Light travels in a STRAIGHT LINE ANOTHER WAY TO THINK OF LIGHT Light leaving the candle travels in all directions but we only SEE the light that travels in to our EyeBrain ANOTHER WAY TO THINK OF ID: 784268
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Slide1
Geometric Optics
Geometric Optics: The process of using light rays to determine how light behaves when it strikes an object.
Light travels in a STRAIGHT LINE
Slide2ANOTHER WAY TO THINK OF LIGHT
Light leaving the candle travels in all directions, but we only SEE the light that travels in to our Eye-Brain
Slide3ANOTHER WAY TO THINK OF
LIGHT (CONT’D)
We don’t see light that doesn’t enter our eyes.
Slide4ANOTHER WAY TO THINK OF LIGHT (CONT’D)
If the light going away from eyes is reflected in to our Eye-Brain, then we will see it.
Slide5SIDE NOTE
When we look at diagrams, we will ignore light that doesn’t enter our Eye-Brain.
Don’t forget that the other light exists, we are just ignoring it to simplify our lives!
Slide6RAYS & DIAGRAMS
Ray Diagrams
show how light moves from the object to the eye.
Light Ray –
a line on a diagram representing the direction and path that light is travelling.
Slide7LUMINOUS SOURCES
Atoms in
LUMINOUS OBJECTS
emit light rays in all directions produced from other energy sources.
Atoms in
NON-LUMINOUS OBJECTS
scatter the light rays from luminous objects in all
directions.
Slide8NOTE
Atoms in all objects produce or scatter light rays.
This diagram only shows light rays from atoms at the top and bottom of the objects.
Slide9KEEP IT SIMPLE
To make diagrams simpler, we only show one ray of light from the top and bottom of objects.
We simplify it even more and just show only the rays coming from the top of the object.
Slide10MEDIUMS
A
TRANSPARENT MEDIUM allows nearly all rays to pass straight through unaltered. (Ex. Air)
An OPAQUE MEDIUM
absorbs or scatters all the rays. (Ex. Textbook, wall, etc.)
Slide11MEDIUMS (CONT’D)
A
TRANSLUCENT MEDIUM transmits and scatters the rays. Wax paper causes light rays to bounce off and scatter, so you can see light coming through but no clear image.
Slide12The Laws of Reflection
Slide13Reflection -
Images in Plane Mirrors
Slide14a mirror.
calm water surface.
a piece of shiny metal wall.
a piece of window glass.
Where can we see an image of ourselves?
Slide15What are mirrors?
A mirror is any polished surface that allows an image to be produced through reflection. An
image
is a reproduction of the original object in front of the mirror that is produced through the use of light.
Slide16Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
Slide17Properties of Light that Lead to Reflection
Light reflects off of
ALL surfacesA beam of light can be thought of as a group of individual rays of light all travelling together
Slide18Laws of Reflection Investigation
Page 482
Slide19The Two Laws of Reflection
Slide20LAW #1
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
the same
angle it hits it.
normal
incident ray
reflected ray
mirror
Slide21LAW #2
The incident ray, the reflected ray, and the normal all lie in the same plane.
Slide22Question 1
The angle between an incident ray and the mirror is 20
.
The angles of incidence and reflection are ____
and
____
.
20
Slide23Question 1
The angle between an incident ray and the mirror is 20
.
The angles of incidence and reflection are ____
and
____
.
20
70
70
Slide24P.O.E
Predict!
Will there be a difference if I shine light off of a smooth piece of aluminum foil compared to if I shine light off a crumpled piece of aluminum foil?
VS
Slide25P.O.E
Observe!
Slide26P.O.E
Explain!
This can be explained with the terms
specular
reflection
and
diffuse reflection!
Slide27parallel
incident rays
parallel
reflected rays
Specular
Reflection
Light reflects off a smooth, shiny surface
Examples: plane mirror, still water, smooth piece of aluminum foil
Produces a clear reflection
Slide28parallel
incident rays
reflected rays
in different directions
Diffuse Reflection
Light reflects off a rough, not perfectly smooth surface
Examples: cover of a book, waves, a crumpled piece of aluminum foil
Produces a diffuse (unclear) reflection
Slide29True or False?
Reflection of light by a rough surface does not obey the 2 laws of reflection.
Does the angle of incidence = angle of reflection?
Does the incident ray, normal, and reflected ray lie in the same plane?
Slide30True or
False
?
Reflection of light by a rough surface does not obey the 2 laws of reflection.
Does the angle of incidence = angle of reflection?
