Physics
Light and Geometric Optics
What is Light?
• If you had an alien friend come
visit you on Earth, how would
you describe light? Explain
light? What is light?!
What is Light?
•
Light is a form of energy
that is visible to the human eye.
It can be described:
i) As electromagnetic waves
ii) As particles of light called photons
Light is a wave that
travels in a straight line…
Draw
how
light
travels:
We only see objects if light
reflects off of it.
We can only see the light
if there are dust or smoke
particles in the air.
(i.e. laser show)
We see the absence of
light as shadows.
SAY WHAT?!
Rectilinear
Propagation
SAY THAT AGAIN?!
Rectilinear Propagation
• Why do shadows form?
• Shadow simulator
• Why do eclipses occur?
• Both of these phenomena are a
result of rectilinear propagation...
The simple fact that light must
always travel in straight lines.
Shadows and Eclipses
• Solar eclipses occur when the moon comes
directly between the sun and the Earth.
• The region of the umbra (the darkest
shadow) is left in total darkness.
Light Waves
• Light waves contain both
electric and magnetic fields
• Because light has both
electric and magnetic fields,
it is also referred to as
electromagnetic radiation
Through space!
What does it
Travel through?
Light = energy = waves
= light waves
Light
= Electric=& magnetic waves
= Electromagnetic
waves
Electromagnetic
radiation
Properties
of Waves
• Crest: highest point on a wave
• Trough: lowest point on a wave
• Rest Position: level that there are no waves
• Amplitude: height from the rest position to the highest
point on a crest or lowest point on a trough.
• Wavelength ( λ - lambda): distance from one place in a wave
to the next similar. Ex: Distance from crest to crest.
• Frequency( ƒ ): the rate of repetition of a wave; measured
in hertz (Hz) = cycles per second. Ex: 3 cycles / second
• Cycle: one full wavelength represents one complete cycle
Draw the wave and label
•
•
•
•
•
Crest?
Trough?
Wavelength?
Amplitude?
Rest
Position?
Understanding the
Electromagnetic
Spectrum
Imagine bouncing a ball in a box… Describe and draw the
following if
• A ball is thrown hard
• A ball is thrown softy
1. Energy:
2. Frequency:
3.  :
Understanding the
Electromagnetic Spectrum
Which
wave has
more
energy?
Electromagnetic Waves From the Sun
1.
2.
3.
4.
5.
Which can we see?
 Infrared (heat)
Which can we feel?
 Visible Light (ROYGBIV)
Which is invisible to us?
 Ultraviolet (UV)
Which colours have the least energy? The most energy?
Which is dangerous?
Electromagnetic Waves From the Sun
• UVA and UVB rays can
penetrate
skin (short
Best ways to
avoid skinour
cancer:
energy)
1. Stay out ofwaves,
the sun/high
tanning
beds
2. Block UVA/UVB
3.• UVC
No smoking
rays are absorbed by
# way of getting
tanning
the wrinkles=
atmosphere
before they
reach the ground (waves
even shorter, higher
energy)
• Summer Months - UV is
highest
• Midday - UV highest at 10
AM and 4 PM
• Snow, Sand and Water -
Components of Visible Light
ROYGBIV
• Wavelengths of the light we can see is =10-6 m (400-700
billionths of a meter)
• “Visible light” is made up of ROYGBIV – colours of the
rainbow
• Visible white light is filled with colour!
Colours and Visible Light
• Visible light waves have different sizes
• The varying wavelength’s (’s) gives us ROYGBIV
• Which colours have the least energy? The most energy?
Penetrate human tissue
The Electromagnetic
Heat that we
but not bones.
feel!
Used for medical imaging,
Spectrum
Used in burglar
airport security and for
Carry information with
different combinations of
amplitude, frequency and
wavelength (AM radio,
FM radio)
TV, cell phones, satellites,
Electrobroadban internet, MRI
magnetic
scans
Radiation
alarms, motion
sensors, night
vision goggles.
photo’s of the insides of
pipes, engines and other
machines.
Use to heat food by
Produced by neutron
Has been used to
making water particles
stars and black holes in
disinfect drinking
in food vibrate.
galaxies.
water, waste
Radar – uses
Can penetrate tissues.
water, and in DNA
microwaves to measure
Used to sterilize medical
analysis.
speeds
equipment, to kill
RADARSAT – maps
cancerous cells.
