Upload
truongbao
View
215
Download
1
Embed Size (px)
Citation preview
BIG Idea
Science Journal
Sound and light are waves thatare described by their frequencyamplitude and wavelength
111 SoundSound waves are
compressional waves generatedby a vibrating object
112 Reflection andRefraction of Light
Light waves can beabsorbed transmitted or reflected when they interactwith matter
113 Mirrors Lenses andthe Eye
Images of objectsseen by the eye can be changedby mirrors and lenses
114 Light and ColorThe color of an
object depends on the wavelengths of light emitted orreflected by the object
Cracking the SoundBarrierHave you ever heard thecrack of a sonic boom Asonic boom occurs when aplane exceeds the speed ofsound Sound waves create a cone-shaped shock wavecoming from the aircraftBehind the cone are low-pressure regions that cancause water vapor to con-dense forming the cloud you see here
Write three things you wouldlike to learn about sound
MAIN Idea
MAIN Idea
MAIN Idea
MAIN Idea
318318AFPCORBIS
null
32914271
eng - iTunNORM 00000309 00000000 00001503 00000000 0000009C 00000000 00005E79 00000000 0000028D 00000000
null
18306836
eng - iTunNORM 00000209 00000000 0000546E 00000000 0002726D 00000000 00006090 00000000 000192F5 00000000
319319
Sound and Light Make the
following Foldable to help you
identify ways in which sound
and light are different and alike
Fold one sheet of paper lengthwise
Fold into thirds
Unfold and draw overlapping ovals
Cut the top sheet along the folds
Label the ovals as shown
Constructing a Venn Diagram As you read the
chapter list the characteristics unique to sound
under the left tab the characteristics unique to
light under the right tab and those common to
both under the middle tab
STEP 4
STEP 3
STEP 2
STEP 1
What sound does a ruler make
Musical instruments come in many shapes
and sizes Some have strings some have hol-
low tubes and others have keys or pedals
They are played with various techniques
These differences give each instrument a
unique sound What would an instrument
made from a ruler sound like
1 Complete the safety form
2 Firmly hold one end of a thin ruler lying
flat on a desk allowing the free end to
extend beyond the edge of the desk
3 Gently pull up on and release the end of
the ruler What do you see and hear
4 Vary the length of the overhanging por-
tion and repeat the experiment several
times
5 Think Critically In your Science Journal
write instructions for playing a song with
the ruler Explain how the length of the
overhanging part of the ruler affects the
sound
Start-Up Activities
Preview this chapterrsquos contentand activities at gpesciencecom
Sound LightBoth
AFPCORBIS
320 CHAPTER 11 Sound and Light
Sound WavesAn amusement park can be a noisy place With all the racket
of carousel music and booming loudspeakers it can be hard tohear what your friends say The many sounds you hear every dayare different but they do have something in commonmdasheachsound is produced by an object that vibrates
Making Sound Waves When an object like the tuning forkin Figure 1 vibrates it creates sound waves Sound waves arecompressional waves Recall that a compressional wave is made ofcompressions and rarefactions When an end of the tuning forkmoves outward it forms a compression on that side by pushingthe molecules in air together The compression moves away fromthe tuning fork as these molecules collide with other molecules inair When the end of the tuning fork moves back a rarefaction isformed where the molecules are farther apart As the tuning forkvibrates it produces a series of compressions and rarefactions thattravels outward This series of compressions and rarefactions isthe sound wave that you hear
The Speed of SoundA sound wave moves in air as collisions between the mole-
cules in air transfer energy from place to place Sound waves alsocan move in other materials The material in which a sound wavemoves is called a medium Just as in air sound waves travel insolids liquids and other gases as a vibrating object transfersenergy to the particles in the material However sound wavescannot travel in empty space where there are no particles
Sound
Figure 1 A vibrating tuning fork
produces compressions and rarefac-
tions that travel outward from the
tuning fork These compressions
and rarefactions form a sound
wave
Reading Guide
Explain how sound travels
through different mediums Explain different properties of
sound Discuss the Doppler effect Identify ways sound can be used
Sounds are one way that you learn
about the world around you
Review Vocabulary
vibration rhythmic back-and-forth
motion
New Vocabulary
bull intensity
bull loudness
bull decibel
bull pitch
bull Doppler effect
Compression
Rarefaction
null
10198071
eng - iTunNORM 000003B6 00000000 00002C63 00000000 000096B6 00000000 00005FD4 00000000 000083A1 00000000
SECTION 1 Sound 321
The Speed of Sound in Different Materials The speedof a sound wave in a medium depends on the type of substanceand whether it is a solid liquid or gas For example Table 1
shows the speed of sound in different mediums at room temper-ature In general sound travels slowest in gases and fastest insolids
Temperature and the Speed of Sound The speed ofsound waves also depends on the temperature of the mediumAs the temperature of a substance increases its atoms andmolecules move faster At a higher temperature atoms andmolecules collide with each other more frequently As a resultsound waves move faster For example in air at a temperature of0C sound travels at a speed of 331 ms but in air at a temper-ature of 20C sound travels at 343 ms
Amplitude and Energy of Sound WavesThink about the differences among sounds you hear Some
are loud others are soft The flute plays high notes whereas thetuba is much lower What properties of sound waves cause thesedifferences in the sounds you hear
Recall that the amount of energy a wave carries correspondsto its amplitude For a compressional wave amplitude is relatedto the density of the particles in the compressions and rarefac-tions A vibrating object makes a wave by transferring energy tothe medium More energy is transferred to the medium whenthe particles of the medium are forced closer together in thecompressions and spread farther apart in the rarefactions Lookat Figure 2 A sound wave has a higher amplitude and carriesmore energy when particles in the medium are closer togetherin the compressions and more spread out in the rarefactions
Compression Rarefaction
Low-amplitude sound wave
Compression Rarefaction
High-amplitude sound wave
Figure 2 The amplitude of a
sound wave depends on the density
of the particles in the compressions
and rarefactions
In a high-amplitude sound wave
particles are tightly packed in the
compressions and far apart in the
rarefactions
In a low-amplitude sound wave
particles are less tightly packed in
the compressions and not as far
apart in the rarefactions
Table 1 Speed of Soundin Different Mediums
Medium Speed of Sound (ms)
Air (20degC) 343
Cork 500
Water 1498
Brick 3650
Aluminum 5000
null
10762286
eng - iTunNORM 0000039B 00000000 000024E4 00000000 0000BED0 00000000 00006069 00000000 00005378 00000000
Intensity and LoudnessImagine you are listening to music from your CD player
Sound waves produced by the CD player travel through the airand transfer energy from the CD player to your ears The energythat reaches your ears depends not only on the amplitude of thesound waves but also on how close you are to the CD playerFigure 3 shows that as you get farther from a source of soundthe energy of the sound waves is spread over a greater area Theamount of energy transferred by a sound wave through a certainarea each second is the intensity of the sound wave As soundwaves travel away from the source of the sound the intensity ofthe waves decreases as the waves spread out This means that asyou get farther from the source less energy reaches your earseach second
Loudness When you hear different sounds you do not needspecial equipment to know which sounds have greater intensityYour ears and brain can tell the difference Loudness is thehuman perception of sound intensity As the intensity of asound wave increases the loudness of the sound also increases
How are intensity and loudness related
A Scale for Sound Intensity The intensity of sound can bedescribed using a measurement scale Each unit on the scale forsound intensity is called a decibel abbreviated dB On this scalethe faintest sound that most people can hear is 0 dB Soundswith intensity levels above 120 dB may cause pain and perma-nent hearing loss During some rock concerts sounds reach thisdamaging intensity level Wearing ear protection such asearplugs around loud sounds can help protect against hearingloss Figure 4 shows some sounds and their intensity levels indecibels
Figure 4 The decibel scale meas-
