chapter 11: waves
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Chapter 11: WAVES. Section 1-The Nature of Waves. Examples of waves…. A surfer waits for the perfect wave Microwaves warm up leftover pizza A CD player brings music (sound waves) to your ears More examples of waves… - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 11: WAVES
Section 1-The Nature of Waves
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Examples of waves…
A surfer waits for the perfect waveMicrowaves warm up leftover pizzaA CD player brings music (sound
waves) to your earsMore examples of waves…Earthquakes--Energy is transferred in
powerful waves that travel through Earth. (Seismic waves)
Light--A type of wave that can travel through empty space to transfer energy from the Sun to the Earth.
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Drop a rock into a pool of water The rock has ENERGY
ENERGY is transferred to nearby water molecules
These molecules transfer ENERGY to other molecules
A wave is a repeating disturbance or movement that transfers ENERGY through matter or space.
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MECHANICAL WAVES Waves that can travel only
through matter are called
mechanical waves. (Ex. Sound waves require air.)
The matter the waves travel through is called the medium.
The medium can be a solid, a liquid, a gas or a combination of these.
Examples of mediums…
Sound waves = AIR
Ocean waves = WATER
Not all waves need a medium. Light and radio waves travel through space.
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There are 2 types of mechanical waves:1—TRANSVERSE Matter in the medium moves
back and forth at right angles to the direction that the wave travels.
Examples—ocean wave, rope
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2—COMPRESSIONAL
Matter in the medium moves back and forth in the same direction that the wave travels.
Examples—slinky, sound waves
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SEISMIC WAVESDuring an earthquake,
Earth’s crust vibrates, creating seismic waves that carry ENERGY outward.
These waves are a combination of TRANSVERSE and COMPRESSIONAL waves.
Compressional—P-waveTransverse—S-wave
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Chapter 11: WAVES
Section 2-Wave Properties
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What makes waves different from each other? The medium they travel in
How much energy they carry
How fast they travel
What they look like
What do they look like?
TRANSVERSE WAVES—
Have alternating high points (crests) and low points (troughs).
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Compressional waves do not have crests or troughs.
Compressional waves are made of 2 regions:
1. COMPRESSION-coils are close together (dense)
2.RAREFACTION-coils are far apart (less dense)
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A wavelength is the distance between a point on a wave and the nearest point just like it.
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FREQUENCY
The frequency of a wave is the number of wavelengths that pass a fixed point each second.
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Frequency = f
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THE ELECTROMAGNETIC SPECTRUM
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Frequency Frequency is expressed in
hertz (Hz).
A frequency of 1 Hz means that 1 wavelength passes by in 1 second.
In SI units, 1 Hz is the same as 1λ/s.
This relationship is always true—
as frequency increases, wavelength decreases.
f↑ = λ↓
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WAVE SPEED
SPEED = WAVELENGTH X FREQUENCY
v = λ x f (λ=2m, f=3Hz)v = 2m x 3Hz (3λ/s)v = 6m/s
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Wave Speed SPEED = WAVELENGTH X FREQUENCY
v = λ x f
Example: (do on your own)λ = 3 m, f = 10 Hz
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Why do some earthquakes cause terrible damage, while others are hardly felt?
Because the amount of energy a wave carries can vary.
AMPLITUDE is related to the ENERGY carried by a wave.
↑ wave’s AMPLITUDE = ↑ wave’s ENERGY
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If you’ve ever been knocked over by an ocean wave, you know that the higher the wave, the more energy it carries.
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CHAPTER 11: WAVES
Section 3-The Behavior of Waves
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REFLECTION-LIGHT WAVESTHE LAW OF REFLECTION—
REGULAR/SMOOTH SURFACESDIFFUSE REFLECTION—ROUGH
SURFACES
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REFLECTION—REGULAR OR DIFFUSE?
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REFLECTION—ALBEDO VALUES
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REFLECTION—SOUND WAVES
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REFLECTION—Echolocation—(bats and dolphins)Bat emits sound waves as they
fly.When the sound waves strike an object, the
waves are reflected back the to the bat.
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REFLECTION If you are one of the last people to leave
the school building…when you close your locker door, the sound echoes down the empty hall. ECHOES are caused by wave reflection.
REFLECTION occurs when a wave strikes an object and bounces off of it. (Examples--sound, light, water)
ECHO (REFLECTION OF SOUND WAVES)--Sometimes when the sound waves hit another object, they reflect off of it and come back to you. Your ears hear the sound again, a few seconds after you first heard your locker door slam.
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SONAR—uses sound waves to find objects that are underwater.
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ULTRASOUND—ultrasonic waves are directed into a pregnant women’s uterus to form images of her fetus.
Ultrasonic waves are directed into a pregnant woman’s uterus.
These sound waves form images of her fetus.
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CAFETERIA AND STAGE
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GYM AND CHORUS ROOM
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REFRACTION Remember that a wave’s speed
depends on the medium it is moving through.
When a wave passes from 1 medium to another—such as when a light wave passes from air to water—it changes speed.
REFRACTION is the bending of a wave caused by a change in its speed as it moves through 1 medium to another. (Example—RAINBOWS—LIGHT WAVES PASS FROM AIR TO WATER)
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REFRACTION
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REFRACTIONTo the observer on the side of the pool, the
swimmer’s feet look closer to the surface than it actually is.
The pencil looks like it is broken at the surface of the water.
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DIFFRACTION DIFFRACTION occurs when an object causes a
wave to change direction and bend around it. DIFFRACTION and REFRACTION both cause
waves to bend. The difference is that refraction occurs
when waves pass through an object, while diffraction occurs when waves pass around an object.
ALSO--refraction changes mediums
diffraction stays in the same medium
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DIFFRACTION
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INTERFERENCE
When 2 or more waves OVERLAP and combine to form a new wave, the process is called INTERFERENCE.
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INTERFERENCECONSTRUCTIVE--ADD DESTRUCTIVE--
SUBTRACT
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INTERFERENCE