Earth’s
surface
radar. are organized & classified in this
• All
forms
ofbyenergy
spectrum by their size of wavelength ~ width of the wave
Longest – Radio waves
Shortest – Gamma Rays
• Where is light in the spectrum?
Various Types of Light
Emissions
1) Luminescence
is light produced using energy
sources including or excluding
heat; can occur cooler
temperatures
a)
b)
Electrons of atoms become
excited & unstable when it
absorbs energy
The electron will return to
normal when it releases this
“extra” energy as light (photon).
2) Chemiluminescence
• Light energy released from a chemical reaction
without the involvement of heat or a flame (a cold
system)
• Ex: Glow-sticks, bioluminescence, luminol (a
chemical used in crime scenes – it glows when it
reacts with iron in blood.)
3) Bioluminescence
• Light is released by a chemical reaction;
occurs naturally in plants or animals.
• 90% of sea creatures are bioluminescent.
• Some fish produce their own light others have bacteria
do it.
• Deep sea creatures make their own light to
•
•
•
•
Find prey, attract predators (black sea dragon, angler fish)
Scare predators
Attract mates
Camouflage
• Fireflies – attract mates by flashing lights in specific patterns
• Others – Algae, crustaceans, earthworms, fungi
4) Incandescence
• Light energy produced by heated objects
substance becomes hot and glows
Ex: incandescence light bulbs – filament
inside that heats up when current flows
through it and emits light energy.
• Only 5% of energy is converted to light
• 95% is released as heat
5) Fluorescence
• A light emitted by substances
when they are exposed to EM radiation
Fluorescent light bulb
•
a glass bulb filled with gas (mercury vapour). The gas
particles get energized when electricity flows through.
• Inside of bulb is coated with white powder called a
phosphor
• Phosphor – glows when exposed to energized particles.
• 80% of energy is converted to heat, 20% to light
• Contains more toxins then incandescent bulbs
and require careful cleanup if broken
Other fluorescence – some rocks
6) Phosphorescence
• The ability to store energy from a light
source, and then emit it slowly over a long
period
of time. Ex: Glow in the Dark material
• The energy gets used up but can be reenergized by further exposure to a light
source.
Ex: Painted with phosphorescent ink
7) Triboluminescence
• Light produced by friction
• Eating lifesavers in the dark (crushing wintergreen
candy)
• Breaking apart sugar crystals
• Rubbing a diamond
8) Electric Discharge
• When an electric current passes through gases,
light is often produced
• Ex: Lightning, lamps
9) Light-Emitting Diode LED
• Electroluminescence – solid device that
transforms electric energy directly into
light energy
• LED’s
• Made out of a semi-conductor – material that
emits light when a small amount of current
passes through it.
• Use small amounts of electricity
• Last longer then other bulbs
• Light up much faster
• Used for, traffic lights, bilboards, x-mass lights,
handheld displays, brake lights
10) OLED, Plasma, Liquid Crystal
OLED – Organic light-emitting display
• Light source made of thin layers of organic molecules
that use electric current to produce light
• Use less energy, thinner, lighter, brighter, flexible
• Can be rolled, embedded into clothes
• Expensive to produce, can be damaged by water
Plasma Displays
• Each colour is a tiny fluorescent light, different phosphors
used to make red, green, blue light.
• Brighter images then LCD, more energy to operate
Liquid Crystal Displays - LCD
• A solid that can change the orientation of its molecules
like a liquid when electricity is applied
• Laptops, digital watches, cell-phones, iPods use LCD’s
Where does Light Come From?
• Comes from an energy source…
• Light can move through a
Vacuum, & through
different mediums
Which comes first,
lightning or thunder?
• How fast does light travel?
• Speed of Light = 299 792 458 m / s
• For simplicity, we will use:
Speed of light = 3.0 x 108 m/s
Sound is a wave too!
Speed of Sound= 340 m/s
Sound moves slower than light!
•
Light moves 300 000 000 meters every
second in a vacuum
How Does the Ball Behave?
How would
the ball
Imagine
behave…?
throwing
a
ball
through the
air…
Imagine throwing
a ball at a brick
wall…
Imagine
throwing a
ball under
water…
How does Light Behave?