ures the intensity of sound
Identify where a normal speakingvoice would fall on the scale
Figure 3 The intensity of a
sound wave decreases as the wave
spreads out from the source of the
sound The energy of the wave is
spread over a larger area as the
wave spreads out
Whisper
Rustling
leaves
Noisy
restaurant
20 25 50 75 80 100 110 12015
Purring
cat
Average
home
Vacuum
cleaner
Jet plane
taking off
Power
mowerPain
threshold
0dB 150
Loudness in Decibels
322 CHAPTER 11 Sound and Light
null
11326502
eng - iTunNORM 0000036D 00000000 00002027 00000000 00005FB6 00000000 0000601D 00000000 0000E76D 00000000
SECTION 1 Sound 323
Pitch and FrequencyYou might be familiar with the music
scale do re mi fa sol la ti do shown inFigure 5 If you were to sing this scale youwould hear the pitch of your voice gethigher Pitch is the human perception ofthe frequency of sound waves Pitch getshigher as the frequency of the sound wavesincreases
Frequency Frequency is a measure of how many wavelengthspass a particular point each second For a compressional wavesuch as sound the frequency is the number of compressions orthe number of rarefactions that pass by each second Frequencyis measured in hertz (Hz) A frequency of 1 Hz means that onecomplete wavelength passes by in 1 s
A healthy human ear can hear sound waves with frequenciesfrom about 20 Hz to 20000 Hz The human ear is most sensi-tive to sounds in the range of 440 Hz to about 7000 Hz In thisrange most people can hear much fainter sounds than they canat higher or lower frequencies
Ultrasonic and Infrasonic Waves Most people canrsquot hearsound frequencies above 20000 Hz which are called ultrasonicwaves Dogs can hear sounds with frequencies up to about35000 Hz and bats can detect frequencies higher than 100000Hz Even though humans canrsquot hear ultrasonic waves they havea number of uses For example ultrasonic waves directed intothe human body are used in medical diagnosis and treatmentUltrasonic waves are reflected by objects underwater and can beused to determine the size shape and depth of underwaterobjects
Infrasonic or subsonic waves have frequencies below20 Hzmdashtoo low for most people to hear These waves are pro-duced by sources that vibrate slowly such as wind heavymachinery and earthquakes Although you canrsquot hear infrasonicwaves you might feel them as a rumble inside your body
The Doppler EffectImagine that you are standing at the side of a racetrack with
race cars zooming past As they move toward you the pitches oftheir engines become higher As they move away the pitchesbecome lower The change in pitch or frequency due to therelative motion of a wave source is called the Doppler effect
Figure 5 Every note has a
different frequency which gives it
a distinct pitch
Describe how pitch changes whenfrequency increases
C
do
262
Hz
D
re
294
Hz
E
mi
330
Hz
F
fa
349
Hz
G
sol
392
Hz
A
la
440
Hz
B
ti
494
Hz
C
do
523
Hz
Comparing IntensityProcedure 1 Complete the safety form
2 Tie the middle of a 50-cm
length of string to a metal
object such as a spoon3 Wrap each end of the
string around a finger on
each hand Place one of
these fingers in each ear
4 Swing the object so it
bumps against a table or
a chair Note the sound
5 Take your fingers out of
your ears and repeat
step 4
Analysis1 Compare the sounds you
heard in both trials
2 Compare the intensity of
the sound waves that
reached your
ears in both
trials
null
14220886
eng - iTunNORM 000002DB 00000000 0000267E 00000000 0002136D 00000000 00006020 00000000 0000B99C 00000000
324 CHAPTER 11 Sound and Light
A Moving Source of Sound As a race car moves it producessound waves in the form of compressions and rarefactions InFigure 6A the race car creates a compression labeled ACompression A moves through the air toward the flagger By thetime compression B leaves the race car in Figure 6B the car hasmoved forward Because the car has moved since the time it createdcompression A compressions A and B are closer together in frontof the car than they would be if the car had stayed still Because thecompressions are closer together more compressions pass by theflagger each second than if the car had been at rest As a result theflagger hears a higher pitch Figure 6B also shows that the compres-sions behind the moving car are farther apart resulting in a lowerfrequency The flagger hears a lower pitch after the car passes
A Moving Listener You also can hear the Doppler effect whenyou are moving past a sound source that is standing still Supposeyou were riding in a school bus and passed a building with a ring-ing bell The pitch would become higher as you approached thebuilding and lower as you rode away from it The Doppler effecthappens any time the source of a sound is changing position rel-ative to the listener It occurs no matter whether it is the soundsource or the listener that is moving The faster the change inposition the greater the change in frequency and pitch
How does pitch change if you are moving awayfrom a sound source
The race car creates compression A which
spreads through the air in all directions from the
point where it was created
The car is closer to the flagger when it creates
compression B Compressions A and B are closer
together in front of the car so the flagger hears a
higher-pitched sound
Figure 6 The Doppler effect occurs when the
source of a sound wave is moving relative to a
listener
Compression A
Compression B
Compression A
Red Shift The Dopplereffect can also beobserved in light wavesemanating from movingsourcesmdashalthough thesources must be movingat tremendous speedsAstronomers have learnedthat the universe isexpanding by observingthe Doppler effect in lightwaves Research thephenomenon known asred shift and explain inyour Science Journal howit relates to the Dopplereffect
null
9174124
eng - iTunNORM 0000031A 00000000 00001D68 00000000 00006814 00000000 000060FA 00000000 00007D4E 00000000
SECTION 1 Sound 325
Using SoundWhen sound waves strike an object they can be absorbed by
the object transmitted through the object or reflected from theobject By detecting the sound waves reflected from an objectthe size shape and location of an object can be determined
Echolocation and Sonar Some species of bats as well asdolphins whales and other animals use sound waves to detecttheir prey Echolocation is the process of locating objects byemitting sounds and detecting the sound waves that reflect back
Sonar is a system that uses the reflection of underwater soundwaves to detect objects First a sound pulse is emitted underwa-ter The sound waves travel in the water and are reflected whenthey strike an object such as a fish or a ship An underwatermicrophone detects the reflected waves Because the speed ofsound in water is known the distance to the object can be calcu-lated by measuring how much time passes between when thesound pulse is emitted and when the reflected signal is received
USING SONAR A sonar pulse returns in 300 s from a sunken ship that is directly below Find
the depth of the ship if the speed of the pulse is 1500 ms Hint The sonar pulse travels a
distance equal to twice the depth of the ship so use the equation d = st2 to find the depth
known values and the unknown value
Identify the known values
speed of sound in water s 1500 ms
time for round trip t 300 s
Identify the unknown value
depth of the ship d m
the problem
Substitute the known values s 1500 ms and t 300 s into the equation for depth
d s2t
(1500 m2s)(300 s)
12
(4500 m) 2250 m
your answer
Check your answer by dividing the distance by the time and multiplying by 2 The result
should be the speed of sound given in the problem
CHECK
SOLVE
means
means
means
IDENTIFY
Solve a Simple Equation
Find the speed of a sonar pulse that returns in 20 s from a ship at a depth of 1500 m
For more practice problems go to page 879 and visit Math Practice at gpesciencecom
Topic SonarVisit for Web
links to information about ways
sonar is used
Activity Research to find out
the different types of sonar Make
a poster that describes active and
passive sonar
gpesciencecom
null
65358925
eng - iTunNORM 00000306 00000000 0000171B 00000000 0000C4D6 00000000 0000611C 00000000 0000D29C 00000000
326 CHAPTER 11 Sound and Light
Self Check
1 Explain how sound travels from your vocal cords to
your friendrsquos ears when you talk
2 Explain how the loudness of a sound wave depends on
the intensity of the sound wave
3 Draw and label a diagram that explains the Doppler
effect
4 Describe at least three uses of ultrasonic technology in
medicine
5 Think Critically How could sonar technology be used
to locate deposits of oil and minerals
Summary
Sound Waves
bull Sound waves are compressional waves that
are produced by vibrating objects
bull Sound usually travels fastest in solids and
slowest in gases
bull Sound travels faster as the temperature of
the medium increases
