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LIGHT
M A Ps
Meaningful Applications of Physical Science
Email: [email protected]
LIGHT
. .
LIGHT
A. Properties of light
B. Absorption
C. Reflection
D. Refraction
E. Application of the Properties of Light
LIGHT
A. Properties Of Light
1. How Is A Radiometer Affected By Light? . . . . . . . . . . . . . . . . .
7
2. Speed Of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3. The Role Of Light In Seeing . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. The Affect Of A Pinhole On Light . . . . . . . . . . . . . . . . . . . . . . . 12
5. Properties Of Shadows . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 16
6. Representing The Behavior Of Light By Drawing Light Rays . . 25
7. A Model Of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
A. What Is A Pulse? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
B. What Are The Properties Of Pulses? . . . . . . . . . . . . . . . . . . 29
C. Light As Waves – Electromagnetic Radiation . . . . . . . . . . . 35
D. Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
LIGHT
B. Absorption
1. Absorption Of Light Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2. Absorption Of Light Energy and the Greenhouse Effect . . . . . . . . . . 46
LIGHT
C. Reflection
1. How Do Things Appear In A Mirror? (Palindromes) . . . . . . 50
2. How Much Of Yourself Can You See In A Mirror? . . . . . . . . . 56
3. Where Is The Mirror Image? (Single Burning Candle, Double Burning Candle) . . . 61
4. How Does Light Reflect? (The Law) . . . . . . . . . . . . . . . . . . 65
Building The Ray Maker, Three Mirrors, Classroom Reflection
Pin Reflection Game, Two Handled Mirror - Three Hands?
Aquarium - Count The Strings
Barber Pole Effect, Peppers Box, Infinity Box
5. How Does Light Reflect From A Non-shiny Surface? . . . . . . 71
6. How Do Curved Mirrors Reflect Light? . . . . . . . . . . . . . . . . . 76
Concave Mirror and The Inverted Light bulb
Circus Mirrors, Mirage (pick up the object)
LIGHT
D. Refraction
1. Transparent, Translucent And Opaque Objects . . . . . . . . . . . . . 81
2. How Does Light Change Direction When Refracted?
. . . . . . . . 82
Ghost Crystals, Oil Immersion Oil, Plastic Rod, Pepsi Bottle Refraction
3. Laws Of Refraction (Plastic Block) . . . . . . . . . . . . . . . . . . . . . . 88
4. Seeing Objects Through Transparent Materials? (Aquarium). . . . . 93
5. Spear Fishing, Mirages And Twinkling Stars . . . . . . . . . . . . . . 99
6. Lenses - Magnifying Lens For Image Production (Pin Hole Camera Extension)
A. Types Of Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
B. Power And Focal Length . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
C. Eye Defects - Nearsightedness And Farsightedness . . . . . 123
D. How To Make A Telescope . . . . . . . . . . . . . . . . . . . . . . . . . 125
LIGHT
E. Application of the Properties of Light
1. Dark Suckers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
2. Transmitted Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Coiled Plastic Rod, Critical Angle demonstration, Fiber optics,
Transmission of Sound by Modulation of Light Energy
3. Polarized light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
We Had A Great Time
Naïve Ideas - Properties of light
1. Light is associated only with either a source or its effects. Light is not
considered to exist independently in space; and hence, light is not
conceived of as “traveling”.
2. The effects of light are instantaneous. Light does not travel with a finite
speed.
3. An object is “seen” because light shines on it. Light is a necessary
condition for seeing an object, but there is no recognition of anything
that moves between the object and the eye.
4. Lines drawn outward from a light bulb in a sketch represent the “glow”
surrounding the bulb.
5. A shadow is something that exists on its own. Light pushes the shadow
away from the object to the wall or ground and is thought of as a “dark”
reflection of the object
6. Light is not necessarily conserved. It may disappear or be intensified.
7. Light from a bulb only extends outward a certain distance, arc then
stops. How far it extends depends on the brightness of the bulb.
7
How is a Radiometer Affected by Light?
A radiometer consists of a set of vanes, each
shiny on one side and blackened on the
other, that is mounted in an evacuated
vessel. When exposed to light, the vanes
revolve. The first radiometer was constructed
to settle the controversy regarding whether
light exerts a force. The idea was that a
reflecting surface would experience a greater
force from the light than an absorbing one.
Unexpectedly, the opposite effect was
observed. The blackened vane retreated from
the light source. We now know that the black
surface is warmer than the shiny one and that
gas molecules will recoil faster from the hot
surface. The slight difference in molecule
recoil is what causes the device to spin.
Speed Of Light Compared to the Speed of Sound
BANG!
Light:
3 x 108 meters per second or 186,000 miles per second
Sound: 330 meters per second or 1100 feet per second.