The ball & light behave similarily:
• Light travels the fastest when…
There’s no matter…vacuum
• Light travels at differing speeds when…
It passes through matter…different mediums…
 REFRACTION (light bending)
• Light bounces back when…
It cannot penetrate a surface
REFLECTION (light scattering)
When light hits an object, it can be…
1. Transmitted- pass through the object
Rays – represent light as a
straight line
2. Refracted- light bends as it is absorbed by the object
3. Reflected- light is scattered away from the object
Material classification
by how they transmit light
Transparent
•Transmit light freely
•Can see through it clearly
Translucent
•Transmit some light
• but not enough to see through clearly
Opaque
•Absorb and reflect light but do not transmit it
Law of Reflection
• Reflection from a plane mirror:
Normal
Incident ray
Angle of
incidence (θ i)
Angle of
reflection (θ r)
Reflected ray
Mirror
Mirror
“Normal line”
is perpendicular
(90) to the surface
The Law of Reflection
Angle of incidence (θ i ) = Angle of reflection (θ r )
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The same !!!
Greek letter, theta (θ).
Common symbol for
angle. Angle (θ) is
measured FROM
the NORMAL to the ray
Ray Diagrams
• Ray Model of Light
 Allows us to trace the
path that light travels
• Why? So we can predict the
location of the reflected
image of an object
• Note: The rays (incident ray
and the reflected ray) are
drawn as straight arrows
Clear vs. Diffuse Reflection
• Smooth, shiny
surfaces have a clear
or regular reflection.
Rough, uneven surfaces
have a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
Seeing Reflected ImagesRay Diagrams
“Plane mirrors produce
upright virtual images
with lateral inversion”
1. Draw a solid line
perpendicular from the
object to the mirror.
2. Extend the line (dashed)
an equal distance
behind the mirror
Seeing Reflected ImagesRay Diagrams
“Plane mirrors produce
upright virtual images
with lateral inversion”
Why virtual?
1. Draw a solid line
perpendicular from the
object to the mirror.
2. Extend the line (dashed)
an equal distance
behind the mirror
Seeing Reflected ImagesRay Diagrams
“Plane mirrors produce
upright virtual images
with lateral inversion”
3. Draw a normal halfway
between the object and eye.
Seeing Reflected ImagesRay Diagrams
“Plane mirrors produce
upright virtual images
with lateral inversion”
4. Draw solid rays from the
object, reflecting on the
mirror and to the eye.
θi= θr
Seeing Reflected ImagesRay Diagrams
“Plane mirrors produce
upright virtual images
with lateral inversion”
5. Extend the reflected line
(dashed) backwards
behind the mirror until it
hits the other line.
6. Repeat for all other
distinctive parts of the
object.
Seeing Reflected ImagesRay Diagrams
Now YOU try!
Image Characteristics
S (size)- same, smaller,
or larger
A (attitude)- same,
right side up
Inverted (upsided down)
L (location)- same, above,
or below
T (type)- real or virtual
Using mirrors
• Two examples:
2) A car headlight
1) A periscope
Ray Diagrams Continued….
What if the
1. Concave Mirrors (converging)
- collects light rays & brings them to
a single point.
- Produces larger images
2) Convex Mirrors (diverging)
- designed to spread light rays out
- Produce smaller images
Which is Concave? Convex?
mirror is
curved?
Applications to
Concave Mirrors
Concave Mirrors
- used in flashlights, telescopes,
cosmetic mirrors, headlights of
a car, dentist lights
- concentrates light to one
particular spot.
Applications for Convex
Mirrors
Convex Mirrors:
- used in security mirrors at
variety stores, side-view and
rear view mirrors in a car
- Allows you to view a larger
region from one location
Terminology for Curved Mirrors
We will first use a Concave Mirror to label these terms..
• Vertex – midpoint of the curved mirror
• Principal Axis – a straight line that passes through the
vertex (symmetrical & perpendicular)
• Center of Curvature (C) – think of it as the center of a
circle; it lies on the principal axis
• Radius of Curvature (R) – distance from the vertex to
the center of curvature
Terminology for Curved
Mirrors
 From the focal point
to the vertex has a
length of… f .
 What is the length
from C to the vertex?
• Focus or Focal Point (F ) – the half way point from
the center of curvature (C ) to the vertex; this is
where reflected rays* pass through and converge
*Reflected rays pass the focal point when incident
rays are parallel to the principal axis
• Focal length (f ) – the distance from the vertex to
the focus or focal point (F )
Diagram for Curved Mirrors
• We applied the new terminology for a Concave Mirror.
• Now, YOU try labelling the terms for a Convex Mirror!
Which way is convex?!
