WAVES
Unit 4
Mr. Olsen
What is a wave?
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A vibration or disturbance.
SOUND & LIGHT are forms of energy
that travel in waves.
Period (T)
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A period is the time it takes for one
cycle.
1 cycle = 1 complete trip
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1 trip back & forth
Around and back to the same point
1 wave = 1 cycle
Frequency (ƒ)
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# of cycles in one second.
# of waves in one second.
Measured in Hertz (Hz).
1 Hz = 1 cycle per second
Give it a try…
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A wave vibrates 100 times in 2 seconds.
What is its frequency?
100 waves in 2 seconds
100 waves per 2 seconds
50 waves/ 1 second
50 waves/ second = 50 Hz
Parts of a wave
Parts of a wave
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Crest= High point of a wave.
Trough=Low point of a wave.
Amplitude (A)= Distance from the
midpoint to the crest.
Wavelength (λ)= The length of one
complete wave.
Wavelength (λ)
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The length of one wave is measured
from a point on one wave to that same
point on the next wave.
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Crest to crest
Trough to trough
Midpoint (past crest & trough) to midpoint
Speed of a wave
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The speed of a wave depends on the
medium it travels through.
Medium is the material it passes
through.
Wave speed
(m/s)
= wavelength •
=
(m)
•
ν =•ƒ
frequency
(Hz)
What is the velocity of a wave that is 2 m
long with a frequency of 10Hz?
λ = 2m
ƒ = 10Hz
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=•ƒ
= (2m)(10Hz)
= 20m/s
Types of waves
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Teacher Tube Wave Video
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Transverse:
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The medium moves at a right angle to the direction of
the wave.
Examples: Light, Radio waves, Heat waves
Types of Waves
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Compressional
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A Compressional
wave is when matter
vibrates in the same
direction as the wave
travels.
These are also
known as
Longitudinal
waves.
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Longitudinal:
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The medium moves in the same direction as
the wave.
Example: Sound waves
Parts of a Compressional
Wave
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Compression: where the wave
“squeezes” or compresses the medium
Rarefraction: Where there is space in
the wave with no compression.
Type of medium
The type of medium changes the way a
wave moves.
Mediums with close molecules travel
quickly.
This is why waves travel better in liquids
and solids than in gases.
Waves through air
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However, air can still let waves pass at a
great speed.
The speed of sound through air is 344 m/s!
That is really fast!
What happens to a wave
when it runs into something?
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REFLECT- Bounce off
REFRACT- Break
DIFFRACT- Bend
GET ABSORBED- Soak into
PENETRATE- Pass through
Wave Rap
SOUND NOTES
(Click title to view video)
How does sound travel?
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Sound is a form of energy that moves in
waves through matter.
Sound waves are longitudinal waves
or compressional waves.
Properties of Sound Waves
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Sound waves move out from a
vibrating object in all directions.
As a sound wave travels further from the
object, the wave gets weaker.
How is sound produced?
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The movement of particles around a
vibrating object creates a sound
wave.
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Your vocal cords vibrate air molecules.
They vibrate other air molecules and so
on until the air molecules by the listener’s
ear vibrate their ear drum.
Speed of sound
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The speed of sound in air at room
temperature is about 344 m/s.
vSound in Air = 344 m/s
Speed of Sound
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If the particles are closer together, they
hit faster and the wave (sound) moves
faster.
Does sound move faster in:
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air or water?
water or steel?
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When one particle bumps another that
bumps another and so on, a sound is made.
IS THERE SOUND IN SPACE?
LOUD and soft Sounds
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Intensity: strength of a sound
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Which sound is more intense, an airplane or talking?
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Which has more energy?
Intensity is measured in Decibels.
Your ear hears intensity as volume of a sound.
Intensity of a wave
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The intensity of a wave is shown by the
amplitude.
An intense sound is LOUD so it has a
high amplitude.
LOUD
SOFT
Blue Man Group - Drum Painting
and
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The pitch describes
high and low
sounds.
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A high sound like a
flute has a high
pitch.
A low sound like a
tuba has a low pitch.
sounds
Pitch of a wave
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The pitch of a wave is shown by the
frequency.
A high pitch sound has a high frequency
and a short wavelength.
ECHOS
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When sound waves reflect, they make an
echo.
Sonar uses echo to locate objects under
water.
Ultrasound uses echos to “see” inside the
human body.
Teacher Tube Video –The Doppler Effect
LIGHT
Types of Light Waves
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Light waves are grouped by different
frequencies and wavelengths.
These are the different types of
electromagnetic waves.