Properties of Sound
bull The amplitude of sound waves increases as
the density of particles increases in the com-
pressions and decreases in rarefactions
bull Loudness is the human perception of the
intensity of sound waves Pitch is the human
perception of the frequency of sound waves
bull The Doppler effect is the change in the fre-
quency of a sound wave when the source of
the sound is moving relative to a listener
6 Calculate Time How long would it take a sound
wave from a car alarm to travel 10 km in air if the air
temperature were 0degC
7 Calculate Distance If sound travels in the ocean with
a speed of 1500 ms how far will a sonar pulse travel
in 45 s
Ultrasound in Medicine High-frequency soundwaves can also be used to remove dirt buildup on jew-elry and glassware One of the most important uses ofultrasonic waves though is in medicine Using spe-cial instruments medical professionals can sendultrasonic waves into a specific part of a patientrsquosbody Reflected ultrasonic waves are used to examinedifferent body parts and to detect and monitor cer-tain types of heart disease and cancer Ultrasoundimaging also is used to monitor the development of afetus as shown in Figure 7 However ultrasound doesnot produce good images of the bones and lungsbecause hard tissues and air absorb the ultrasonicwaves instead of reflecting them
High-frequency sound waves can be used to treatcertain medical problems For example sometimes small harddeposits of calcium compounds or other minerals form in thekidneys making kidney stones In the past physicians had toperform surgery to remove kidney stones Now ultrasonic treat-ments are commonly used to break them up instead Bursts ofultrasound create vibrations that cause the stones to break intosmall pieces that can easily pass out of the body with the urineA similar treatment is available for gallstones
Figure 7 Ultrasonic waves are
directed into a pregnant womanrsquos
uterus to form images of her fetus
More Section Review gpesciencecom
null
7679998
eng - iTunNORM 000002D2 00000000 00003376 00000000 00010897 00000000 000060E0 00000000 000100BC 00000000
Opaque
Translucent
Transparent
SECTION 2 Reflection and Refraction of Light 327
The Interaction of Light and MatterLook around your darkened room at night You know that
some of the objects are brightly colored but they look gray orblack in the dim light Turn on the light and you can see all theobjects in the room clearly including their colors What you seedepends on the amount of light in the room and the color of theobjects For you to see an object it must reflect or emit somelight that reaches your eyes
Absorption Transmission and Reflection Objects canabsorb light reflect light and transmit lightmdashallow light to passthrough them The type of matter in an object determines theamount of light it absorbs reflects and transmits For examplethe opaque material in the top candleholder in Figure 8 onlyabsorbs and reflects lightmdashno light passes through it As a resultyou cannot see the candle inside Materials that allow some lightto pass through them like the material of the middle candle-holder in Figure 8 are described as translucent You cannot seeclearly through translucent materials
Transparent materials such as the bottom candleholder inFigure 8 transmit almost all the light striking them so you cansee objects clearly through them Only a small amount of lightis absorbed and reflected by transparent materials
Reflection andRefraction of Light
Reading Guide
Describe how light waves interact
with matter Explain the difference between
regular and diffuse reflection Define the index of refraction of a
material Explain why a prism separates
white light into different colors
The images you see every day are
due to the behavior of light waves
Review Vocabulary
visible light an electromagnetic
wave with wavelengths between
about 400 and 700 billionths of a
meter
New Vocabulary
bull opaque
bull translucent
bull transparent
bull index of refraction
Figure 8 These candleholders
interact with light differently
null
83748184
eng - iTunNORM 00000323 00000000 00001D68 00000000 000014D0 00000000 0000602F 00000000 00005BA1 00000000
328 CHAPTER 11 Sound and Light
Reflection of LightHave you glanced in a mir-
ror today You see your reflec-tion in the mirror when light isreflected off you strikes themirror and is reflected off themirror into your eye Becauselight behaves as a wave itobeys the law of reflection asshown in Figure 9 Recall thataccording to the law of reflec-tion the angle at which a lightwave strikes a surface is thesame as the angle at which it is
reflected Light reflected from any surfacemdasha mirror or a sheetof papermdashobeys this law
Regular and Diffuse Reflection Why can you see yourreflection in a store window but not in a sheet of paper Theanswer has to do with the smoothness of the surfaces A smootheven surface such as a pane of glass produces a sharp image byreflecting parallel light waves in only one direction Reflection oflight waves from a smooth surface is regular reflection To causea regular reflection the roughness of a surface must be less thanthe wavelengths it reflects A sheet of paper has an uneven sur-face that causes incoming parallel light waves to be reflected inmany directions as shown in Figure 10 Reflection of light froma rough surface is diffuse reflection
Scattering Diffuse reflection is a type of scattering thatoccurs when light waves traveling in one direction are made totravel in many different directions Scattering also occurs whenlight waves traveling through the air reflect off small particlesAn example is light scattering off the small water droplets thatmake up a cloud Scattering causes the cloud to appear whiteeven though the droplets are transparent
What is scattering of light
Figure 9 According to the law of
reflection light is reflected so that
the angle of incidence always
equals the angle of reflection
Figure 10 A sheet of paper
has an uneven surface that
produces a diffuse reflection
Explain Use the law ofreflection to explain why arough surface causes parallellight waves to be reflected inmany directions
Mirror
i = angle of
incidence
i
r
i
r
r = angle of
reflection
Normal
Normal
null
10673475
eng - iTunNORM 0000035A 00000000 00002CF2 00000000 00001672 00000000 000060C2 00000000 0000DDF0 00000000
Refraction of LightWhat occurs when a light wave passes from one material to
anothermdashfrom air to water for example Recall that refractionis caused by a change in the speed of a wave when it passes fromone material to another If the light wave is traveling at an angleto the boundary between the materials and the speed of light isdifferent in the two materials the wave will be bent or refracted
Why does refraction occur
The Index of Refraction The amount of bending that takesplace depends on the speeds of light in both materials Thegreater the change in speed the more the light will be bent asit passes at an angle from one material to the other Figure 11
shows an example of refraction Every material has an index ofrefraction which is the ratio of the speed of light in a vacuum tothe speed of light in the material The index of refraction indi-cates how much the speed of light is reduced in the materialcompared to its speed in empty space
The larger the index of refraction the more light is sloweddown in the material For example because glass has a largerindex of refraction than air light moves more slowly in glassthan air The index of refraction is usually largest for solids andsmallest for gases
Prisms A sparkling glass prism hangs in a sunny windowrefracting the sunlight and projecting a colorful pattern onto thewalls of the room How does the refraction of light create thesecolors The spectrum of colors is produced because the speed oflight in a material also depends on the wave-length of the light In a glass prism light waveswith longer wavelengths such as red light wavesare slowed less than light waves with shorterwavelengths such as blue light waves
Figure 12 shows what occurs when whitelight passes through a prism White light suchas sunlight is made up of light waves withrange of wavelengths from red to blue The tri-angular prism refracts the light twicemdashoncewhen it enters the prism and again when itleaves the prism and reenters the air Becausethe longer wavelengths of light are slowed lessthan the shorter wavelengths are red light isbent the least As a result of these differentamounts of bending the different colors areseparated when they emerge from the prism
Figure 11 The spoon looks
broken because light waves are
refracted as they change speed
when they pass from the water to
the air
329
Figure 12 Refraction causes a
prism to separate a beam of white
light into different colors
null
14367186
