Transcript Eletromagnetic waves Notes

Light and Optics
Section 1: Intro to Electromagnetic Waves
• Intro Questions:
1. What is the difference between mechanical
and electromagnetic waves?
2. Name as many types of electromagnetic
waves you can
3. What is the speed of light and any other
electromagnetic wave in space?
The Electromagnetic Wave
Electric Field
• Characteristics:
– Require no medium
– Transverse waves of oscillating electromagnetic fields
– Transverse waves move perpendicular to the direction
the wave moves
– The electric and magnetic fields are at right angles to
each other
– All electromagnetic waves travel at 3.0 x 108 m/s
Magnetic Field
Direction
of travel
towards
you
The Electromagnetic Spectrum
Wavelength Decreases
Frequency Increases
Energy Increases
108
Velocity = 3.0 x
m/s
For All Electromagnetic Waves
3.0 x
8
10V
=λ•f
More Penetration and
Dangerous
Activity 1
1. Label all the parts of the electromagnetic spectrum
in order of increasing frequency.
2. Radio Waves, Microwaves, Infrared, Visible Light,
Ultra Violet, X-rays, Gamma Rays
3. Label the trend lines as well
Activity 1
1.
2.
3.
Label all the parts of the electromagnetic spectrum in order of increasing
frequency.
Radio Waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays,
Gamma Rays
Label the trend lines as well 4 Visible Light
1 Radio
waves
2
Microwaves
3 Infrared
5 Ultra Violet
6 X-Rays
7 Gamma
Rays
Wavelength Decreases
Frequency Increases
Energy Increases
More Penetration and Dangerous
Section 2: Electromagnetic Wave Math
V=λ•f
Speed of light distancetime calculations
• Velocity = 3.0 x 108 m/s for all electromagnetic
waves
• If you see any of these you have an
electromagnetic wave and v = 3.0 x 108 m/s
• Radio Waves, Microwaves, Infrared, Visible
Light, Ultra Violet, X-rays, Gamma Rays
Example 1
The AM radio band extends from 5.4 x 105 Hz to
1.7 x 106 Hz. What are the longest and shortest
wavelengths in this frequency range?
Example 1
The AM radio band extends from 5.4 x 105 Hz to
1.7 x 106 Hz. What are the longest and shortest
wavelengths in this frequency range?
Example 2
What is the frequency of an electromagnetic
wave if it has a wavelength of 1.0 km?
Example 2
What is the frequency of an electromagnetic
wave if it has a wavelength of 1.0 km?
Example 3
How long does it take for light from the sun to
reach Earth if the sun is 1.5 x 1011 m away?
Example 3
How long does it take for light from the sun to
reach Earth if the sun is 1.5 x 1011 m away?
Intro
1. What are the primary colors of light?
2. List the colors of the rainbow in order
3. What do all the colors of the rainbow add up
to?
Section 3: Visible Light and Colors
Visible Light
• Characteristics
– “White” light is a combination of red, orange,
yellow, green, cyan, blue, and violet
– A prism can separate these colors out
• By refraction of different wavelengths of color
Visible Light
700 nm
400 nm
Red orange yellow green cyan blue violet
Red:
• Longest
Wavelength
• Lowest
Frequency
• Least Energy
Violet:
• Shortest
Wavelength
• Highest
Frequency
• Most Energy
Activity 2
• List the colors of the rainbow in order
from lowest to highest frequency
• Color this at home
Lowest
Frequency
Highest
Frequency
________ ________ ________ ________ ________ ________ ________
Activity 2
• List the colors of the rainbow in order
from lowest to highest frequency
• Color this at home
Lowest
Frequency
Red orange yellow green cyan blue violet
Highest
Frequency
• Primary Colors
– Red
– Blue
– Green
Blue
Red
Green
• Secondary Colors: Mixture of 2 Primary Colors
– Magenta (Blue and Red)
Blue
Magenta
Red
– Cyan (Blue and Green)
Blue
Blue
Cyan
Green
– Yellow (Red and Green)
Blue
Red
White
Red
Yellow
Green
Green
• A mixture of all three primary colors produces white light
• Primary Colors
– Red
– Blue
– Green
Blue
Red
Green
• Since secondary colors are a mix of two
primaries:
• Mixing primary and secondary colors produces
white light
Blue
White Light
= Primary Color + Secondary Color
