Refraction and Lenses
Discover Activity
Reading Preview
Key Concepts
• Why do 1i9h1 raI'S bend wken
they Mte< a Ill@diumalan
angle?
·What~w~oI
.....,
irI'woges lao 11M bot «>nW" iO'ld
~
How Can You Make an Image Appear?
1. Stand about 2 meters from il window. Hold. hand Ie~ up to
'f'OlW eye and Iooll; through it. What do you we? CAUTION; Do
nor look at ~ wn.
2. MoYe the ~ fillthef away from your eye. What d'.nges do
you notice?
3. Now hold the lem bel..een thewindgw OInd iI shl!('1
of paper, but vel'Y dow to lhe~. Slowly moYe
the lens away from the pa~
al'ld toward the window. Kel!p
watching the paper, What do
you ~ 1 YAwl haPPffi~ M yoo
Key Terms
....
• index of ,..n<Ktion
o mi• •
• ~"""". !em
• mnc_lens
move the lem?
~ Target Re.ding Skill
Think
Asking QuKtlons ~fOfe)'OU
~~. pt~ tlw 'N hNdlng5. In
• gr~ Ofgani,le< Iil<e the _
below; W: a wn.t. ~~ ..
how queuion for each Mading.
As you .ud, _ile the arnwen
to j'OUI qvl'StiofK.
-
tto-.
Observing How ~ iHl image
fDfmed on a sheet of paper? Des<ribe the
image. b it real Df Yinu.I? How do you know?
A fuh tank un play tricks on you. If you look through the side
of a fish tank. a fish seems doser lhan if you look over the lOp.
If you look through the corner, you n13Y sec the same fish
Iwict'. You see one imal!ie of the fish throui!;h Ihe frunt of the
lank and anotht'r through Ihe side. The ....,o illlages appt"ar in
diff~nl places! "low can this hap~?
FtlitM[ t3
Optical .usion in 10 Fish Tilnk
There is only one fish in this ~nk..
but r ~ rrvk... it look ~
though then iIl1I! _
ChlOpter 4 0 • 119
Index 01 R.fr~don
Bending light
The index of relriKtion of a medium is a
mea lure of how much light ~n<k ""it travels
from ai, into the medium. 1hfo table.hows the
index of refriKtion of loOI'I"Ie common medium,;.
1. Interpreting Dau, Whid> medium uuses the
gre;rtest dlange in thfo direction of a ~ghl r<l'f1
Z. Interpreting Data According to the t.lble,
which tencls 10 bend light more: solids Of
liquids?
3. Predicting Would you expect light to bend if
II entered (Orn oil at an angle after traveling
through glyl::ero17 Explain.
Water (liquid)
Ethylakohol (liquid)
Quilrn: (loIid)
±
---='00"------1
1.33
'c.,=''--__,
__
1.46
Corn oil (liquid)
c1.47
Glycerol (liquid)
1.47
Glass. ([own (soUd)
1.52
Sodium chloride (solid)
C'""'--__-I
r'=;'='~=(=~c"'''---Diamond (solid)
I
10--_--"'·'=,'---_
2.42
Refraction of Light
FlGUllf 14
Refrl<tion of light
As li9hl pas.... Irom ill Ie.. ~nse
medlom into a more dense
medium, it lolows down and Is
'efraoecl.
120 • 0
RclTaClion can cau~ you to M:C something that may not actu­
ally be there. As you look at a fish ill a tank, the light coming
frolll the fish to your eye bends as it passes through thr« dif­
ferent mediums. The mediums are water, the g1aM; of the tank,
and air. As the light pust'S from one medium to the next.
it refraCls. When light rays enler a medium at an angle. the
change in speW causes the ray.s 10 bend, or change direction.
Refraction in Different Mediums Some Illediums cause
light to bend more than others, as shown in Figure 14. When
light passes from air into water, the light slows down. Light
slows down ewn more when it passes from water into glass.
When light passe.s from glass back into air, the light speeds up.
Light travels fastesl in air, a liule slower in w:lter, and .slower
.still in glass. Notice: that the rolY that leaves the glass is tra"ding
in the s:a.rne dire<lion as it was before it entered the water.
Glass causes light to bend more than either air or water.
Another way to say this is that glass has a higher ind~x of refrac­
tion than either air or W,lter. A material'.s index of refraetion is
a measure of how much a ray of light bends when il enters that
material. The higher the index of refraClion of a medium, the
more it bend.s light. The index of refraction of walCT is 1.33, and
the index of refraction of glass is about 1.5. So ligltl is bent more
by glass lhan by Woller.
Prisms and Rainbows Recall that when white light enlns a
prism, each w,wdenglh is refracled by a different amounl. The
longer lhe wavelenglh, the less lhe wave is bent by a prism. Red,
with the loogelit wavelength, is refracted the least. Violet, wilh
the shortClil: w;wdenglh, is refracted the most. This diffclcnct" in
refraction causes whitl" light 10 spread out into the colors of the
'p<ct~-rcd, orange, yellow, green, hlue, and \·iolet.
The same process occurs in water droplets suspended in thc
air. When white light from the sun shines through the droplets,
a rainbow may appear. The water droplets act like tiny prisms,
refracting and reflecling the light and separating the colors.
Mirages You're trawling in a car on a hot day, and you notice
that lhe road ahead looks wet. Yet when you get there, Ihe road
is dry. Did the puddles dry up? No, the puddleli were never
there! You saw a mirage (mih RAllJ}---an image of a distant
object caused by refraction of light. Tbe puddles on the road
are lighl rays from the sky that are refracted to your eyes.