eng - iTunNORM 0000039D 00000000 000035C6 00000000 0000C58D 00000000 000060DD 00000000 0001DFCB 00000000
330 CHAPTER 11 Sound and Light
Self Check
1 Compare and contrast opaque transparent and
translucent materials Give one example of each
2 Discuss why you can see your reflection in a smooth
piece of aluminum foil but not in a crumpled ball of foil
3 Infer what happens to light waves that are reflected off
dust particles in the air
4 Explain what happens to white light when it passes
through a prism
5 Think Critically Suppose a material has the same index
of refraction as water How would a light wave change
direction as it traveled from water into this material
Summary
Light and Matter
bull The amount of light that is absorbed
reflected or transmitted depends on the
material making up the object
Reflection of Light
bull Light waves always obey the law of reflection
the angle of incidence equals the angle of
reflection
bull Regular reflection causes parallel light waves
to be reflected in only one direction
bull Diffuse reflection causes parallel light waves
to be reflected in many directions
bull Scattering occurs when light waves are reflected
and travel in many different directions
Refraction of Light
bull Refraction occurs when a light wave changes
speed in moving from one material to another
bull The index of refraction of a material indicates
how much light slows down in the material
6 Find an Angle A light wave strikes a mirror at an
angle of 42deg from the surface of the mirror What
angle does the reflected wave make with the normal
7 Find an Angle A light wave reflects from a mirror at
27deg from the normal What was the angle between
the mirror and the incident wave
Mirages When yoursquore traveling in a car you might see whatlooks like a pool of water on the road ahead As you get closerthe water seems to disappear Yoursquove seen a miragemdashan image ofa distant object produced by the refraction of light through airlayers of different densities Mirages result when the air atground level is much warmer or cooler than the air above asshown in Figure 13 The density of air increases as air cools andlight waves move slower in cooler air than in warmer air As aresult light waves are refracted as they pass through air layerswith different temperatures
Figure 13 Mirages result when
air near the ground is much
warmer or cooler than the air
above This causes light waves
reflected from an object to refract
creating one or more additional
images
MirageWarm air
Cool air
More Section Review gpesciencecom
null
3678031
eng - iTunNORM 00000325 00000000 00002007 00000000 00006053 00000000 00005FC5 00000000 00000082 00000000
SECTION 3 Mirrors Lenses and the Eye 331
Light RaysLight sources send out light waves in all directions These
waves spread out like ripples on the surface of water spread outfrom the point of impact of a pebble You can think of the lightcoming from the source as being many narrow beams of light trav-eling in all directions Each narrow light beam is called a light ray
MirrorsA mirror is any surface that produces a regular reflection A pool
of still water a metal pan and even the back of a shiny spoon can bemirrors Mirrors can be flat curved inward or curved outward
Plane Mirrors A flat smooth mirror is a plane mirror Whenyou look in a plane mirror your image appears upright If youstand 1 m from the mirror your image appears 1 m behind themirror or 2 m from you In fact your image is what a friend stand-ing 2 m from you would see Figure 14 shows how your image isformed First light rays from a light source strike you Every pointthat is struck by the light rays reflects these rays so they travel out-ward in all directions If your friend were looking at you thesereflected light rays coming from you would enter her eyes so shecould see you However if a mirror is placed between you and yourfriend light rays are reflected from the mirror back to your eyes
Mirrors Lenses andthe Eye
Reading Guide
Describe how images are formed
by three types of mirrors Explain how convex and concave
lenses form images Explain how the human eye
enables you to see Describe how lenses are used to
correct vision problems
Mirrors and lenses are used in optical
instruments such as cameras and
telescopes
Review Vocabulary
reflection the process of changing
direction after striking a surface
New Vocabulary
bull plane mirror
bull concave mirror
bull convex mirror
bull convex lens
bull concave lens
Figure 14 Seeing an image of
yourself in a mirror involves two
sets of reflections light rays are
reflected from you and then are
reflected by the mirror
null
8327801
eng - iTunNORM 000002D0 00000000 00002268 00000000 00000153 00000000 00005F17 00000000 0000A000 00000000
332 CHAPTER 11 Sound and Light
Virtual and Real Images The forma-tion of an image by a plane mirror isshown in Figure 15 Your brain assumesthat light rays travel in a straight line As aresult rays that enter your eyes seem tocome from behind the mirror This makesthe image seem to be behind the mirrorHowever no light rays actually passthrough the place where the image seemsto be located This type of image is called avirtual image Plane mirrors always formvirtual images If light rays from an objectpass through the location of the image theimage is called a real image Curved mir-rors can form both real and virtual images
Concave Mirrors If the surface of a mirror is curved inwardit is called a concave mirror as shown in Figure 16 The opticalaxis is an imaginary straight line drawn perpendicular to thesurface of the mirror at its center Every light ray traveling par-allel to the optical axis is reflected through a point on the opti-cal axis called the focal point The distance from the center ofthe mirror to the focal point is called the focal length
The image formed by a concave mirror depends on the loca-tion of the object relative to the focal point Figure 16 shows acandle located more than twice the focal length from the mirrorAlthough many light rays come from each point on the candleonly two rays from the same point are shown Ray A passesthrough the focal point and then reflects off the mirror movingparallel to the optical axis Ray B travels parallel to the opticalaxis before reflecting off the mirror and passing through thefocal point The point where the two rays meet is the location ofthe image of the original point on the candle The image formedis a real image because light rays from the candle pass throughthe place where the image is located
Figure 16 Rays A and B start from the same
place on the candle travel in different directions
and meet again on the reflected image
Diagram how two other points on the image ofthe candle are formed
Figure 15 Your brain interprets
the light rays reflected by the
mirror as coming from a point
behind the mirror
Infer how the size of your imagein a plane mirror depends on yourdistance from the mirror
Focalpoint
Optical axis
Ray B
Ray A
null
10981704
eng - iTunNORM 00000304 00000000 000027B7 00000000 0001942F 00000000 00006076 00000000 00001DB1 00000000
SECTION 3 Mirrors Lenses and the Eye 333
Images Produced by a ConcaveMirror When an object is between oneand two focal lengths from a concavemirror the image is real inverted andlarger than the object An object closerthan one focal length from a concavemirror produces a virtual image that isupright and larger than the object Noimage is produced if the object islocated at the focal point
Convex Mirrors When you are in astore look up toward one of the backcorners or at the end of an aisle to see ifa large rounded mirror is mountedthere You can see a large area of the store in such a mirror Amirror that curves outward like the back of a spoon is called aconvex mirror Light rays that hit a convex mirror diverge orspread apart after they are reflected Figure 17 shows how therays from an object are reflected by a convex mirror to form animage The reflected rays diverge and never meet so a convexmirror forms only a virtual image The image also is upright andsmaller than the actual object is
Describe the image formed by a convex mirror
LensesWhat do your eyes have in common with cameras eyeglasses
and microscopes Each of these contains at least one lens A lens is atransparent object with at least one curved surface that causes lightrays to refract The image that a lens forms depends on the shape ofthe lens Like curved mirrors lenses can be convex or concave
Convex Lenses A convex lens is thicker in the middle than atthe edges Its optical axis is an imaginary straight line that is per-pendicular to the surface of the lens at its thickest point When lightrays approach a convex lens traveling parallel to its opticalaxis the rays are refracted toward the center of the lens asin Figure 18 Light rays traveling along the optical axis arenot bent at all All light rays traveling parallel to the opti-cal axis are refracted so they pass through a single pointwhich is the focal point of the lens The less curved thesides of the lens the less light rays are bent As a resultlenses with flatter sides have longer focal lengths Figure 19
