CPP U11 Lecture
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Transcript of CPP U11 Lecture
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Light : Color and
RefectionUnit 11 Physics
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Target 1: I can identify and state colorsobserved when mixing colored light, colorsobserved when mixing colored pigments
and what color an object or lter will appearin any color light.
Terms: Color Spectrum, White Light, AdditiePrimary Colors, Complementary Colors,
Su!tractie Primary Colors
Lecture #
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$ntro to Color
To physicists, the colors o% things are not in thesu!stances o% the things themseles
Color is in the eye o% the !eholder and isdetermined !y the %re&uencies o% the lightemitted or refected !y things
The perception o% color depends upon our eye'
!rain system ()ample: *e see a red rose *hen the %re&uency
o% red light reaches our eyes
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Colored Light
+isi!le light is only a small portion o% a !roadspectrum o% electromagnetic *aes
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Color o% the light isdetermined !y its*ae %re&uency
Longest *aelength,lo*est %re&uency isred
Shortest *aelength,highest %re&uency isiolet
Color Light
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White light
White is not a color at all
White is the presence o% the entire spectrum o%
isi!le light -R./0$+2
Colored Light
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lac3 light
lac3 is not a color atall
lac3 is the a!senceo% all light %re&uencies
.!4ects appear !lac3*hen the o!4ect
a!sor!s all isi!lelight %re&uencies
Colored Light
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Color Addition
Colored light can!e mi)ed
5i)ing color light iscalled 6coloraddition7 !ecausethe com!inedcolors are %ormed
!y adding light%rom t*o or morelight sources
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There are # additiveprimary colors:
Red
lue
0reen
When all three colors areadded together, theycreate *hite light
Color Addition
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There are # additivesecondary colors:
/ello* -green 8 red2
5agenta -!lue 8 red2
Cyan -green 8 !lue2
These colors are made !yoerlapping 9 o% theprimary additie colors-green, red, or !lue2
Color Addition
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Complimentary colorsare t*o colors that addtogether to produce *hite
light Remem!er that red,
green, and !lue produce*hite light
lue yello* -red 8 green2
Red cyan -green 8 !lue2
0reen magenta -red 8 !lue2
Color Addition
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Chec3 your Understanding
Suppose that light %rom amagenta spotlight andlight %rom a yello*
spotlight are mi)edtogether, *ill *hite light!e produced; ()plain
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Chec3 your Understanding
redand!lue light
/ello* spotlight> redand greenlight
.!sere the dou!le a!undanceo% red Com!ining the light %romthe magenta and yello*spotlights *ill produce a *hitish'red color ' that is, pin3
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?ilters
?ilters are transparent to and appear the color-s2o% light that they *ill allo* to pass through
A red @lter *ill only allo* red light to pass through
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Chec3 your understanding
$% a magenta @lter is held in %ront o% yello* light,*hat color light *ill pass through; ()plain
What colors o% light *ill a magenta @lter allo* to
pass through; magenta
red
!lue
What colors o% light are present in yello* light;
red
green
The @lter *ill only let the red light through so redlight *ill pass through
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Color Su!traction
ust as colored light can !emi)ed, colored pigment canalso !e mi)ed
5i)ing colored pigments-paint, dyes2 is an entirelydiBerent process %rommi)ing colored light
5i)ing red, green, and !luepaint together does notproduce *hite it produces amur3y grey or muddy !ro*n
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Color Su!traction
Paints and dyes are made o% tinyparticles called pigments
Pigments produce their colors !y
a!sor!ing light o% certain%re&uencies and refecting the lighto% other %re&uencies
5i)ing colored pigments is a called6color su!traction7 !ecause certain
colors are a!sor!ed -su!tracted2 !ythe pigment and all other color arerefected and diBerent colors o%light
We can only see the refected color
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Color Su!traction
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There are # subtractiveprimary colors:
5agenta
/ello*
Cyan
When all three colors areadded together, theycreate !lac3 light
Color Su!traction
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There are # subtractivesecondary colors:
Red
lue
0reen
These colors are made !ymi)ing 9 o% the su!tractieprimary colors -magenta,yello*, or cyan2
Color Su!traction
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Chec3 your understanding
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Chec3 your understanding
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Chec3 your understanding
Why is an apple red;
Apples are red !ecause theycontain red pigments *hich
refects red light -and a!sor!light o% other colors2
What *ill happen i% youshine *hite light -R8082on an apple;
The red is refected, andthe green and !lue are
a!sor!ed
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What *ill happen i% you shine !lue light or yello* light on an apple;
An apple under !lue lightDAn apple under yello* lightD
The apple appears!lac3, !ecause nolight is refected=
The apple appearsred, !ecause redlight is stillrefected=
Chec3 your understanding
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A !anana under cyan lightD
The !ananaappears green=lue light isa!sor!ed and greenis refected
How will a bananaappear under cyanlight?Things to consider:
'What colors ma3e up cyanlight;
'What colors o% light *ill a!anana a!sor!;
'What colors o% light *ill a!anana refect;
Chec3 your understanding
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Lecture #
Target 9: $ can identi%y and state the reasons %orthe color o% the s3y and sun due to diBerentconditions or diBerent times o% day
Terms to 3no*: scattering
l li ht i t t ith
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hy is the sky blue?