Green
• White Light Red= Blue + Yellow
• White Light
= Green + Magenta
• White Light
= Red + Cyan
Activity 3
• Color and label the color mixture diagram
White Light = Primary Color + Secondary Color
White Light= ___________+ ____________
White Light= ___________+ ____________
White Light= ___________+ ____________
Activity 3
• Color and label the color mixture diagram
White Light = Primary Color + Secondary Color
White Light
= Blue + Yellow
White Light
= Green + Magenta
White Light
= Red + Cyan
White
Primary colors of light
Red
Blue
Green
Primary pigments (ink)
Magenta
Cyan
Yellow
• Primary colors (light) are secondary pigments
– Red
– Blue
– Green
Red
Magenta
Yellow
Green
Blue
Cyan
• Primary pigments (ink) are secondary colors
– Magenta
– Yellow
– Cyan
Yellow
Green
Red
Cyan
Blue
Magenta
Intro
• Do section 3 of your worksheets as your intro
today
Section 4: Refraction of Light
• Optics is the science that describes the
behavior and properties of light and the
interaction of light with matter.
• Refraction- Bending of light as it
travels from one medium to
another.
• Refraction occurs because lights
velocity changes in another
medium.
• Light does not need a medium but
it is affected by it.
Key items for refraction
• Light travels from the object to the observers
eyes
• Light travels at different speed indifferent
medium
Normal Line
• Terms to know:
– Normal line
– Angle of incidence Θi
– Angle of refraction Θr
Θr
Slower Medium
Θi
• As light moves into a new medium, part of it is
reflected and part is refracted
(a) Into slower medium light
bends toward the normal line
(b) Into faster medium light
bends away from the normal
line
• Objects appear to be in a different position
due to refraction
– An object “appears” to be straight ahead
– Light always travels from the object to the
observers eyes, bending into the new medium
Cats Perspective
Fishes Perspective
• Index of refraction (n)- the ratio of speed of
light in a vacuum to speed of light in that
substance.
– Always greater than 1 because light in a vacuum is
the fastest
(n = 1.00 for a vacuum)
– Has no unit
n = index of refraction
c = speed of light in a vacuum
v = speed of light in medium
Example 4
• Tom, a watchmaker, is interested in an old
timepiece that’s been brought in for a
cleaning. If light travels at 1.90 x 108 m/s in
the crystal, what is the crystal’s index of
refraction?
Example 4
• Tom, a watchmaker, is interested in an old timepiece that’s been brought
in for a cleaning. If light travels at 1.90 x 108 m/s in the crystal, what is the
crystal’s index of refraction?
Example 5
• How fast does light travel in fluorite
(n=1.434)?
Example 5
• How fast does light travel in fluorite
(n=1.434)?
• Snell's Law- a formula that describes the angle
of incidence and angle of refraction
(ni)(sin Θi) = (nr)(sin Θr)
ni = index of refraction of first medium (incidence side)
Θi = angle of incidence
nr = index of refraction of second medium (refracted side)
Θr = angle of refraction
(ni)(sin Θi) = (nr)(sin Θr)
Can be rearranged
to solve for ni
Can be rearranged
to solve for nr
(ni)(sin Θi) = (nr)(sin Θr)
Can be rearranged
to solve for Θi
Can be rearranged
to solve for Θr
Example 6
A light ray traveling through air (n=1.00) strikes a
smooth, flat slab of crown glass (n=1.52) at an
angle of 30.0° to the normal.
a. Find the angle of refraction
b. Draw a picture and label it
Example 6
• A light ray traveling through air (n=1.00) strikes a
smooth, flat slab of crown glass (n=1.52) at an angle of
30.0° to the normal. Find the angle of refraction.
Example 7
Find the angle of refraction for a ray of light that
enters a calm lake at an angle of 25° to the
normal. (nair = 1.00 and nwater = 1.33)
Example 7
Find the angle of refraction for a ray of light that
enters a calm lake at an angle of 25° to the
normal. (nair = 1.00 and nwater = 1.33)
Section 5: Critical Angle
• What happens when you increase the angle of
incidence when going from a slow to a fast medium?