Does the incident ray, normal, and reflected ray lie in the same plane?
Slide31Even in diffuse reflections, each incident ray is reflected back at the same angle it strikes the object!
Angle of incidence = Angle of reflection
Additional example:
Textbook page 485
Figure 5
Slide32Specular Reflection
A
specular reflection is reflection off a smooth surfaceThe light bounces off in a predictable and consistent way
Slide33Specular Reflection
A
specular reflection is reflection off a smooth surfaceThe light bounces off in a predictable and consistent way
Slide34Diffuse Reflection
A
diffuse reflection occurs off a surface that is not smoothLight rays are scattered and reflect in many different directions
Even microscopically rough surfaces will produce this effect
Slide35Diffuse Reflection
A
diffuse reflection occurs off a surface that is not smoothLight rays are scattered and reflect in many different directions
Even microscopically rough surfaces will produce this effect
Slide36Slide37Types of Mirrors
Plane Mirrors
Parabolic (curved) Mirrors
Slide38Properties of Plane Mirrors
The image is right-side-up (not inverted)
Left and right are reversedThe image is the same size as the object (unmagnified)Light reflects with the properties of angles discovered earlier this class
Slide39Challenge Question:
Which of these appears on the front of an ambulance?
Slide40The writing on an ambulance is reversed because…
The image in a plane mirror is
reversed
Therefore,
this is what we see when we look in the rearview mirror
Slide41More examples…
Slide42Question
What letters of the alphabet will appear the same in a plane mirror?
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Slide43Question
What letters of the alphabet will appear the same in a plane mirror?
A
B C D E F G
H I
J K L
M
N
O
P Q R S
T
U V W X Y
Z
Slide44Using Light Rays to Locate an Image
We know that light travels in straight lines!
Our brain doesn’t understand that light reflects
When our eyes detect reflected light from a plane mirror, we project these rays backwards in a straight line
Slide45Source and Apparent Source
Light Source
Apparent Light
Source
Virtual rays are shown using dotted lines
Slide46Using Equal Perpendicular Lines to Locate an Image
Two Helpful Hints:
The distance from the object to the mirror is the same as the distance from the image to the mirror
If the tip of the pencil is 3 cm away from the mirror, the reflection of image will also be 3 cm away
3 cm
3 cm
2.7 cm
2.7 cm
Slide47Using Equal Perpendicular Lines to Locate an Image
Two Helpful Hints:
The object-image line is perpendicular to the mirror surface
Slide48Diagram
O
I
N
M
The Ray Diagram shows that:
ON = IN
OI ⊥NM
Slide49Locating Images
So how do we draw ray diagrams?
Slide50Drawing the virtual image
Step One:
Choose several points on the object and draw a perpendicular line to the mirror
Slide51Drawing the virtual image
Step Two
Measure the distance of this line
1 cm
1.5 cm
2 cm
Slide52Drawing the virtual image
Step Three
Extend this line an equal distance behind the mirror
1 cm
1.5 cm
2 cm
Slide53Drawing the virtual image
Step Four
Repeat these steps until you have enough lines to accurately locate your image
1 cm
1.5 cm
2 cm
Virtual image
= an image in which light does not actually arrive at
Slide54Drawing the virtual image
Step Five
Draw in the reflected ray
1 cm
1.5 cm
2 cm
Virtual image
= an image in which light does not actually arrive at
Slide55Drawing the virtual image
Step Five
Draw in the incident ray
1 cm
1.5 cm
2 cm
Virtual image
= an image in which light does not actually arrive at
Slide56Practice Question 1
Mirror
Slide57Practice Question 1
Mirror
Slide58Practice Question 2
Mirror
Slide59Practice Question 2
Mirror
Slide60Going back to the beginning…
Slide61Four Characteristics of an Image
SALT
But….
How are we suppose to remember this?
Slide62S stands for SIZE
What is the size of the object?
Larger, Smaller, or the Same Size as the object?
LARGER
SAME
SMALLER
Slide63A stands for ATTITUDE
How is the image oriented?
Is the image upright or inverted?
UPRIGHT
INVERTED
Slide64L stands for LOCATION
Is the image in front or behind the mirror?
Is the length from the object to mirror the same as the image to mirror?
?
Slide65T stands for TYPE
Is the image real or virtual?
VIRTUAL
REAL
A real image is formed when light is actually arriving at the image location
A virtual image is formed from an apparent light source
Slide66Question:
What is the SALT for plane mirrors?
Same Size
Upright
Behind the Mirror
(the same distance behind)
Virtual