CPP U11 Lecture

7/23/2019 CPP U11 Lecture

1/49

Light : Color and

RefectionUnit 11 Physics


2/49

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 #


3/49

$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


4/49

Colored Light

+isi!le light is only a small portion o% a !roadspectrum o% electromagnetic *aes


5/49

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


6/49

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


7/49

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


8/49

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


9/49

There are # additiveprimary colors:

Red

lue

0reen

When all three colors areadded together, theycreate *hite light

Color Addition


10/49

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


11/49

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


12/49

Chec3 your Understanding

Suppose that light %rom amagenta spotlight andlight %rom a yello*

spotlight are mi)edtogether, *ill *hite light!e produced; ()plain


13/49

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


14/49

?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


15/49

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


16/49

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


17/49

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


18/49

Color Su!traction


19/49

There are # subtractiveprimary colors:

5agenta

/ello*

Cyan

When all three colors areadded together, theycreate !lac3 light

Color Su!traction


20/49

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


21/49



22/49



23/49


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


24/49

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=



25/49

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;



26/49

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


27/49

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


28/49

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=


29/49

Lecture IJ

Target #

$ can accurately measure and dra* angles o% incidenceand refection and use ray diagrams to predict the

path light ta3es *hen refected


30/49

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


31/49

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


32/49

Test your 3no*ledge I1

Light %rom afashlight shines on amirror andilluminates one o%the cards Gra* therefected !eam toindicate theilluminated card


33/49

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


34/49

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


35/49

Plane 5irrors

Plane mirrors -fat mirrors2 onlyproduce irtual images


36/49

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


37/49

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:


38/49

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%


39/49

Test your3no*ledge I

Goes it matterho* %ar a*ay

he stands;


40/49

Lecture I

Target J : $ can identi%y an descri!e the imageseen in a plane, cone) and concae mirror


41/49

Plane mirrors produce irtualimages

A virtual image is an image thatappears to !e in a location *herelight does not really reach


42/49

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


43/49

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


44/49

Concae 5irrors ' $mages

$% the o!4ect is !e%ore the %ocal point: -IM'N2

O Upright O +irtual O igger


45/49


$% the o!4ect is at the %ocal point: -I2

O


46/49


$% 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


47/49

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


48/49

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&


49/49

Which 5irror Gid $t;

Documents

CPP U11 Lecture