Post on 02-Mar-2018
transcript
1
WAVES
How are waves generated?
Waves are generated by
2
Wave—a disturbance that transmits energy through empty space or through a medium
Medium—any solid, liquid, or gas
3
Types of Waves 1. Electromagnetic—consists of oscillating electric and
magnetic fields
a. Requires no medium
b. Ex: light, X-rays, radio, gamma rays
4
Types of Waves 2. Mechanical—energy transferred from one particle
of a medium to the next
a. Medium required
b. Ex: sound, water waves
c. 2 types: transverse & longitudinal
5
Wave Topics A. Period (p. 516)
B. Frequency (p. 516)
C. Wave Speed (p. 518-521)
D. Transverse Waves (p. 511)
E. Longitudinal Waves (p. 512)
F. The Parts of a Wave (p. 512, 514-515)
6
What type of mechanical wave
is this? TRANSVERSE
Transverse Wave Wave moves perpendicular to the particles of the
medium
8
TROUGH
CREST
WAVELENGTH
AMPLITUDE
Transverse Wave
What type of mechanical wave
is this?
Animation
http://www.kettering.edu/physics/drussell/Demos/waves/wavemotion.html
11
Longitudinal Wave Wave moves parallel to the particles of the medium
http://www.kettering.edu/physics/drussell/Demos/waves/wavemotion.html
12
Longitudinal Wave
COMPRESSION RAREFACTION
WAVELENGTH
Longitudinal Wave
Frequency
• # of waves/time
• Hertz (Hz)
Period
• time/wave
• Seconds (s)
1
f T
Wave Speed Depends on the medium
Wave speed = frequency x wavelength
v
f l
v: velocity (m/s)
f: frequency (Hz)
l: wavelength (m)
T: period
l
v T
18
What are two types of
mechanical waves?
Longitudinal
Transverse
Review What are the key parts of the following wave?
What are the appropriate units for frequency?
Frequency is the number of waves that pass a point each second. It is measured in Hertz (Hz).
19
Wave Sample Problems
Calculate the speed of waves in a puddle that are 0.650 m apart and made by tapping the water surface 5 times each second.
20
Wave Sample Problems Crickets produce a chirping sound based on the outside temperature. Some
chirps can have wavelengths in air of 1.25 m. If the speed of sound in air is 346 m/s, what is the frequency of the chirp produced by a cricket?
What is its wave period?
Wave Sample Problems A manatee can typically hear sounds with frequencies up to 32,000 Hz.
What is the speed of sound in water if a wave with this frequency has a wavelength of 10 cm. (Hint: Convert cm to meters.)
22
Wave Sample Problems
A buoy bobs up and down in the ocean. The waves have a wavelength of 6.3 m, and they pass the buoy at a speed of 12.8 m/s. What is the frequency of the waves?
How much time does it take for one wave to pass under the buoy ? (Hint: Find the wave period.)
Wave Practice Problems, Part 2 check your answers
3) 0.0076 m
4) 10 s
5) 0.0136 m
6) 38 m
7) 1.6 m/s
8) 129 Hz
0.0078 s
9) 15000 m/s
10) 1.6 Hz
0.625 s
Review
What are the key parts of the following wave?
What is the appropriate unit for wave period?
Wave period is the amount of time it takes for one wave to pass a given point. It is measured in seconds (s).
25
1. Quiz Review 2. Group Review
Game
A wave is disturbance that transmits ________
____________ waves consists of oscillating electric and magnetic fields and do not require a _________. Examples include ______________________.
___________ waves must have a medium because the energy is transferred from through the particles. There are two types of this wave __________ and ________.