• Remember: slow to fast bends away from the normal
• What happens if you increase the angle of incidence
beyond here?
• Total internal reflection
Θr
nr = 1.00 (faster)
ni = 1.33 (slower)
Θi
Click on the picture for a critical angle animation
• Critical angle- Angle at which there would be
no refraction; only total internal reflection.
• Critical angle equation (θc = critical angle)
Θr
nr = 1.00 (faster)
ni = 1.33 (slower)
Θi
Example 8
• A jeweler must decide whether the stone in Mrs.
Harder’s ring is a real diamond or a less-precious
zircon. He measures the critical angle of the gem and
finds that it is 31.3°. Is the stone really a diamond or
just a good imitation? (ndiamond = 2.41, nzircon = 1.92, nair
= 1.00 )
nair always the smaller n in
critical angle problems
n in question: solve for this
Example 8
• A jeweler must decide whether the stone in Mrs.
Harder’s ring is a real diamond or a less-precious
zircon. He measures the critical angle of the gem and
finds that it is 31.3°. Is the stone really a diamond or
just a good imitation? (ndiamond = 2.41, nzircon = 1.92, nair
= 1.00 )
Intro
Work on section 5 and 6 of your worksheets
Intro
• Study for your quiz a few minutes
• Borrow a ruler if you do not have one today
and tomorrow. Return them before the quiz
• The quiz will take place after our lesson today
Section 6: Reflection and Intro to Mirrors
• Why can you see a reflection on the surface of
one object but not on the surface of another?
• It depends on how smooth the surface is
Reflections
• Planar reflection -off of a smooth surface
Planar reflection
• Diffuse reflection - reflection off of a rough of
textured surface.
Diffuse reflection
Plane Mirrors
• A plane mirror is a flat mirror
• Plane mirrors produce
images that are:
– Virtual - image that appears
behind the plane of the mirror.
– Upright – Up in the mirror is
the same as the object
– Non-magnified – Appear the
same size as if the object was
that distance away
– Reversed
Concave (Converging) mirror
Produce two types of images depending on where
the object is located relative to the focal point
• Real inverted images (object beyond focal point)
• Magnified virtual upright images (object between focal
point and surface of mirror)
Concave (converging) mirror
Why two names?
– Concave: name because of shape
– Converging: name because of what light does
• bends inward or converges
Bends inward toward the object
Convex (diverging) mirror
• Only produce virtual, upright, and smaller
images
Convex (diverging) mirror
Why two names?
– Convex: name because of shape
– Diverging: name because of what light does
• bends outward or diverges
Bends outward away from the object
• What kind of mirror would water act like?
• Why? (What kind of image is formed here)
• What kind of mirror would this be like?
• Why? (What kind of image is formed here)
• What kind of mirror would this be like?
• Why? (What kind of image is formed here)
Section 7: Planar Ray Diagram
A Ray Diagram
• A drawing allows you to determine the size and
orientation of an image formed with a mirror or lens.
• The real side of the mirror is the side the object is on
Mirror
The real side of a mirror
The virtual side of a mirror
Activity 4: Drawing a Ray Diagram in a planar mirror
1. First draw the object, the mirror plane, label p
and h. (the object is traditionally drawn as an
arrow)
• do is the distance to the mirror from the object
• ho is the height of the object
do
ho
Object
Drawing the Rays
1. Draw a ray perpendicular to the mirrors surface and include its
reflection
2. Draw a single ray going at an angle away from the object to the
mirror (Include its reflection)
3. Since the rays don’t cross on the real side of the mirror, after
the reflection, extend them until they meet on the virtual side.
4. This is where the image would appear, draw the image, with
the top being where the rays intersect
5. Then finish the labeling
1
ho
Object
di
do
2
3
4
hi
Variables you need to know
•
•
•
•
do is the distance to the mirror from the object
di is the distance from the mirror to the image of the mirror
ho is the height of the object
hi is the height of the image
do
di
hi
ho
Object
Image
Now we can analyze the image
The image formed in a planar mirror is
1. Virtual
2. Same size
3. Upright
ho and hi are equal
Virtual: on this
side of a mirror
1
ho
Object
di
do
2
3
4
hi
Facing up
Example 9
• Law of Reflection Review
• Mary sees a reflection of her cat sparkles in the
living room window. The image of Sparkles
makes an angle of 40° with the normal, at what
angle does Mary see Sparkles reflected?