on the next page shows that convex lenses can form eitherreal or virtual images
Figure 18 Convex lenses are
thicker in the middle than at the
edges Light rays that are parallel
to the optical axis are refracted so
that they pass through the focal
point A light ray that passes
through the center of the lens is
not refracted
Figure 17 A convex mirror
forms a reduced upright virtual
image
Optical axis
Ray A
Ray B
Focallength
Focalpoint
null
1415296
eng - iTunNORM 00000307 00000000 000034C4 00000000 0000F329 00000000 000060CF 00000000 000128D6 00000000
Figure 19
VISUALIZING IMAGES FORMED BY A CONVEX LENS
334 CHAPTER 11 Sound and Light
Aconvex lens can form images that are real or virtual enlarged or reduced and upright orinverted Just as for a concave mirror the type of image formed by a convex lens depends on thelocation of the object relative to the focal point of the lens
Optical axis
One
focal
length
Two
focal
lengthsRay B
Image
Ray A
Object
Focal
point
Optical axis
One
focal
length
Two
focal
lengths
Ray B
Ray AObject
Image
Focal
point
Optical axis
Ray B
ObjectRay A
One
focal
length
Focal
pointImage
If the object is more than two focal lengths from the lens the image formed is real inverted andsmaller than the object As the object moves farther from the lens the image becomes smaller
If the object is between one and two focal lengths from the lens the image formed is real invertedand larger than the object As the object moves closer to the focal point the image becomes larger
If the object is less than one focal length from the lens the image is virtual upright and larger thanthe object The image is virtual because the light rays from the object diverge after they pass throughthe lens The image becomes smaller as the object moves closer to the lens
SECTION 3 Mirrors Lenses and the Eye 335
Concave Lenses A concave lens is thinnerin the middle and thicker at the edges Asshown in Figure 20 light rays that passthrough a concave lens bend away from theoptical axis The rays spread out and nevermeet so a real image is never formed Theimage is always virtual upright and smallerthan the object is Concave lenses are used insome types of eyeglasses and some telescopesConcave lenses usually are used in combinationwith other lenses
What type of image is formed by a concave lens
The Human EyeWhat determines how well you can see the words on this
page If you donrsquot need eyeglasses the structure of your eye givesyou the ability to focus on these words and other objects aroundyou Look at Figure 21 Light enters your eye through a trans-parent covering on your eyeball called the cornea The corneacauses light rays to bend so that they converge The light thenpasses through an opening called the pupil Behind the pupil isa flexible convex lens Muscles attached to the lens change itsshape to help focus light forming a sharp image on your retina
The retina is the inner lining of your eye The retina con-tains light-sensitive cells that convert an image into electricalsignals These signals then are carried along the optic nerve toyour brain to be interpreted With this complex structurethe human eye is capable of seeing clearly in bright and dimconditions focusing on both near and far objects and alsodetecting colors
Figure 20 A concave lens
refracts light rays so they spread
out away from the optical axis
Classify Is a concave lens mostlike a concave mirror or a convexmirror
Optical axis
Retina
Focalpoint
Pupil
Cornea
Lens
Optic nerve
Figure 21 The cornea and lens in your eye
bend light rays so that a sharp image is
formed on the retina
Eye Doctors Optometristsand ophthalmologists treatmany different eye prob-lems They often useadvanced technology todiagnose and correct mal-functioning parts of theeye Research an eye prob-lem and how it is treatedWrite a paragraph describ-ing what parts of the eyeare affected by the problemand how doctors correct it
null
9670425
eng - iTunNORM 00000302 00000000 00001E2B 00000000 0000E80A 00000000 00006050 00000000 00000843 00000000
336 CHAPTER 11 Sound and Light
Brightness and Intensity The human eye can adjust to thebrightness of the light that strikes it If you step outside on asunny day you may have to shade your eyes against the intensityof the sunlight Light intensity is the amount of light energy thatstrikes a certain area each second Brightness is the human per-ception of light intensity Sunlight seems bright because a largeamount of light energy strikes your retina each second Youreyes respond to bright light by decreasing the size of your pupilThis reduces the amount of light that enters your eye and strikesthe retina
Intensity depends on your distance from a light source Ifyou move away from a bare lightbulb you can see how theintensity of the light rapidly decreases Because light rays spreadout from the source less light energy strikes your retina thefarther away you are from the bulb
Correcting Vision ProblemsIf you have good vision you should be able to see objects
clearly when they are 25 cm or farther away from your eyes Asharp image of an object should be formed on your retinaHowever for many people the image is blurry or formed in thewrong place causing vision problems
Farsightedness If you can see distant objects clearly butcanrsquot bring nearby objects into focus then you are farsighted Inthis case the eyeball might be too short or the lens isnrsquot curvedenough to form a sharp image of nearby objects on the retinaas shown in Figure 22 To correct the problem convex lensescan be used to bend incoming light rays so they converge beforethey enter the eye
Experimenting withFocal LengthsProcedure1 Complete the safety form
2 Fill a glass test tube with
water and seal it with a
lid or stopper3 Type or print SULFUR
DIOXIDE in capital letters
on a piece of paper4 Set the test tube horizon-
tally over the words
Record your observations
5 Hold the tube at several
heights above the words
Record your observations
Analysis1 Describe how the words
changed as the height of
the test tube increased
2 Classify the image at each
height as real or virtual
Focal
point
Correctedfarsighted eye
Light fromnearby object
Focalpoint
Light fromnearby object
Farsighted eye
The focal length of a farsighted eye is too long to form
a sharp image of nearby objects on the retina
A convex lens in front of a farsighted eye enables a sharp
image of nearby objects to be formed on the retina
Figure 22 Farsightedness can
be corrected by convex lenses
null
9377869
eng - iTunNORM 00000319 00000000 00001DCD 00000000 00002263 00000000 000060F4 00000000 00009CA1 00000000
SECTION 3 Mirrors Lenses and the Eye 337
Self Check
1 Diagram how light rays from an object are reflected by
a convex mirror to form an image
2 Infer how the size of the image changes if an object
that is less than one focal length from a concave mirror
moves closer to the mirror
3 Explain how the focal length of a convex lens changes
as the sides of the lens become less curved
4 Compare the image of an object less than one focal
length from a convex lens with the image of an object
more than two focal lengths from the lens
5 Think Critically Describe the image formed by a light
source placed at the focal point of a convex lens
Summary
Mirrors
bull A plane mirror forms upright virtual images
bull The image formed by a concave mirror
depends on the location of the object relative
to the focal point
bull Convex mirrors always produce virtual upright
images that are smaller than the object
Lenses
bull The image formed by a convex lens depends
on the distance of the object from the lens
bull Concave lenses always form virtual upright
images that are smaller than the object
The Eye and Vision
bull The eye contains a lens that changes shape to
produce sharp images on the retina
bull Farsightedness occurs when the eye cannot
form a sharp image of nearby objects
Nearsightedness occurs when the eye cannot
form sharp images of distant objects
6 Calculate Object Distance If you looked through a
convex lens with a focal length of 15 cm and saw a
real inverted enlarged image what is the maximum
distance between the lens and the object
Nearsightedness If you have nearsighted friends you knowthat they can see only nearby objects clearly Their eyes cannotform a sharp image on the retina of an object that is far awayInstead the image is formed in front of the retina as shown inFigure 23 To correct this problem a nearsighted person canwear concave lenses Figure 23 shows how a concave lens causesincoming light rays from distant objects to diverge before theyreach the eye Then the rays can be focused by the eye to form asharp image on the retina
