Light rays

Description of how light rays react

1. Light and Rays

2. ReflectionandRefraction
 :
KeyQuestion
How do we describe the
reflection and refraction
of light?

3. ReflectionandRefraction

The overallstudy ofhow lightbehaves is

called optics
.

The branch ofoptics thatfocuses on the creation of

images is called

geometric optics
,
because itis based

on relationships between angles and lines that
.
describe lightrays

4. ReflectionandRefraction

A
lens
is an opticaldevice

thatis used to bend light
.
in a specific way

A

converging lens

bends

lightso thatthe lightrays
.
come togetherto a point

A

diverging lens

bends

lightso itspreads light

apartinstead ofcoming
.
together

5. ReflectionandRefraction
Mirrors .
reflectlightand allow us to see ourselves

A
prism
is anotheropticaldevice thatcan cause lightto
.
change directions

Aprism is a solid piece ofglass with flatpolished
.
surfaces

6. Reflection
Images
appearin mirrors

because ofhow lightis
.
reflected by mirrors
The
incidentray

follows the
.
lightfalling onto the mirror

The

reflected ray

follows the
.
lightbouncing offthe mirror

7. Reflection

In

specularreflection

each incidentray bounces offin
.
a single direction

Asurface thatis notshiny creates

diffuse reflection
.
 ,
In diffuse reflection a single ray oflightscatters into
.
many directions

8. LawofReflection
The angle of
incidence
equals the
angle of
reflection.
The incident ray
strikes the
mirror.
The reflected ray
bounces off.

9. Lawofreflection
 30
Alightray is incidenton a plane mirrorwith a
.
degree angle ofincidence

Sketch the incidentand reflected rays and determine
.
the angle ofreflection
30
o
30
o

10. Refraction

Lightrays may bend as

they cross a boundary

from one materialto
,
another like from airto
.
water

This bending oflightrays

is known as
.
refraction

The lightrays from the
(
straw are refracted or
)
bent when they cross from

waterbackinto airbefore
.
reaching youreyes

11. Refraction
,
When a ray oflightcrosses from one materialto another

the amountitbends depends on the difference in index
.
ofrefraction between the two materials

12. Indexofrefraction

The ability ofa materialto bend rays oflightis

described by the

index ofrefraction
(n).

14. Calculatetheangleofrefraction

Aray oflighttraveling

through airis incidenton

a smooth surface ofwater
30
atan angle of °to the
.
normal

Calculate the angle of

refraction forthe ray as it
.
enters the water

16. Dispersionandprisms
When white light passes through a glass prism,
blue is bent more than red.
Colors between blue and red are bent proportional
to their position in the spectrum.

17. Dispersionandprisms

The variation in refractive

index with coloris called
dispersion.

Arainbow is an example
.
ofdispersion in nature

Tiny rain droplets actas

prisms separating the

colors in the white light
.
rays from the sun

18. , ,
Mirrors Lenses andImages
:
KeyQuestion
How does a lens or
mirror form an image?

19. , ,
Mirrors Lenses andImages
We see a world of images created on the retina of
the eye by the lens in the front of the eye.

20. , ,
Mirrors Lenses andImages
Objects are real
physical things that
give off or reflect light
rays.
Images are “pictures” of
objects that are formed
in space where light
rays meet.

21. , ,
Mirrors Lenses andImages

The mostcommon image we see every day is ourown
.
reflection in a mirror

The image in a mirroris called a virtualimage because

the lightrays do not
actually .
come together
The virtual image in a flat
mirror is created by the eye
and brain.

22. , ,
Mirrors Lenses andImages

Lightrays thatentera converging lens parallelto its

axis bend to meetata pointcalled the

focalpoint
.

The distance from the centerofthe lens to the focal

pointis called the

focallength
.

The

opticalaxis

usually goes through the centerofthe
.
lens

24. Theimageformedbyalens

Alens can form a
virtual .
image justas a mirrordoes

Rays from the same pointon an objectare bentby the

lens so thatthey
appear
to come from a much larger
.
object

25. Theimageformedbyalens

Aconverging lens can also form a
real .
image
 ,
In a realimage lightrays from the object
actually
come
.
backtogether

26. Drawingraydiagrams

Aray diagram is the bestway to understand whattype
,
ofimage is formed by a lens and whetherthe image is
.
magnified orinverted

These three rays follow the rules forhow lightrays are
:
bentby the lens
1.
Alightray passing through the centerofthe lens is
( ).
notdeflected atall A
2.
Alightray parallelto the axis passes through the far
( ).
focalpoint B
3.
Alightray passing through the nearfocalpoint
( ).
emerges parallelto the axis C

29. OpticalSystems
:
KeyQuestion
How are the properties of
images determine?

30. 
An

opticalsystem
, ,
is a collection ofmirrors lenses
,
prisms orotheropticalelements thatperforms a useful
.
function with light
 :
Characteristics ofopticalsystems are
— , , .
The location type and magnification ofthe image
— .
The amountoflightthatis collected
— ,
The accuracy ofthe image in terms ofsharpness
, .
color and distortion
— ,
The ability to change the image like a telephoto lens
.
on a camera
—
The ability to record the image on film or
.
electronically

OpticalSystems

31. Thesharpnessofanimage
Defects in the image are called aberrations and
can come from several sources.
—Chromatic aberration is caused by dispersion, when
different colors focus at different distances from the
lens.

32. Thesharpnessofanimage
—Spherical aberration causes a blurry image
because light rays farther from the axis focus to a
different point than rays near the axis.

33. Thesharpnessofanimage
—Diffraction causes a point on an object to focus as a
series of concentric rings around a bright spot.

34. Thinlensformula
The thin lens formula is a mathematical way to
do ray diagrams with algebra instead of drawing
lines on graph paper.
1 + 1 = 1
d
o
d
i
d
f
focal
length (cm)
Image distance
(cm)
Object
distance
(cm)

35. Usethethinlensformula
 6
Calculate the location ofthe image ifthe objectis cm
4
in frontofa converging lens with a focallength of
.
cm

36. Imagerelay

Atechnique known as

image relay

is used to analyze
.
an opticalsystem made oftwo ormore lenses

37. :
Application TheTelescope