• Remember :
* Principal Axis (PA)
* Vertex
* Center of Curvature (C)
* Radius of Curvature (R)
* Focus or Focal Point (F)
* Focal Length (f )
Ray Diagrams for Concave Mirrors
Depending on where the object is located on the
principal axis, ray diagrams are used to determine…
S A L T
• S = the SIZE of the Reflected Image (smaller, larger,
or the same as the object)
• A = the ATTITUDE of the RI (right-side up or upside
down
• L = the LOCATION of the reflected image (RI)
• T = the TYPE (real or virtual)
We will look at 5 cases…
Drawing Ray Diagrams
for Concaved Mirrors
•
1st incident ray is drawn parallel to the principal axis, starting
from the top of the object to the mirror (blue).
•
Can you predict and draw the reflected ray (red)?
•
2nd incident ray is drawn from the top of the object through
the focal point to the mirror (blue)
•
Predict and draw the reflected ray (red).
•
The image is formed where the rays intersect. This
intersection point on the image is the same point that was on
the object.
Image
Characteristics
1. Object
is Located
S-
Center of Curvature
Beyond the
Any Incident
Rays Rays
Any Incident
• 1st incident
ray parallel
is drawn
parallel
travelling
to
thetheto
passing
through
the principal
axis,
starting
from
principal
axis
will
reflect
FOCAL
POINT
will the
•A- top ofand
the pass
object
to the
through
the (blue).
reflect
andmirror
travel
focal
point
parallel
thethe
principal
• Can you
predict
and to
draw
reflected rayaxis
(red)?
•
2nd incident ray is drawn from the
•L- top of the object through the focal
point to the mirror (blue)
• Predict and draw the reflected ray
(red).
General Conclusion
••T- The image is formed where the rays
An object located beyond the Center
intersect. This intersection point on
of Curvature will reflect an image that is:
the image is the same point that
was on the object.
• located between C and F
• Is real, smaller and upside down
2. Object is Located at the
Center
of Curvature
Image Characteristics
SSame as previous slide…
• 1st incident ray travels parallel to
Aprincipal axis from the top of object
towards the mirror (blue)
• Predict & Draw reflected ray (red)
• 2nd incident ray travels from the top
L-of the object through the focal point General Conclusion
An object located at the Center of
to the mirror (blue)
Curvature
will reflect an image that is:
• Predict & Draw reflected ray
(red).
• The imageWhat
is formed
where the rays
do you
T-intersect.
• Also located at C
notice about
the image? • Is real, same size and upside down
3. Object
is Located
Image
Characteristics
Between
the Center of Curvature and
Focal Point
S-
Same as previous slide…
• 1st incident ray travels parallel to
A- principal axis from the top of object
towards the mirror (blue)
• Predict & Draw reflected ray (red)
• 2nd incident ray travels from the top of
to
L- the object through the focal point General
Conclusion
the mirror (blue)
Anray
object
• Predict & Draw reflected
(red). located between the Center
of Curvature
• The image is formed where
the rays and the Focal Point will
reflect an image that is:
intersect.
T-
• located beyond C
Is real, larger size and upside down
Image
Characteristics
4. Object
is Located
S-
Between
the Focal Point and Mirror
Same as previous slides…
• The 1st ray is drawn parallel to
A- the principal axis from the top of
the object to the mirror (red)
• Can you predict and draw the
reflected ray?
• The 2nd ray is drawn from the top
of the object through the focal
L- point to the mirror (blue)
General Conclusion
• Predict and draw the reflected
ray.
An object that is located between the
• The image is formed where the
Focal
point and the mirror will reflect
rays intersect. This point
on the
Timage is the same point that was an image that is:
on the object
• located behind the mirror
• Is right side up, larger and is virtual
5. Image Is Located at the
Focal Point
• 1st incident ray travels
parallel to principal axis from
the top of object towards the
mirror (blue)
• Predict & Draw reflected ray
(red)
• 2nd incident ray travels from
the top of the object through
the focal point to the mirror
(blue)
• Predict & Draw reflected ray
(red).
• What do you notice…?
No SALT
Ray Diagrams for Convex
Mirrors
What does a Convex Mirror look like again ?
- Surface curving outwards
Unlike the concave mirror with 5 different cases, the convex mirror has
only one case. SALT is still used to determine the image’s
characteristics:
The object’s distance to
the mirror doesn’t change
the image’s SALT
S- image is smaller than the object
A- image is in the upright position
L- image is located behind the convex mirror
T- virtual image
Calculations for Curved Mirrors & Thin Lenses
To calculate object or image dimensions mathematically we use:
Thin Lens Equation (Gaussian Lens Formula)
1
1 1


f do di
m
Magnification Equation
-Measure of how much
Larger or smaller the object
hi
d
 i
ho
do
M>1 or < -1 ()
1 > M > -1 ()
hi
di
m

ho
do
Ex 1: Find the image position and magnification
for a convex mirror with a focal length 20cm,
with a candle 5.0cm away from the vertex.
