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moves forward
EX Every time you hear a sound, you don’t feel a puff of
air along with it
Wavelength (λ) = 1 compression and 1 rarefaction
Frequency is the # of compressions that pass a place
each second
Amplitude is the amount of the compress—depends on
the E of the wave—more E, tighter compression
Sound waves
• When you speak your vocal cords
produce compression waves that
travel through the air causing
compressions and rarefactions
among the particles in the air
• Speed of sound waves depends on
the medium and its Temp
• Air is the most common, but liquids
and solids are better—WHY?
• Sound travels faster at warmer
Temps—WHY? 20°C: 344m/s and at
0°C: 332m/s
Humid better than dry conditions—
WHY?
Seismic
Waves
• Carry E outward like a pebble hitting the
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water—move out from the focus in all
directions
Epicenter is point on the Earth’s surface
directly above the focus
They can travel through the Earth and
on the surface
Seismic waves from the same
earthquake are recorded all over the
world using a seismograph
Richter scale is a numerical description
of the size of a seismic wave; an
increase of 1 on the scale represents a
10x increase in the size of the waves
EX a tremor of 2 on the scale has 10x
larger waves than a 1; a 3 has 100x
bigger waves than a 1
Earthquakes
• Primary waves (p)–
produce 3 types of
cause matter to stretch
and compress –they are
waves:
the fastest
• Secondary waves (s)—
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slower and they move
matter from side to side
like horizontal transverse
waves
Surface waves—seismic
waves that cause a
rolling motion in the rock
and soil, like vertical
transverse waves
Faults
• Strength of an
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earthquake depends
on how much E has
built up along the fault
3 types: Normal:
rocks above fault line
move down
Reverse: rocks move
up and over the rocks
on the other side—mts
are formed this way
Strike-slip: rocks on
both sides of the fault
slide past each other—
San Andreas fault is
this type—parts of CA
are moving north to
Alaska!
Electromagnetic Spectrum
• Transverse waves
EM waves
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produced by the motion
of electrically charged
particles
They do not require a
medium to transfer E
They travel through
empty space (vacuum)
at 300,000 km/s or
300,000,000m/s!
• Travel slower through
any type of matter but
still much faster than
sound waves
• All EM waves travel at
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the same speed in each
medium, but their
frequencies and λ differ
The shorter the λ, the
higher the frequency
Classified from low freq
(long λ) radio waves to
high freq (short λ)
gamma rays
Draw the EM spectrum in
your notes from pg 360
if you don’t have these
notes
Particle Theory (1905)
• Radiation not only carries
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E but also has
momentum which is
particle-like behavior
Einstein said that light is
composed of tiny massless bundles of radiation
called photons
Photons with high E can
damage matter, including
us!
• Radio waves: low freq,
Types of EM Waves
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very long λ, low photon E
Also used in TV, cell
phones, cordless phones:
sound is turned into
transverse waves (electric
currents) that represent
voice patterns and pitch
Microwaves have the
highest freq of all radio
waves
Used in communications
and cooking
They pass right through
paper, plastic and glass
w/o heating them (food
heats up causing the
container to heat up)
EM waves cont.
• Infrared Radiation (IR) is
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heat; most from the sun,
but warm objects give off
more IR than cooler
objects
Dr’s can measure the
amount of IR given off as
a diagnostic tool: tumors
give off more heat than
surrounding tissue; called
thermograms
Also used in military for
night vision and heat
seeking missiles
Visible Radiation
• We know this part of the
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spectrum by the name :
LIGHT
R—red
O—orange
Y—yellow
G—green
B—blue
I—indigo
V—violet
ROYGBIV
Red has the longest λ, violet
the shortest
Light is used in photosynthesis
Ultraviolet Radiation
• Higher freq, shorter λ
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than visible light
Higher photon E with
more penetrating power
UV is necessary for
vitamin D production in
skin cells BUT prolonged
and frequent exposure
leads to skin cancer
Ozone (O3) layer
protects us, but
continued use of CFC’s is
destroying this layer (go
to pg 364 and draw the
diagram in your notes)
Deadliest Rays!
• X-Rays were discovered by
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German physicist Wilhem
Roentgen in 1895
He couldn’t explain the
mysterious rays so he called
them “x-rays”
They are absorbed by dense
material (bone) but pass through
skin and muscles
Gamma rays have the highest
freq and the shortest λ, making
them the most penetrating of all
EM waves—can penetrate
through several cm of lead!
Used to kill cancer cells/tumors