Θr = ?
Θi = 40°
Example 9
• Law of Reflection Review
• Mary sees a reflection of her cat sparkles in the
living room window. The image of Sparkles
makes an angle of 40° with the normal, at what
angle does Mary see Sparkles reflected?
Θr = 40°
Θi = 40°
At 40° to the normal line
Intro
a. __________________ What is line C called above?
b. __________________ What would be the angle or reflection
be in the diagram above?
c. __________________ What would be the angle of refraction
be in the diagram above?
d. __________________ What would be the critical angle above
be for the light beam in a substance(n=1.59) shown above?
Intro
a. __________________ What is line C called above?
b. __________________ What would be the angle or reflection be in the
diagram above?
c. __________________ What would be the angle of refraction be in the
diagram above?
d. __________________ What would be the critical angle above be for the
light beam in the substance (n=1.59) shown above?
Section 8: Concave Mirror Ray Diagram
Curved Mirror Ray Diagram
• More variables you need to know for a curved
mirror
– Center of curvature (C) – the center of the curve if
it was a sphere
– Focal Point (F) – ½ from the mirror to the center
of curvature
– Principal axis- the line that the base of the arrow
is on.
Principal axis
C
F
Rules for Drawing Reference Rays (Concave Mirror)
Ray Line drawn from object to
mirror
1. Parallel to principal axis
Line drawn from mirror to
image after reflection
Through focal point F
2.
Parallel to principal axis
Through focal point F
C
F
The image appears
where all rays intersect
Activity 5
• Now analyze the image just formed
• Its:
– Smaller
– Inverted
– Real
(hi is less than ho)
(upside down)
(on the object side of a mirror)
object
ho
image
Activity 5
hi
• A convex mirror produces many different
types of images
• Click picture for concave mirror animation
Rules for Drawing Reference Rays (Concave Mirror)
Ray
Line drawn from object to mirror
Line drawn from mirror to image after reflection
1.
Parallel to principal axis
Through focal point F
2.
Through focal point F
Parallel to principal axis
C
F
The image appears
where all rays intersect
Activity 5
• Now analyze the image just formed
• Its:
– Not magnified (ho = hi)
– Inverted
(upside down)
– Real
(on the object side of a mirror)
object
ho
C
F
image
Activity 5
Rules for Drawing Reference Rays (Concave Mirror)
Ray
Line drawn from object to mirror
Line drawn from mirror to image after reflection
1.
Parallel to principal axis
Through focal point F
2.
Through focal point F
Parallel to principal axis
C
F
The image appears
where all rays intersect
Activity 5
• Now analyze the image just formed
• Its:
– magnified (ho < hi)
– Inverted
(upside down)
– Real
(on the object side of a mirror)
object
ho
C
F
hi
image
Activity 5
Rules for Drawing Reference Rays (Concave Mirror)
Ray
Line drawn from object to mirror
Line drawn from mirror to image after reflection
1.
Parallel to principal axis
Through focal point F
2.
Through focal point F
Parallel to principal axis
C
F
Activity 5
• Now analyze the image just formed
• Its:
– No image formed
– Does not intersect on the real or virtual side
C
F
Activity 5
Rules for Drawing Reference Rays (Concave Mirror)
Ray
Line drawn from object to mirror
Line drawn from mirror to image after reflection
1.
Parallel to principal axis
Through focal point F
2.
Through focal point F
Parallel to principal axis
C
F
Activity 5
• Now analyze the image just formed
• Its:
– magnified (ho < hi)
– upright
– Virtual
(on the virtual side of a mirror)
image
object
C
ho
hi
F
Activity 5
Section 9: Convex Mirror Ray Diagram
Rules for Drawing Reference Rays (convex mirror)
Ray Line drawn from object to
mirror
1. Parallel to principal axis
Line drawn from mirror to
image after reflection
2.