Ex 2: A diverging lens of focal length 200cm is
used to correct a person’s nearsightedness. Find
the image position of an object 3.00m away.
What type of mirrors?
Negatives: (same for mirrors and lenses)
Focal point
-f
-‘ve diverging
mirror/lens
Magnification -m
-‘ve inverted
image
Image Distance -di
-‘ve virtual image
(in front of lens of behind mirror)
Light Refraction
•
What happens when light rays do
NOT reflect?
•
In a vacuum, light travels in a
straight line …
However, if light rays encounter a
medium (matter), such as water,
then what happens?….
•
•
•
Light bends as it passes through
water!
The straight-line path of light
CHANGES!
Light Refraction
• LR are light rays bending when it passes through
different mediums (light changes its speed,
either slowing down or speeding up
Ex: light passes from air to water & vice versa
• The more the light ray slows down, the more the
light is refracted (bends more).
• Light only refracts at the boundary of the two
different mediums
Index of Refraction
• I of R is a number, a value given to a medium…
- The amount by which a medium decreases the
speed of light is indicated by this value I of R
• The larger the I of R for that medium,
the more it decreases the speed of light.
Ex: Diamonds slow down (bend) light more than
water, thus diamonds have a greater index of
refraction than water
• Certain materials bend light in similar
ways…thus they have similar indexes of
refraction
Refracted Index
• Light travelling in a vacuum – Refracted Index is 1.00
• Light travelling in air – RI is 1.0003 ~ 1.00
• Light travelling in water – RI is 1.33
c  3.0 108 m / s
How are these values obtained?
- Index of Refraction of Material is found by comparing
speeds of light in their respective mediums
Refracted Index (n ) = speed of light in vacuum (c )
speed of light in medium (v )
c
n
v
RI and θ of Refraction
Snell’s Law
• Angle of Refraction: amount of light bending
• Snell’s Law: When light travels from air (low
RI) into water (higher RI), it bends TOWARDS
the normal,
θi > θr
• (speed )
  RI =
 θ Refraction
(closer to normal)
• When light travels from water (denser, higher
RI) into air (less dense, lower RI), refracted
ray bends AWAY from the normal (speed )
- The more the medium slows down the light, the
greater the difference between θ i and θ r
Total Internal Reflection
(TIR) = Trapped Light
• LR is light bending when traveling through
different mediums…
• As the angle of θi increases to the normal, θr
increases too.
• At a certain angle  critical angle ( θc ),
refracted rays will not leave the
medium; instead travel along the
boundary line.
• Increase θi even more & the ray will no
longer refract, but only reflect rays.
(trapped within the medium)
• TIR – when θi > θc, light rays no longer
refract, but reflect and stays within the
medium
Dispersion
•
•
•
Special type of refraction in
diamonds, rain drops, and prisms
They can be colorless or show all
the colours of the
rainbow…dispersion is when the
refraction of white light is
separated into its colours
Each colour travels a slightly
different speed when it goes
through the glass prism. Violet
light slows down more then red.
Ex. Rainbow: light passes
through rain drops and
some light is reflected BUT
some light is refracted as
well
Light is refracted twice, when
light enters and when light
leaves….both separate light
into its colours
The Physics of Bling
1. The index of refraction
of a diamond is 2.4
• One of the highest for a
clear substance
• Explains why diamonds
are bling
2. The angle of incidence
of diamonds should be
24.5…making it glitter
Optical Illusions:
Both Reflection and/or Refraction
1. Desert Mirages
•
•
•
An image of a distant object
produced as light refracts through
air of different densities
Light is internally reflected and
refracted as it passes through the
progressively hot air lying near the
ground, light is totally internally
reflected
There appears to be a lake in the
distance, but this is actually the
image of the sky produced by light
bending near the hot air near the
ground…
2. End of the Rainbow
•
Location of rainbows are relative to
YOU, the SUN, and the RAIN
Optical Illusions:
Both Reflection and/or Refraction
3. Shimmering
•
•
•
•
•
The shimmering image of the moon on a lake at
night.
Light is refracted when passing through air of
different temperatures.