Figure 16 shows a miragc. NOlice the shiny white areas on
the road bchind the white (ar. The air just abol't' the road is
hotter than the air higher up. Lighltnl\·e1s faster in hot air. So,
lighl rays from the white C"M that travel toward thc road arc
bent upward by Ihe hot air. Your brain assumes lhal the rays
travdtxi in a straight line. So the rays look as if they ha\'e
reflected off a smooth surface. "''hal )'00 see is a mirage.
~R••~;;;·"~,.) What cause<l a mirage 1
flGtHlf
16
Mlr~
The puddles and white reflections on 1he
road tire mlr~. Light refr;M;ts iI'll1 9"'"
from hot air 10 (<.>01 air. The refr<Kted light
~rorometrom_~
Rainbows
""'"
" for""
A raintxwh<.n ...nlight
is refracted and reflC'(ted by liny
water droplets. Observin.g IM>ar
h the ",der o( colon; in a
rajnbow~
..... "
Convex end ConuoVIt lenS115
A convexlemGtfl focus parallel
fays at a local point. A Con<.o1ve I"",
rllUSf'S parallel rays 10 spl'ead apart.
lenses
AnYlinlt~ you
look through binoculars, iii cnmera, or eYeW3sscs,
you aft using lenses to bend light, A lens is a curved piece of
glass or other transparent malerialiltal is used 10 refracllighl.
A lens forms an image by refracting light rays IItal pass through
it. Like mirrors. knsn can ha\"c diITl"rl"nt shapes. The type' of
image formed by a lens dep.ends on lite shape of the lens and
the position of the object.
Convell Lenses A conwx lens is thicker in the center than
al lhe edges. As light rays paral1d 10 the opliol axis pass
through iii COllvtX lens, they are bo!'nl toward the Cl!llh."r of the
lens. The ra)'li meet at lh... focal point of the lens and continue
to travel beyond. The more (urI'cd the lens, the more it refracts
light. A CQnvex lens acts somewhat like a conca\"(: mirror.
b«ausc it focuses rays nflight.
An object's position rclatiYl~ to the focal point determines
whether a convex lens forms a real image or a virtual image.
Figure III shows thai if the ohject is farther away Ihan Ihe focal
point. lhe rcfrOCIoo rays form a ((",11 image on lhe other side of
the lens. If the obj«t is bm-.oeen lhe lens and the focal point, a
virlUilI image forms on lhe same side of Ihe lens as Ihe object.
FlGUIll 1.
Im;tg~;n (onYI!~ ltn""
The type of ima9O! lorrMd by
a c~~ Iern depl!'O<h on lhe
obj~" p<»ition.
focal
,,","
:.t"
Reallma9t 11 the obje<l is lanher from the lem
the focal point. a real image forms.
t~n
Image
Focal
point
the objK1 i\ closoer to the If!,m
lhan the 1(KiII point, a virlUlI' image forms.
yj"uallmag~ If
/
fIGURE 19
Images in Concave ten~
_____________r===~__
Object
A (on<:ave lern prodlK<"S virtual
imag ... that are upright .100
smaller than the obje<t.
--------------
Focal
point
''''''
Interpreting Diagrams Whyciln
a concave lern only form a yirtual
imag<!?
/
ViRua'. Reduced Image Wherever the
object is p11Ked, a virtual image for"",
Go.nline
active,-ar:~
Concave Lenses A concave lens is thinner in the Ct'lller than
at the edges. When light rays traveling par-llIe! to the optical axis
pass through a concave lens, they bend awar from the optical
axis and nl"'''' meet. A concave lens can produce only viclual
images because paraUcllight rays passing through the lens
For.
~
activity
Visit: PIlSdlool,COOl
web Code: co;p-504l
DCl'cr meet.
rigure 19 shows how an image forms in a concave lens. The
virtual image is locatl"d where the light rays appear to come
from. The image is always upright and smaller than the object.
=''::''\1) What;'; the '>hap<! of a concave lens?
S.,tion
3 Assessment
~Target Reading Skill Asking Questions
USt the answt'rs 10 the questions you wrOle
about the lU'adings 10 hdp you allswer the
questions below.
Reviewing Key Concepts
1. 3. Identifying What is a material's imkx of
rcfUClion?
b. Relating Cause (md Effe<l What cau~5light
rays to bend wh<:n Ill")' enter a neW mooiulll
at an angkl
c. Predicting If a glass pri~m were plao:d in
a medium such as water, would i\ separate
white light imo different COIOTS? bpla;n.
2. 3. Defining What is a lens?
b. Comparing and Contrasting Dcsc;ribc the
.hap·c!> of a COllc-a\"\: lens and a com."" lens.
c. Interpreting Diagrams US(' Figu.... 18 to explain
how you milieU wh('lhcr a coo\,{'X!cns will form
a ,(,"31 or virtual image.
At-Home Activity
Bent Pencil Here's how you can bend a pencil
without tOlKhing it. Put a pendl in a gloM of
wilter w thilt it is hillf in ilod hillf out of the
wilter. Hilve your filmily member~ look ilt the
perKil from the ~ide. U~ing your undef'llaoding
of refril(\ion, explain to your family why the
pen<:il ilppeilf'l il~ it does.
Chapter 4 0 • 12]