Theatmo
sphere
Welcome
to(arth
lue light interacts *ithnitrogen in the atmospherecausing it to EscatterF
A%ter !lue is scattered,
red and green lightremain This ma3es thesun appear yello*,!ecause !lue is missing%rom the *hite light
The light is scattered in alldirections !e%ore reaching youreye, so the s3y appears !lue
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y is the sunset red?
Theatmo
sphere
Welcome
to(arth
?irst !luelight isscattered
Guring a sunset the sun is lo* onthe horiHon, so light has moreatmosphere to trael through
Since there is so muchatmosphere to traelthrough, ne)t greenlight also getsscattered=
Red light remains %or a!eauti%ul sunset=
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Lecture IJ
Target #
$ can accurately measure and dra* angles o% incidenceand refection and use ray diagrams to predict the
path light ta3es *hen refected
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What is refection;
When a *ae reaches a !oundary !et*een t*omedia, usually some or all o% the *ae !ounces!ac3 into the @rst medium
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Law of Reflection
angle of incidence =
angle of reflection
The angle is ALWAYSmeasured between the
ray and the normal
Label each term onyour diagram as
shown in the animation
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Test your 3no*ledge I1
Light %rom afashlight shines on amirror andilluminates one o%the cards Gra* therefected !eam toindicate theilluminated card
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Test your 3no*ledge I9
A periscope has a
pair o% mirrors in itGra* the light path%rom the o!4ect . tothe eye o% theo!serer
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What is a irtual image;
Giscoer= Where is your 5irror $mage;
Light al*ays seems to trael %rom straight aheado% us
There%ore *e P(RC($+( o!4ects to !e located!ehind the mirror
A irtual image is an image that appears to !e in
a location *here light does not really reach
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Plane 5irrors
Plane mirrors -fat mirrors2 onlyproduce irtual images
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Test your 3no*ledge I#
The ray diagram !elo* sho*s thee)tension o% one o% the refected rays%rom the plane mirror
Complete the diagram !y -12 care%ullydra*ing the three other refected rays,and -92 e)tending them !ehind the
mirror to locate the image o% the fame-Assume the candle and image are
ie*ed !y an o!serer on the le%t2
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Test your 3no*ledge IJ
Kere *e hae eightstudents in %ront o% asmall plane mirror Their
positions are sho*n inthe diagram !elo*5a3e appropriate raydiagrams to ans*er the%ollo*ing:
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Test your3no*ledge I
Karry Kotshot ie*s himsel% in a %ull'lengthmirror -right2 Construct straight lines %rom
KarryFs eyes to the image o% his %eet andto the top o% his head 5ar3 the mirror to
indicate the minimum area Karry uses tosee a %ull ie* o% himsel%
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Test your3no*ledge I
Goes it matterho* %ar a*ay
he stands;
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Lecture I
Target J : $ can identi%y an descri!e the imageseen in a plane, cone) and concae mirror
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Plane mirrors produce irtualimages
A virtual image is an image thatappears to !e in a location *herelight does not really reach
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Plane 5irror $mages
Plane mirror images al*aysappear
Right Side Up -RSU2 The same siHe as the o!4ect
The same distance a*ay %rom
the mirror as the o!4ect
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Concae 5irrors -Conerging2
$n a concae mirror asthe light comes in it*ill refect andconerge
Where the light comestogether, an image *ill%orm, this can happenin %ront o% or !ehindthe mirror
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Concae 5irrors ' $mages
$% the o!4ect is !e%ore the %ocal point: -IM'N2
O Upright O +irtual O igger
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Concae 5irrors ' $mages
$% the o!4ect is at the %ocal point: -I2
O
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Concae 5irrors ' $mages
$% the o!4ect is !eyond the %ocal point:
O $nertedQ Upside Go*n -USG2 O Real -can shine on a screen2
et*een C and ? $00(R -J'2, At C SA5( S$( -#2, eyond C S5ALL -1'92
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Gierging5irror
Cone) 5irrorsA cone) mirror cures out*ard- Light that hits the mirror %rom a single source
*ill come in and refect the light in directionsthat spread a*ay %rom each other
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Cone) 5irrors-Continued2
The image:
Since the light raysdiverge, they will never
meet in front of themirror, this creates avirtual image behindthe mirror
!pright
"educed in Si#e$Smaller than theoriginal ob%ect&
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Which 5irror Gid $t;