Electromagnetic Spectrum
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Energy that is given off by electrons
that moves in waves.
Look at your pictures and answer
the questions:
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Which ELECTROMAGNETIC WAVE has the
most energy? The least?
Which ELECTROMAGNETIC WAVE has the
longest wavelength? The shortest?
As frequency increases, what happens to
energy?
As frequency increases, what happens to
wavelength?
As the wavelength increases, what happens
to the frequency of the waves?
Teacher Tube Video – The Electromagnetic Spectrum
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Radio waves
Microwaves
Infrared Waves
Visible Light Waves
Ultraviolet Waves
X-Ray Waves
Gamma Waves
Radio Waves
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Radio waves are
used for radio
broadcasts, amateur
radio, television, and
mobile phones.
Microwaves
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Microwaves can be
used to study the
Universe,
communicate with
satellites in Earth
orbit, and cook
popcorn.
Infrared Waves
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Infrared waves are
used to heat food at
restaurants, by
police scanners, in
your remote control.
Ultraviolet Waves
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UV Waves are used
in tanning and in
sterilization of
equipment.
X-Ray Waves
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X-Rays are so
strong, they can go
right through you!
Gamma Waves
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Gamma rays and XRays can cause cancer,
but gamma rays can
also be used to destroy
cancer cells: this is
called radio-therapy or
radiation.
LIGHT WAVES- Visible Light
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VISIBLE LIGHT is a
form of
electromagnetic
energy that we can
see.
Visible Light
White Light
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Sunlight is white light.
White light = every color of
light
PRISM
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A prism REFRACTS
white light into all its
colors!
What color light is refracted the most?
Visible Spectrum
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Visible Spectrum = the colors that you
can see.
All the colors of the rainbow
Visible Spectrum
Red (longest wavelength)
Orange
Yellow
Green
Blue
Indigo
Violet (shortest wavelength)
How does light travel?
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Light is made up of bunches of energy
called photons.
Light travels in waves.
Light is an example of a transverse
wave.
Speed of light
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Light travels fastest through empty spaces.
Light waves slow down or get stopped by
matter.
In air at room temperature, speed travels at:
v = 300 000 km/s = 3 X 108m/s
Remember, sound travels at 344 m/s, so light
is about 1,000,000 times faster!
Light & Optics
How do I see Light?
Materials that light hits can be:
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Opaque- (Solid)
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Transparent- (See-through)
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Does not let light pass through.
A door is opaque.
Lets light pass through.
A window is transparent.
Translucent- (Not clear)
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Lets some light pass through.
A glass of lemonade is translucent.
When light hits a material, the
light may:
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Reflect: Bounce off
Refract: Bend
Get Absorbed
Reflection
Law of Reflection
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The angle the light ray hits the mirror
equals the angle it bounces off.
The angle of incidence equals the angle
of reflection.
The Law of Reflection
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Diffusion = the breaking up of light
Think about roads…
Look at the curved mirrors.
What do you observe about the
reflection?
Sound waves that hit this would all
go to the microphone.
What color light is in the
middle?
Refraction
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Waves bend when
they pass into a
different medium.
This happens
because the speed
of light changes.
Refraction explains how lenses work:
Your eyes have color sensors.
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Thousands of rods & cones in your
eye tell your brain how much red, green
and blue light hits your eye.
How do we see colors?
When ALL of the colors of light
combine…
White light is produced.
The Sun gives off "white" light, a mixture of all the colors in the spectrum.
The object looks WHITE because an equal mixture of RED, BLUE, and GREEN
light is reflected off the object and interpreted by our eyes and brain as WHITE.
You can use a FILTER to
absorb a color of light.
Your TV works using little
pixels that look like this:
Any color can be made from a
combination of these three colors of
light.
When colors of pigment, (or paint)
combine:
Colors effect our mood!
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Red = Stimulating
Yellow = Excitement
Blue = Calming
Which would you eat?
Colorblindness
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Some people have trouble telling the
difference between colors.
Their rods and cones do not detect
differences.
The last test is the easiest to use.
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A person with normal color vision
will see a “5” in the dot pattern.
A person with Red/Green color
blindness (the most common) will
see a “2” revealed in the dots.
Sometimes your eyes get
tired!
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Your rods & cones get used to what
they see and it takes them some time
to go back to normal.
Sometimes, your eyes play
tricks on you!
Which guy is the tallest?
How many shelves are here?
Are these bricks in straight
rows?
Look at the center and move
closer to the screen!
Are the long lines parallel?
Look at the center & move your head.
Are the purple lines parallel?
Curved or straight?