Figure 23 Nearsightedness can
be corrected with concave lenses
Focalpoint
Light fromdistant object
Nearsighted eye
Focalpoint
Light fromdistant object
Correctednearsighted eye
When a nearsighted person looks at distant objects a
sharp image is formed in front of the retina
A concave lens in front of a nearsighted eye makes light
rays diverge so a sharp image is formed on the retina
More Section Review gpesciencecom
null
31555748
eng - iTunNORM 00000314 00000000 000022F9 00000000 000051A1 00000000 0000600E 00000000 00001B58 00000000
How can you see the back of your head You
can use two mirrors to view a reflection of a
reflection of the back of your head
Real-World ProblemHow many images are seen in two mirrors
Goal Infer how the number of images depends
on the angle between two mirrors
Materialsplane mirrors (2) protractor
masking tape paper clip
Safety Precautions
Handle glass mirrors and paper clips carefully
Procedure1 Complete the safety form
2 Lay one mirror on top of the other with the
mirror surfaces together Tape together one
side so they can open and close Use tape to
label them L and R for left and right
3 Open the mirrors and stand them on a sheet
of paper at an angle of 72deg
4 Bend one leg of a paper clip up 90deg and
place it close to the front of the R mirror
5 Count the number of images of the paper
clip you see in the R and L mirrors Record
these numbers in your data table
6 The mirrors create an image of a circle
divided into wedges Record the number
of wedges
7 Hold the R mirror still and slowly move the Lmirror to 90deg Record the numbers of images
of the clip and wedges in the circle Repeat
this time opening the mirrors to 120deg
Conclude and Apply1 Infer the relationship between the number
of wedges and paper clip images
2 Determine the angle that would divide a
circle into six wedges Hypothesize how
many images would be produced Test your
hypothesis
Reflections of Reflections
Demonstrate for younger students the
relationship between the angle of the
mirrors and the number of reflections
338 CHAPTER 11 Sound and Light
Angle
Number of Number
of Mirrors Paper Clip Images
of Wedges R L
72ordm
90ordm
120ordm
Images and Wedges Seen in the Mirrors
Do not write in this book
SECTION 4 Light and Color 339
Why Objects Have ColorWhy do some apples appear red while others look green or
yellow An objectrsquos color depends on the wavelengths of light itreflects Recall that white light is a blend of all colors of visiblelight When a red apple is struck by white light it reflects redlight back to your eyes and absorbs all of the other colorsFigure 24 shows white light striking a green leaf Only the wave-lengths corresponding to green light are reflected to your eyes
Although some objects appear to be black black isnrsquot acolor Black is the absence of visible light Objects that appearblack absorb all colors of light and reflect little or no light backto your eyes White objects appear to be white because theyreflect all colors of visible light
Why does a white object appear white
Colored Filters Wearing tinted glasses changesthe color of almost everything you see If the lensesare yellow the world takes on a golden glow If theyare rose colored everything looks rosy Somethingsimilar would occur if you placed a colored clearplastic sheet over this white page The paper wouldappear to be the same color as the plastic The plasticsheet and the tinted lenses are filters A filter is atransparent material that transmits one or more col-ors of light but absorbs all others The color of a fil-ter is the color of the light that it transmits
Light and Color
Reading Guide
Explain how you see color Describe the difference between
light color and pigment color Predict what happens when dif-
ferent colors are mixed
From traffic lights to great works of
art color is an important part of your
world
Review Vocabulary
retina inner layer of the eye con-
taining cells that convert light
images into electrical signals
New Vocabulary
bull pigment
Figure 24 This leaf absorbs all
wavelengths of visible light except
the wavelengths you see as green
null
9195021
eng - iTunNORM 00000305 00000000 00001D5D 00000000 000001A1 00000000 00006110 00000000 0000B2AC 00000000
340 CHAPTER 11 Sound and Light
Looking Through Colored Filters Figure 25 shows howthe color of an object can change when you look at it throughvarious colored filters The cooler looks blue under white lightbecause it reflects only the wavelengths of blue light that strikeit If you look at the cooler through a blue filter the cooler stilllooks blue because the blue filter transmits the reflected bluelight However if you look at the cooler through a red filter thecooler seems black because the red filter blocks the blue lightreflected by the cooler
Why does a blue object appear black whenviewed through a red filter
Seeing ColorAs you approach a busy intersection the color of the traffic
light changes from green to yellow to red On the cross street thecolor changes from red to green At a busy intersection trafficsafety depends on your ability to detect color changes rapidlyHow do you see colors
Light and the Eye In a healthy eye light enters the eyethrough the cornea is focused by the lens and finally forms animage on the retina The retina is made up of two types of cellsthat absorb light as shown in Figure 26 When these cellsabsorb light energy chemical reactions convert light energy intonerve impulses that are transmitted to the brain One type ofcell in the retina called a cone enables you to distinguish colorsand detailed shapes of objects Cones need bright light to gener-ate nerve impulses so they do not operate in dim light As aresult even brightly colored objects might look gray or black indim light
Figure 25 The color of this
cooler changes when viewed
through different color filters
Topic Color BlindnessVisit for Web
links to information about the
causes of color blindness
Activity Research the causes
and types of color blindness Find
out how cones are related to the
ability to distinguish colors
gpesciencecom
null
973834
eng - iTunNORM 000002EC 00000000 000021E7 00000000 00014224 00000000 00006123 00000000 000146D6 00000000
SECTION 4 Light and Color 341
Cones and Rods Your eyes have three types of cones each ofwhich responds to a different range of wavelengths Red conesrespond to mostly red and yellow light Green cones respond tomostly yellow and green light Blue cones respond to mostlyblue and violet light The second type of cell in the retina calleda rod is sensitive to dim light and enables you to see at nightHowever rod cells do not enable you to see colors
Interpreting Color Why does a bananalook yellow The light reflected by the
banana causes the cone cells that are sensitive to red and greenlight to send signals to your brain Your brain could get the samesignal if a mixture of red light and green light reached your eyesThis mixture also would cause your red and green cones torespond and you would see the color yellow As a result lightwith wavelengths corresponding to yellow light and light that isa mixture of red and green light both cause the color yellow tobe seen What happens when you look at a white shirt You seewhite when all wavelengths of visible light enters your eyes Thenall three sets of cones cells send signals to the brain The com-bination of these signals cause you to see the shirt as white
Color Blindness If one or more of your sets of cone cellsdo not function properly you might not be able to distinguishcertain colors This condition is called color blindness orcolor deficiency About eight percent of men and one-halfpercent of women have some form of color blindness Themost common form of color blindness makes it difficult todistinguish between red and green Figure 27 shows an imagethat is used in a test for redndashgreen color blindness Becausered and green are used in traffic signals drivers and pedestri-ans must be able to identify them
Retina
Rod
Cone
Lens
Figure 27 Color blindness is an
inherited sex-linked condition in
which certain sets of cones in the
retina do not function properly
Identify the number that you seein the dots
Figure 26 Light enters the eye
and focuses on the retina The two
types of light-detecting cells
that make up the retina
are called rods and cones
null
1070482
eng - iTunNORM 00000340 00000000 00002026 00000000 000155F0 00000000 0000607C 00000000 0000097D 00000000
342 CHAPTER 11 Sound and Light
Mixing ColorsIf you have ever browsed through a paint store you have
probably seen displays where customers can select paint samplesof almost every imaginable color The colors are a result of mix-tures of pigments For example you might have mixed blue andyellow paint to produce green paint A pigment is a coloredmaterial that is used to change the color of other substancesThe color of a pigment results from the different wavelengths oflight that the pigment reflects