26
ENERGY
ELECTROMAGNETIC
MEDIUM
ALL FORMS AND COLORS OF LIGHT
MECHANICAL
LONGITUDINAL
TRANSVERSE
TROUGH
CREST
WAVELENGTH
AMPLITUDE
The time it takes for one wave to pass a point is called _______________
The number of waves that pass in one second is called ______________
These variables are reciprocals (inverse) of each other. T= 1/F or F= 1/T
29
WAVE PERIOD (T)
FREQUENCY (F)
AFTER THE QUIZ WAVE BEHAVIORS GUIDED READING
Electromagnetic Spectrum
The Electromagnetic
Spectrum
• Vibrating magnetic & electric fields
• Can travel through a vacuum
• v = 3.00 x 108 m/s (in a vacuum)
Electromagnetic Waves
The Electromagnetic Spectrum
Radio Waves
• Lowest frequency
• Longest wavelength
• Radios, TVs, cell phones
Microwaves
• Used in cooking (microwave oven)
• Food absorbs wave
• Energy from wave converts to heat
Infrared
• “heat waves”
• Uses: keeping food
warm, animal tracking,
infrared photography
http://coolcosmos.ipac.caltech.edu/image_galleries/our_ir_world_gallery.html
Visible Light
• Different frequencies seen as different
colors
• ROYGBIV
• Red: lowest frequency, least energy
• Violet: highest frequency, most energy
Ultraviolet
• Higher frequency than light
• More penetrable
• Causes sunburns, damages tissue, kills
bacteria
X-Rays
• High energy
• Can penetrate soft tissue
• Uses: medical tests, checking luggage at
airport
Gamma Rays
• High frequency, short wavelength
• High energy
• Produced by nuclear particles
• Used in radiation treatment to kill cancer
cells
Draw a transverse wave and label the amplitude.
• Wave Behaviors Discussion
• Wave Behaviors lab
• Lab Explanations
Wave Behaviors
Reflection
Refraction
Diffraction
Interference
Wave Behaviors
Reflection
– Bounces off boundary
Refraction
– The bending of a wave as it moves from one medium to another
Diffraction
– The bending of a wave around a barrier
Reflection
Refraction
Diffraction
Interference
The combining of 2 waves
Two types:
– Constructive
– Destructive
Constructive Interference
Destructive Interference
Destructive Interference
Waves with different amplitudes
Standing Waves
Result from interference between a
wave and its reflected wave.
http://id.mind.net/~zona/mstm/physics/waves/standingWaves/understandingSWDi
a1/UnderstandingSWDia1.html
http://www.walter-fendt.de/ph14e/stwaverefl.htm
Node Antinode
refraction
Destructive interference
diffraction
reflection
Light & Wave Behaviors Lab
• When light passes
through a series of
tiny slits or grooves
called a diffraction
grating, light fans
out from each slit.
White light is
spread out into a
spectrum
according to
wavelength.
Refraction
• Pouring water in the
cup causes the light
to refract at a different
angle. This is why
the penny is no
longer in view when
looking at it from the
original viewing
angle.
• Light waves bounce
off the inner and outer
layers of the nail
polish film. At times
the waves interfere
constructively to
produce certain colors
and destructively to
produce other colors.
• You could see the
image of each other
when the angles
were the same. The
law of reflection
states that the angle
of incidence equals
the angle of
reflection.
How is amplitude altered during constructive/destructive interference?
• Constructive interference results a combined wave with a larger amplitude than the separate waves.
• Destructive interference results in a combined wave with a smaller amplitude than the separate waves.
• Wave Behaviors Discussion
• Wave Behaviors lab
• Lab Explanations
Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.
Constructive Interference
Amplitude = 7 cm
How are frequency and pitch of a sound wave altered as sound moves away from you?
• Sound Notes and Video Clips
• Resonance
• Speed of Sound & Sonic Boom
• Doppler Effect
Sound travels as a longitudinal wave
Sound waves are created by vibrations.
FREQUENCY
• Frequency is known as Pitch in sound waves
• Human hearing: 20 Hz to 20,000 Hz
• Infrasonic: <20 Hz
• Ultrasonic: >20,000 Hz
AMPLITUDE
• Amplitude is known as Loudness in
sound waves
• Loudness measured in decibels (dB)
Near total silence—0 dB
A whisper - 15 dB
Normal conversation - 60 dB
A lawnmower - 90 dB
A car horn - 110 dB
A rock concert or a jet engine - 120 dB
A gunshot or firecracker - 140 dB
More Sound Terminology…
• Natural Frequency is the frequency at
which an object naturally vibrates
• Resonance occurs when an outside
vibration matches the natural frequency
of an object causing it to vibrate
VELOCITY
• The speed of a sound wave depends on:
1. The type of Medium
• Fastest in solids
2. The Temperature of the medium
• Faster in warmer temps
Other Scenarios of Doppler
Effect • Object is traveling at the speed of sound
Other Scenarios of Doppler
Effect
• Object is traveling faster than the
speed of sound
• Creates sonic booms
Pitch and the Doppler Effect
Wavelength and Frequency Review
• As the wavelength increases, the
frequency ___________________.
• This means wavelength and frequency are
indirectly proportional.