Air above the lake is much warmer. Light
travels through cooler air slowly and bends
toward normal.
Continues through warmer layer bending further
from the normal.
Eventually TIR occurs and multiple virtual
images of the moon on the lake result.
4. Apparent Depth
•
•
The depth that an object appears to be due to
the refraction of light in a transparent medium.
The object under water always appears to be
nearer to the surface then it actually is.
Optical Illusions:
Both Reflection and/or Refraction
5. The “Flattened” Sun
• Sun appears flattened
during sunrise and
sunset?
• This is due to the
common phenomenon
of atmospheric
refraction.
Applications of TIR
• Fiber Optics:
Light travels in a straight line, BUT what if
you want light to bend?
Optical fibre: thin transparent glass tube that
transmit light around corners…the light
does not escape because of TIR
Fiber Optics are used to transmit telephone
and internet communications
A optical fibre cable is made of 1000’s of
optical fibres packed together
Lenses
Types of Lenses
There are two types of lenses:
1. Converging (Convex)
1. Diverging (Concave)
Converging Lenses
• …have a positive focal length (f>0)
• Cause rays to intersect at the focal point
• Used for magnifying glasses, microscopes,
telescopes and reading glasses… REAL IMAGE
(if on the same side as the viewer)…3 out of 5
Diverging Lenses
•…have a negative focal length (f<0)
•Cause rays to spread out as if they came from a
focal point…IMAGE is on same side as object…
VIRTUAL IMAGE (always)
•Used for distance glasses.
Lens Terminology
Optical Centre,
O
Focal length, f
Principal Axis
2F’
Focal point, F’
F’= secondary focus
F’ is on the opposite side
for diverging lenses
Focal point, F
2F
Ray Rules–
Converging Lens
If the incident
ray…
then the refracted
ray…
is parallel to the
principal axis,
Goes through F
comes through the Emerges
focus,
parallel to the
principal axis
comes through the Is not refracted.
optical centre,
Diagram
Forming an Image
• Draw a ray from the object to
the lens (use one of the special
rays described).
• From the same position on the
object, draw another special
ray.
• The image is located where the
refracted rays meet.
Converging Lens- 5 Cases
1. Beyond 2F’
2. Object at 2F’
Converging Lens- 5 Cases
3. Between 2F’ and F’
4. At F’
Converging Lens- 5 Cases
Between F’ and O
Example
• Find the image for the following
case:
Five Case Scenarios for
Converging Lenses
Object
Position
Location
Image
Attitude
Size
Type
Beyond 2f’
Between f
and 2f
inverted
smaller
real
At 2f’
At 2f
inverted
same size
real
Between f’
and 2f’
Beyond 2f
inverted
larger
real
At F’
Between F’ Behind
object
and O
No Image Formed
upright
larger
virtual
Ray Rules–
Diverging Lens
If the incident
ray…
then the refracted
ray…
is parallel to the
principal axis,
Emerges as if it
came from F.
Is aimed at the
focal point prime,
Emerges
parallel to the
principal axis
comes through the
optical centre,
Is not refracted.
Diagram
One Case Scenario for
Diverging Lenses
• With a diverging lens, the image
is always:
•
•
•
•
Between F and O
Upright
Smaller
Virtual
The Eye
• What is the function of?
• Cornea
• Aqueous and vitreous
humour
• Lens
• Ciliary muscle
• Retina
• Choroid
What parts of
• Sclera
the eye are
• Optic nerve
directly
• blind spot
related to the
• Fovea
unit?
• Iris
Vision Conditions
Normal Vision: focus point is at the
back of the retina
Myopia (near-sightedness): distant
objects are blurry, 1/3 of people,
longer eye ball
Hyperopia (far- sightedness) close
objects are blurry, shorter eye ball
or flat cornea
Eye
ConditionsS
ummary
Vision Conditions
Presbyopia: loss
of flexibility of
eye’s natural
lens ~40 years,
need bifocals or
reading glasses
Astigmatism: eye
has 2 focal
points instead of
1
Application of Optics
Telescopes
Amateur astronomers use
reflecting and refracting
telescopes
• A reflecting telescope
uses mirrors to focus light
from a distant
object…how?
• A refracting telescope
uses a lens…how?
How does “focusing” work?
Unit Review
• Go back over all
worksheets
• Practice ray diagrams
for Plane and curved
mirrors, and lenses
• Practice magnification
problems for mirrors
and lenses
• Make unit study notes