Mixing Colored Lights From the glowing orange of a sun-set to the deep blue of a mountain lake all the colors you see canbe made by mixing three colors of light These three colorsmdashred green and bluemdashare the primary colors of light They cor-respond to the three different types of cones in the retina ofyour eye When mixed together in equal amounts they producewhite light as Figure 28 shows Mixing the primary colors indifferent proportions can produce the colors you see
What are the primary colors of light
Paint Pigments If you were to mix equal amounts of redgreen and blue paint would you get white paint If mixing col-ors of paint were like mixing colors of light you would but mix-ing paint is different Paints are made with pigments Pigmentsproduce color as a result of the wavelengths of light they reflectPaint pigments usually are made of chemical compounds suchas titanium oxide a bright white pigment and lead chromatewhich is used for painting yellow lines on highways
Figure 28 White light is pro-
duced when the three primary col-
ors of light are mixed in equal
amounts
Color for PhotosynthesisPlant pigments determinethe wavelengths oflight for photosynthesisLeaves usually look greenbecause of the pigmentchlorophyll Chlorophyllabsorbs most wave-lengths of visible lightexcept green which itreflects However not allplants are green Researchdifferent plant pigmentsto find out how they allowplant species to survive indiverse habitats
null
89129135
eng - iTunNORM 0000026F 00000000 000023FD 00000000 0000C8EB 00000000 00006149 00000000 000059CB 00000000
SECTION 4 Light and Color 343
Self Check
1 Identity what colors are reflected and what colors are
absorbed if a white light shines on a red shirt
2 Discuss how the primary colors of light differ from the
primary pigment colors
3 Explain why a red apple would appear black if you
looked at it through a blue filter
4 Determine why a white fence appears to be white instead
of multicolored if all colors are present in white light
5 Think Critically Light reflected from an object passes
through a green filter then a red filter and finally a
blue filter What color will the object seem to be
Summary
Why Objects Have Color
bull The color of an object is determined by the
wavelengths of light it reflects
bull The color of a filter is the color of the light the
filter transmits
Seeing Color
bull Rod and cone cells are light-sensitive cells
found in the retina of the human eye
bull Rod cells are sensitive to dim light Cone cells
enable colors to be seen
bull There are three types of cone cells One type
responds to red light another to green light
and another to blue light
Mixing Colors
bull Red green and blue are the primary light
colors Any color of light can be created by
mixing these primary light colors
bull Any pigment color can be formed by mixing
the primary pigment colorsmdashmagenta cyan
and yellow
6 Use Percentages In the human eye there are about
120000000 rods If 90000000 rods trigger at once
what percentage of the total number of rods triggered
7 Convert Units The wavelengths of light are measured
in nanometers (nm) which equals 0000001 mm
Find the wavelength in mm of a light wave that has a
wavelength of 690 nm
Mixing Pigments You can make any pigment color by mixingdifferent amounts of the three primary pigmentsmdashmagenta(bluish red) cyan (greenish blue) and yellow In fact color print-ers use these pigments as well as black ink to make full-colorprints like the pages in this book A primary pigmentrsquos colordepends on the wavelengths of the light that it reflects Actuallypigments both absorb and reflect a range of colors in sending asingle color message to your eye For example in white lightyellow pigment appears yellow because it reflects red and greenlight but absorbs the other wavelengths of visible light The colorof a mixture of two primary pigments is determined by theprimary colors of light that both pigments reflect
Look at Figure 29 The area in the center where the colors alloverlap appears to be black because the three blended primarypigments absorb all the primary colors of light Recall that theprimary colors of light combine to produce white light They arecalled additive colors However when the primary pigment col-ors are combined they absorb all wavelengths of visible light andproduce black Because black results from the absence ofreflected light the primary pigments are called subtractive colors
Figure 29 The three primary
pigment colors appear to be black
when they are mixed
Describe how the primary pigmentcolors are similar to the primary col-ors of light
More Section Review gpesciencecom
null
7230715
eng - iTunNORM 000002A9 00000000 00001B2C 00000000 0000E3C1 00000000 00006099 00000000 00004705 00000000
Design Your OwnDesign Your Own
344
Real-World ProblemWhat loud noises do you enjoy and which ones do you find annoying
Most people enjoy a music concert performed by their favorite artist or
the booming displays of fireworks on the Fourth of July Most people
enjoy these loud sounds for short periods of time However certain
other loud noises such as traffic sirens and loud talking can be
annoying Constant annoying noises are called noise pollution What
can be done to reduce noise pollution What types of barriers will best
block out noise pollution
Form a HypothesisBased on your experiences with loud noises form a hypothesis that
predicts the effectiveness of different types of barriers at blocking out
noise pollution
Test Your HypothesisMake a Plan
1 Complete the safety form
2 Decide what type of barriers or materials you will test
3 Describe exactly how you will use these materials
Goals Design an experiment
that tests the effective-
ness of various types of
barriers and materials
for blocking out noise
pollution
Test different types of
materials and barriers
to determine the best
noise blocks
Possible Materialsradio CD player horn
drum or other loud
noise source
shrubs trees concrete
walls brick walls stone
walls wooden fences
parked cars or hanging
laundry
sound meter
meterstick or metric tape
measure
Blocking NfisePollution
4 Identify the controls and variables you will use in your
experiment
5 List the steps you will use and describe each step precisely
6 Prepare a data table in your Science Journal to record your
measurements
7 Organize the steps of your experiment in logical order
Follow Your Plan
1 Ask your teacher to approve your plan and data table before
you start
2 Conduct your experiment as planned
3 Test each barrier two or three times
4 Record the results from each test in your data table in your Science Journal
Analyze Your Data1 Identify the barriers that most effectively reduced noise pollution
2 Identify the barriers that least effectively reduced noise pollution
3 Compare the effective barriers and identify common characteristics that might
explain why they reduced noise pollution
4 Compare the natural barriers you tested with the artificial barriers Which type
of barrier best reduced noise pollution
5 Compare the different types of materials the barriers were made of Which
type of material best reduced noise pollution
Conclude and Apply1 Evaluate whether your results support your hypothesis
2 Predict how your results would differ if you used a louder source of noise such
as a siren
3 Infer from your results how people living near a
busy street could reduce noise pollution
4 Identify major sources of noise pollution in or
near your home How could they be reduced
5 Research how noise pollution can be
unhealthy
LAB 345
Draw a poster illustrating how builders and
landscapers could use certain materials to
better insulate a home or office from excess
noise pollution
346 CHAPTER 11 Sound and Light
A Haiku GardenThe Four Seasons in Poems and Prints
by Stephen Addiss with Fumiko and Akira Yamamoto
Respond to the Reading1 How do the illustrations help the reader
better understand the poems2 What do you think is meant by the
word lingering in the Haiku about springsunlight
3 Linking Science and Writing Writeone haiku about summer and anotherabout fall In one poem use color tohelp you describe the season In theother use light or some property oflight to help describe the season
Research has deter-mined that there is a
connection between color and mood Warmcolors have longer wavelengths and can bemore stimulating Cool colors which haveshorter wavelengths tend to have a calmingor soothing effect on people Light and colorhave long been used as literary symbols Doesthe use of color change what you imaginewhen you read the haiku