• Which of these waves has the higher
frequency?
decreases
This one! It has the smaller wavelength.
Frequency and Sound
• Frequency = pitch
• Pitch—the highness or lowness of a sound
High frequency: high pitch Low frequency: low pitch
DOPPLER EFFECT
• The perceived change in frequency (pitch)
due to the motion of either the source of
the wave and/or the observer
How does it happen?
As a sound is created, the sound waves spread out in all directions around the source.
Then What?
If the source moves, the wave
becomes bunched up on one side and
more spread out on the other.
Doppler Effect
Lower pitch; longer wavelength
Lower frequency
Higher pitch; shorter wavelength
Higher frequency
If the sound is moving away from you . . .
If the sound is moving towards you . . .
So, what does that mean?
If the source is moving
towards you, the pitch sounds higher.
And if the source is
moving away from you, the pitch sounds
lower.
http://www.youtube.com/watch?v=-d9A2oq1N38
http://www.youtube.com/watch?v=gWGLAAYdbbc
http://www.youtube.com/watch?v=ofESdVdX-fY
http://www.youtube.com/watch?v=z0EaoilzgGE
http://youtu.be/h4OnBYrbCjY
http://youtu.be/sH7XSX10QkM
Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.
Constructive Interference
Amplitude = 7 cm
How are frequency and pitch of a sound wave altered as sound moves away from you?
Frequency will decrease as the sound moves away from you causing the pitch to seem lower.
• Sound Notes and Video Clips
• Resonance
• Speed of Sound & Sonic Boom
• Doppler Effect
REVIEW
Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm.
Destructive Interference
Amplitude = 3 cm
Echoes are examples of what wave behavior?
Reflections
80
1. Review of EM Spectrum 2. Wave Test Review
The Electromagnetic Spectrum
Question & Answer
Which EM wave has the longest wavelength, thus the lowest amount of energy?
Radio
Which EM wave is the only one that can be seen by the human eye?
Visible
Light
Which EM wave is shorter than radio waves, but longer than infrared?
Microwaves
Which EM wave aids in photosynthesis and provides vitamin D to people?
Ultraviolet
Which EM wave has the most energy and is the most intense and dangerous?
Gamma
Which EM wave is used at the airport to “see” through suitcases and bags?
X-rays
Which EM wave is the heat given off by objects?
Infrared
Conclusion
Electromagnetic Waves:
Can travel in a vacuum
Speed of all EM waves is
3.0 x 108 m/s in a vacuum
Slows down in gas, slower in liquids, slowest in solids
Review
BR: Classify this wave behavior.
Refraction
How is this different from Diffraction?
Refraction is the bending of a wave due as it enters a new medium, but diffraction is the bending of a wave around an obstacle or opening.
91
REVIEW Which wave behavior caused this glass to
break?
Resonance
What are the basic properties of sound?
96
1. Wave Stations 2. QR Code Questions
Sound Lab Summary
Pay close attention as we discuss some
of the things you say in the lab
activities. You will use this
information to explain how each
activity worked.
Sounds are produced by
vibrations.
Sound waves are LONGITUDINAL.
Frequency = Pitch
The shorter the wavelength, the
higher the pitch.
Humans can hear between 20
Hertz (infrasonic) and 20,000
Hertz (ultrasonic)
http://www.ultrasonic-ringtones.com/
Natural Frequency
All objects produce their
own unique frequency
and sound (timbre)
Resonance
When a sound matches
the natural frequency of
an object causing it to
vibrate
Amplitude = Loudness
Constructive interference
creates louder sounds
Media
Sound travels best (and
fastest) through solids
Sound cannot travel through
empty space
1. _______ creates louder sounds.
* constructive interference B. destructive interference C. diffraction
2. All objects produce their own unique
frequency and sound called ____.
A. resonance B. natural pitch * natural frequency
3. The longer the wavelength the
_____ the pitch?
A. longer B. higher * lower
4. When a sound matches the natural
frequency of an object causing it to
vibrate * resonance B. natural frequency C. tone
5. Sound travels best (and fastest)
through
A. gases * solids C. liquids
6. Sounds less than 20 Hz are
A. supersonic B. ultrasonic * infrasonic
REVIEW Which wave behavior caused this glass to break?
Resonance
What are the basic properties of sound?
Sound travels as a longitudinal wave and can experience many different wave behaviors: resonance, constructive/destructive interference, resonance, frequency/amplitude changes.
110
1. Wave Stations 2. QR Code Questions