Through focal point F
Parallel to principal axis
3.
Follow the arrow tips away from the mirror back with virtual
lines until they intersect
Through focal point F (away from the mirror)
F
Activity 6
C
This is where the
image appeared
• Now analyze the image just formed
• Its:
– Smaller
(hi is less than ho)
– Upright
– Virtual
(on the other side of a mirror)
– A convex mirror always produces this type of
image
This is where the
image appeared
Intro
• Do the following ray diagrams:
• 1.
• 2.
F
C
F
C
3. List the objects that are
Plane Mirrors
Concave Mirror
Convex Mirrors
Section 10: Mirror Math
Lens/ Mirror Math Cheat Sheet
Take out a piece of paper and copy all of this
Mirror Math Equations
If M is negative then the image is
inverted
• The object side is always positive for lenses
and mirror math
• The image sign depends on image location
• The image here would have a positive value
• The image here would have a negative value
do
di
Positive object side
Positive image side of mirror
Positive focal side of mirror
di
• The focus is on the side of the center of
curvature
• The concave mirror always curves to the real
side and has a positive F
F
Positive focal side of mirror
• The focus is on the side of the center of
curvature
• The convex mirror always curves to the virtual
side and has a negative F
F
Positive focal side of mirror
Example 10
A concave mirror has a focal length of 10.0 cm.
Locate the image of a pencil that is placed
upright 30.0 cm from the mirror.
a. Find the magnification of the image.
b. Draw a ray diagram of the situation
C
F
Example 10
• A concave mirror has a focal length of 10.0
cm. Locate the image of a pencil that is placed
upright 30.0 cm from the mirror.
a. Find the magnification of the image.
Example 10
A concave mirror has a focal length of 10.0 cm.
Locate the image of a pencil that is placed
upright 30.0 cm from the mirror.
b. Draw a ray diagram of the situation
C
F
Example 11
Mark is polishing his crystal ball. He sees his
reflection as he gazes into the ball from a
distance of 15 cm.
a. what is the focal length of Mark’s crystal ball
if he sees her reflection 4.0 cm behind the
surface?
b. Is the image real or virtual
Example 11
Mark is polishing his crystal ball. He sees his reflection as he gazes into the ball from a
distance of 15 cm.
a. what is the focal length of Mark’s crystal ball if he sees her reflection 4.0 cm
behind the surface?
b. Is the image real or virtual
Example 12
You look into an empty water bowl from 6.0 cm
away and see a reflection 12 cm behind the
bowl.
a. What is the focal length of the bowl?
b. What is the magnification of the image?
Example 12
• You look into an empty water bowl from 6.0 cm away and see a reflection
12.0 cm behind the bowl.
a. What is the focal length of the bowl
b. What is the magnification of the image?
Intro:
1. Mark looks into a concave mirror from 5 cm
away. If the image appears 10 cm behind
the mirror:
a) What is the magnification?
b) What is the focal length?
Section 11: Intro to Lenses
The Lens Movie Clip
Types of lenses
• Convex (converging) lens
• Concave (diverging) lens
Name for what light does is opposite of mirrors
Convex (converging) Lens
Why two names?
– Convex: name because of shape
– converging: name because of what light does
• bends inward or converges
Near side bends outward away from the object
Concave (diverging) Lens
Why two names?
– Concave: name because of shape
– Diverging: name because of what light does
• bends outward or diverges
Near side bends inward toward the object
•
•
•
•
•
•
•
•
The Lens
do – distance to object
di – distance to image
ho – height of object
hi – height of image
F’ – virtual focal point
2F’ – double virtual focal point
F – focal point
2F – double focal point
do
ho
di
Object
2F’
2F
F’
Virtual side in lenses
F
Image
Real side in lenses
hi
Section 12: Concave Lens Ray Diagram
Rules for Drawing Reference Rays (concave/diverging lens)
Ray Line drawn from object to lens Line drawn from mirror to
image after refraction
1.
Parallel to principal axis
Through focal point F’
2.
Through center of lens
Continue straight
3.