UnderstandingLiteratureJapanese Haiku A haiku is a verse thatconsists of three lines and 17 syllables inthe Japanese language The first and thirdlines have five syllables each and themiddle line has seven syllables Why isimagination important in reading haiku
Lingering
in every pool of watermdash
spring sunlightIssa
Withered by winter
the sound of the windmdash
one-color worldBasho
Sound
1 Sound waves are compressional waves thattravel only in matter
2 The speed of sound in a material dependson the type of material as well as itstemperature
3 Loudness depends on a sound waversquos inten-sity Pitch depends on a sound waversquosfrequency
4 Sound waves are used in echolocationsonar and medical imaging
Reflection and Refractionof Light
1 Light can be absorbed reflected or trans-mitted by a material
2 When light waves are reflected theyobey the law of reflectionmdashthe angle ofincidence equals the angle of reflection
3 A light wave is refracted or bent whenit changes speed as it travels at an anglefrom one material to another
Mirrors Lenses andthe Eye
1 Plane mirrors form upright virtual images
2 Images formed by concave mirrors andconvex lenses depend on the location ofthe object relative to the focal point
3 Convex mirrors and concave lenses formvirtual upright images that are smallerthan the object
4 The lens in the human eye changes shape toproduce a sharp image on the retina
Light and Color
1 You see color when light is reflected offobjects and into your eyes
2 Cone cells in the retina are light-sensitivecells that enable you to distinguish colors
3 Red blue and green are the three primarycolors of light and can be mixed to form allother colors
4 The primary pigment colors are magentacyan and yellow
CHAPTER STUDY GUIDE 347
Use the Foldable you made at the beginningof the chapter to help you review sound and light
Interactive Tutor gpesciencecom
Complete each statement with the correctvocabulary word or phrase
1 A change in frequency due to a movingsound source is due to the
2 A flat smooth surface that reflects light andforms an image is a(n)
3 An object is if you can seethrough it clearly
4 The of a material indicates howmuch the speed of light in the materialchanges as light passes through
5 You can change the color of white paint byadding a(n) to it
6 A(n) is a reflecting surface thatcurves outward like the back of a spoon
7 The human perception of the intensity of asound wave is
Choose the word or phrase that best answerseach question
8 Which of the following best describes imageformation by a plane mirrorA) A real image is formed in front of the mirrorB) A real image is formed behind the mirrorC) A virtual image is formed in front of the
mirrorD) A virtual image is formed behind the mirror
9 For a sound with low pitch what else isalso always lowA) amplitude C) wavelengthB) frequency D) wave velocity
10 Which of the following occurs when asound source moves away from youA) The soundrsquos velocity decreasesB) The soundrsquos loudness increasesC) The soundrsquos frequency decreasesD) The soundrsquos frequency increases
Use the table below to answer question 11
11 Based on the data in the table abovewhich of the following would be the speedof sound in air at 30degCA) 3404 ms C) 3494 msB) 3464 ms D) 3534 ms
12 What happens to a light ray travelingparallel to the optical axis of a convexlens that passes through the lensA) It travels parallel to the optical axisB) It passes through the focal pointC) It is bent away from the optical axisD) It forms a virtual image
13 Light waves of which color are bent mostwhen passing through a prismA) blue C) violetB) red D) yellow
14 Which way does a concave lens bend lightA) toward its optical axisB) toward its centerC) toward its edgesD) toward its focal point
Speed of Sound in Air
Temp peed( s)
4
4
4
348 CHAPTER REVIEW
concave lens p 335concave mirror p 332convex lens p 333convex mirror p 333decibel p 322Doppler effect p 323index of refraction p 329intensity p 322
loudness p 322opaque p 327pigment p 342pitch p 323plane mirror p 331translucent p 327transparent p 327
Vocabulary PuzzleMaker gpesciencecom
Use the illustration below to answer question 15
15 Describe how the position of the candlechanged if the image of the candle movedaway from the focal point
16 Apply Acoustic scientists sometimes doresearch in rooms that absorb all soundwaves How could such a room be used tostudy how bats find their food
17 Compare White light passes through atranslucent pane of glass and shines on ashirt Both the translucent glass and theshirt appear green Compare the colors oflight that are absorbed and transmitted bythe glass and the shirt
18 Infer Most mammals including dogs andcats canrsquot see colors Infer how the retinaof a catrsquos eye might be different from theretina of a human eye
19 Determine whether a convex lens could forman image that is enlarged real and upright
20 Infer A car comes to a railroad crossingThe driver hears a trainrsquos whistle and itspitch becomes lower What can beassumed about how the train is moving
21 Compare and contrast the reflection of lightfrom a white wall with a rough surfacewith the reflection of light from a mirror
Optical axis
One
focal
length
Two
focal
lengths
Image
Ray A
Object
Focal
point
Interpreting Graphics 22 Infer why a convex mirror and a concavelens can never produce a real image
23 Predict what color a white shirt wouldappear to be if the light reflected from theshirt passed through a red filter and thenthrough a green filter
24 Explain why windows might begin to rattlewhen an airplane flies overhead
25 Communicate Some people enjoy usingsnowmobiles Others object to the noisethat they make Write a proposal for a pol-icy that seems fair to both groups for theuse of snowmobiles in a state park
CHAPTER REVIEW 349
Use the wave speed equation ν ƒλ to answer
questions 26 and 27
26 Calculate Frequency A sonar pulse has awavelength of 30 cm and a speed inwater of 1500 ms Find its frequency
27 Calculate Wavelength What is the wave-length of a sound wave with a fre-quency of 440 Hz if the speed of soundin air is 340 ms
28 Calculate Angle of Incidence A light ray isreflected from a mirror If the anglebetween the incident ray and thereflected ray is 136deg what is the angleof incidence
29 Determine Object Distance You hold anobject in front of a concave mirror witha focal length of 30 cm If you do notsee a reflected image how far from themirror is the object
30 Calculate Speed The speed of light in avacuum is 300000 kms If the index ofrefraction of water is 133 what is thespeed of light in water
More Chapter Review gpesciencecom
1 Which of the following describes the imageformed by a convex mirror
A enlarged
B inverted
C real
D virtual
Use the figure below to answer question 2
2 Which of the following describes a light raythat passes through the focal point andthen is reflected by the mirror
A It travels parallel to the optical axis
B It forms a real image
C It is reflected back through the focal point
D It forms a virtual image
3 Why does an apple look red
A It reflects red light
B It absorbs red light
C It reflects green and blue light
D It reflects all colors of light except red
Use the figure below to answer questions 4 and 5
4 When the primary colors of light are addedtogether what color appears in area H
A cyan
B magenta
C white
D yellow
5 When the primary colors of light are addedtogether what color appears in area G
A cyan
B magenta
C white
D yellow
6 Which of the following increases as the fre-quency of a sound increases
A amplitude
B intensity
C loudness
D pitch
Red Blue
Green
F
H
G K
Focal pointOptical axis
350 STANDARDIZED TEST PRACTICE
Record your answers on the answer sheet provided by your teacher or on a sheet of paper
STANDARDIZED TEST PRACTICE 351
7 Which of the following parts of the eyeenable you to see colors in bright light
A cone cells
B cornea
C lens
D rod cells
Use the graph below to answer questions 8 and 9
8 Determine how far in centimeters theimage is from the lens when the object is15 centimeters from the lens
9 How far in centimeters is the object fromthe lens when the image distance andobject distance are equal
10 A shirt has stripes that are black and whitein white light If green light shines on thisshirt what colors will the black and whitestripes be
11 If you are on a moving train what hap-pens to the pitch of a crossing bell as youapproach the crossing and then moveaway from the crossing
Use the figure below to answer question 12
12 Describe the vision problem show by thefigure and explain how this vision prob-lem can be corrected
13 Explain why the human eye can see colorsbetter in bright light than in dim light
Image Distance fora Convex Lens
Ima
ge
dis
tan
ce (
cm)
30
25
20
15
10
5 10 15 20 25 30
Object distance (cm)
Standardized Test Practice gpesciencecom
Note Units Read carefully and make note of the units used in
any measurement