Follow the arrow tips back to the virtual side where they
intersect
Activity 7
2F’
F’
The image appears
where all rays intersect
F
2F
Concave/diverging lens
• Always produces a:
– Virtual
– Upright
– Smaller image
Section 13: Convex Lens Ray Diagram
Rules for Drawing Reference Rays (convex/converging lens)
Ray Line drawn from object to lens Line drawn from mirror to
image after refraction
1.
Parallel to principal axis
Through focal point F
2.
Through center of lens
Continue straight
3.
Place the image head where the rays intersect or trace the rays
to the virtual side if they don’t intersect
2F
2F’
Activity 8
F’
F
• Image produced:
– Outside focal point (F’):
•
•
•
•
Convex/converging
lens
Real and inverted
Outside 2F’: smaller
At 2F’: same size
Between 2F’ and F’: magnified
– Inside focal point (F’)
• Virtual and upright
F
F’
Section 14: Lens Math
Lens Math
• The object side is always positive for lenses and
mirror math
• The virtual and real image sides are different for lenses
• The other side of the lens is positive for the image
– The image here would have a positive value
– The image here would have a negative value
di
do
Positive object side
Negative image side
do
di
Positive image side of lens
• To determine the sign of the focal point
• Determine which way the front of the lens curves
or just remember these two facts:
– A convex lens always has a positive focal length
• Curves to the real side of a lens
– A concave lens always has a negative focal length
• Curves to the virtual side of a lens
Negative image and focal
side of lens
Positive image and focal side
of lens
Example 13
When Sally holds a convex lens 1.00 m from a
snow-covered wall, an image of a 5.00 m distant
igloo is projected onto the snow.
a. What is the focal length of the lens?
b. Draw a ray diagram of the situation
F’
F
Example 13
When Sally holds a convex lens 1.00 m from a snow-covered wall, an image of
a 5.00 m distant igloo is projected onto the snow.
a. What is the focal length of the lens?
Example 13
When Sally holds a convex lens 1.00 m from a
snow-covered wall, an image of a 5.00 m distant
igloo is projected onto the snow.
b. Draw a ray diagram of the situation
F’
F
Example 14
A concave lens is placed 5.0 cm in front of a doll.
a) What is the focal length of the lens if the doll’s
image appears 2.0 cm on the same side of the lens?
b) Draw a ray diagram of the situation
F’
F
Example 14
A concave lens is placed 5.0 cm in front of a doll.
a) What is the focal length of the lens if the doll’s
image appears 2.0 cm on the same size of the lens?
Example 14
A concave lens is placed 5.0 cm in front of a doll.
a) What is the focal length of the lens if the doll’s
image appears 2.0 cm on the same size of the lens?
b) Draw a ray diagram of the situation
F’
F
Example 15
A coin collector is looking at a rare coin 1.0 cm
behind a magnifying glass (convex lens) with a
focal length of 5.0 cm.
a. What is the distance to the image?
b. What is the image’s magnification?
Example 15
A coin collector is looking at a rare coin 1.0 cm
behind a magnifying glass (convex lens) with a
focal length of 5.0 cm.
a. What is the distance to the image?
Example 15
A coin collector is looking at a rare coin 1.0 cm
behind a magnifying glass (convex lens) with a
focal length of 5.0 cm.
a. What is the distance to the image?
b. What is the image’s magnification?
-
Intro
1. You are looking at yourself from 5cm away in a concave
mirror that has a focal length of 15cm.
A. What is the distance to the image?
B. What is the magnification?
2. You do the same as in #1 but in a convex mirror
A. What is the distance to the image?
B. What is the magnification?
3. You are looking through a convex lens at an object 5cm
away. The image is projected 15 cm on the same
A. What is the focal length of the lens?
B. What is the magnification?
Intro
1. You are looking at yourself from 5cm away in a concave
mirror that has a focal length of 15cm.
A. What is the distance to the image?
B. What is the magnification?
Intro
2. You do the same as in #1 but in a convex mirror
A. What is the distance to the image?
B. What is the magnification?
Intro
3. You are looking through a convex lens at an object 5cm
away. The image is projected 15 cm on the same
A. What is the focal length of the lens?
B. What is the magnification?
4. A ray of light is coming from a penny at the
bottom of the water and hitting the surface at
an angle of 34ᵒ what is the angle of refraction.
(nair =1.00 nwater =1.33)
4. A ray of light is coming from a penny at the
bottom of the water and hitting the surface at
an angle of 34ᵒ what is the angle of refraction.
(nair =1.00 nwater =1.33)
4. A ray of light is coming from a penny at the
bottom of the water and hitting the surface at
an angle of 34ᵒ what is the angle of refraction.
(nair =1.00 nwater =1.33)
Section 15: Common Optical Instruments
Common Optical Instruments
• Camera- A simple camera consists
of a convex lens and a light
sensitive film
• The diaphragm and shutter
regulates how much light gets to
the film.
• The diaphragm controls the size of
opening the light passes through
• Most cameras use more than one
lens today
Common Optical Instruments
• Telescope- Uses two lenses to enlarge an
image far away.
• You see an image of an image. The eyepiece
lens forms an enlarged virtual image of the
real image formed by the objective lens.
The Eye
• How the eye focuses:
– The ciliary muscle around the eye
changes the shape and thickness of
the lens, which changes the focal
length of the lens
– In both cameras and the eye the image
is inverted. The brain has learned to
turn the image around.
Defects in Vision
• Farsighted (Hyperopia)- trouble focusing on
objects close. The eyeball is too short or the
cornea is too flat.
– Focus is behind the retina without correction
Defects in Vision
• Nearsighted (Myopia)- trouble focusing on
objects far away. The eyeball is too long or
the cornea is too curved.
• Focus is in front of the retina
Fixing defects
• Converging/convex lenses are used to correct
farsightedness.
• Diverging/concave lenses are used to correct
nearsightedness.
Section 15: Dual Nature of Light
Dual Nature of Light
Wave Particle Duality
• Light acts as a wave (through space) and a
particle (when it interacts with matter)
– Waves are energy carried in the disruption of
medium. Have interference patterns when they
go through each other.
– Particles have a mass and could not occupy the
same space.
Remember Interference
• Within an interference pattern wave
amplitudes may be increased, decreased, or
neutralized
Constructive Interference
Causes Reinforcement
Destructive Interference
Causes Cancelation
Interference with Waves in Water
• Reinforcement and cancelation can be seen
here
• Huygens Principle
– Huygens states light acts as a wave
– Every point acts as a source of a new wave
Wave Properties of Light
• Single slit diffraction on visible light.
• Light has Huygens property of a wave
• Light fans out and actually appears wider than
it should be.
Young’s Interference Experiment
• Young further demonstrate the wave
properties of light with a double slit film.
• When a monochromatic light source is used
a pattern of fringes result
• Young shows that light has interference based
on its wave properties
Particle Nature of Light
• Light acts like a stream of particles when it
interacts with matter
• Photoelectric Effect- Ejection of electrons
from certain metals when light falls upon
them.
– Requires a high frequency of light
Dual Nature of Light Video Clip
Section 16: Other Light Phenomenon
Laser Light
• Incoherent light- crests and troughs don’t line
up
• Coherent light- crests and troughs line up
(same frequency, phase, and direction)
• Laser- Produces coherent light with the aid of
a crystal
Laser Light
Light sabers and Laser beams
Rainbows are produced by the
refraction of light
Thin Films
• Light from one side of a bubble cancels out
light from the other side showing color from
white light
• Diffraction Grating can be used to disperse
light into colors like a prism
– A prism used refraction to disperse light
– Diffraction gradients use the interference of light
to produce colors
Diffraction and Polarization Clip
Polarization of Light
• Light is an electromagnetic wave
• These waves produce an electric field at a
right angle to the magnetic field
• Usually the rays are unpolarized which means
they are oscillating in random directions.
Polarized Light
• Some crystals can cause unpolarized light to
pass through and produce polarized light
which has its electromagnetic fields aligned in
the same direction.
• Transmission axis- line along which light is
polarized
• Transmission axis- line along
which light is polarized
• Light at 90º to the transmission
axis cannot pass through.
How polarized sunglasses work
• Glare
– When light reflects off the ground (a horizontal
surface) it is polarized horizontally.
• Sunglasses stop glare
– They are polarized vertically so that horizontal glare
cannot get through