1
See The Book
1
Spreading Light
0
2
The affect of a pinhole on light
1
3
Pinhole Image
0
Characteristics Of Waves
I. Characteristics Of A Wave
A. Pulse: a single disturbance in a medium.
B. Frequency: the number of occurrences of some event per unit of time.
(example; the number of times the meter stick goes up and down in one minute.)
C. Amplitude: the measurement of the distance the medium moves from the
zero point to the maximum displacement. (example; the distance of the
very end of the meter stick - from standing still to the farthest distance away from
that zero position.)
D. Wavelength: the distance along a wave front — from any starting point
to the next successive starting point. (example; looking at a slinky in motion.
Begin with the very beginning of a pulse to the very beginning of the next pulse .)
E. Loudness: occurs with the addition of energy to the vibrating medium.
Five Basic Characteristics of Waves
Wavelength
Period = .5-sec.
Amplitude
Time = 1 sec
Frequency = 2 Hz
1.
2.
3.
4.
5.
Wavelength (l), is the distance from a point on a wave to the next point
Amplitude (A), is the maximum displacement. Amplitude indicates the loudness of a sound.
Period (t), is the time (in seconds) that it takes for a wave to travel one full wavelength.
Frequency (f), is the number of vibrations (waves) per second. This indicates the pitch of a sound.
Wave speed (V), is the rate the wave is traveling; the units of measurement are meters/sec.
9
FUNdamentals of Waves
II. Components Of Light and Sound waves
A Energy is needed to form any Light or Sound wave.
B Light waves are made by continuous succession of oscillating magnetic and
electric fields. These fields travel as a wave, an EM (Electromagnetic) wave.
C. Sound waves are made by the vibrations (moving back and forth) of the
particles of an object.
D. A medium is NOT needed to transport the Light energy.
E. A medium is needed to transport the Sound energy.
F. Waves are formed when energy is transported from one place to another.
8
FUNdamentals of Waves
III. Three Types Of Waves
A. Torsional waves when the disturbance occurs as a twisting
effect in a plane that is perpendicular to the direction on the
wave motion (examples: twisters, hurricanes, tornados).
B. Longitudinal waves when the disturbance occurs in the same direction of
the wave motion. (examples: sound, people standing in line, cars taking
off from one red light and coming to a stop at another red light.)
C. Transversal waves when the disturbance occurs at right angles to the
direction of the wave motion. (examples: water, light, radio, electromagnetic.)
7
Building a Wave Model
6
Wave Patterns
3
5
http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=28
4
Propagation of Light Energy
3
Wave Properties
2
Construction & Destructive Interference
Constructive Interference
Destructive Interference
1
EM Spectrum
0
Shadows
Illumination
Object
Shadow
Bulb
Illumination
Screen
Illumination
Object
Shadow
Bulb
Illumination
1
3
Multiple Shadows
Full
Illumination
Partial
Shadow
Bulb
Object
Bulb
Full
Shadow
Partial
Shadow
Full
Illumination
Screen
0
1
Absorption of Light Energy
Absorption of Energy and the Greenhouse Effect
Naïve Ideas - Reflection
1. A mirror reverses everything.
2. For an observer to see an object it must be directly in front of the mirror.
3. The position of the observer is not important in determining whether the mirror
image can be seen.
4. An observer can see more of his or her mirror image by moving further back from
the mirror.
5. The mirror image of an object is located on the surface of the mirror. The image
is thought of as a picture on a flat surface.
6. A mirror’s image goes from the object to the mirror’s surface. The observer sees
the image on the mirror surface which is reflected off the mirror.
7. Light reflects from a shiny surface in an random manner.
8. Light is reflected from smooth surface mirrors but not from non-shiny surfaces.
9. Curved mirrors make everything distorted.
9
Palindromes
Words and numbers that read the same forward as backward.
Some Palindromes have symmetry. When a mirror is
placed on the right, of the word, and perpendicular to
the surface the word is read the same in the mirror as
without the mirror.
1
Palindromes
MOM
RACECAR.
EVIL OLIVE.
STEP ON NO PETS
RISE TO VOTE, SIR
DO GEESE SEE GOD?
NEVER ODD OR EVEN.
A DOG! A PANIC IN A PAGODA!
A MAN, A PLAN, A CANAL -- PANAMA!
DRAW, O CAESAR! ERASE A COWARD!
NO, SIR, PANIC IS A BASIC IN A PRISON.
GO HANG A SALAMI. I'M A LASAGNA HOG.
STRESSED? NO TIPS ? SPIT ON DESSERTS.
ARE WE NOT DRAWN ONWARD, WE FEW? DRAWN ONWARD TO NEW ERA?
DOC, NOTE. I DISSENT. A FAST NEVER PREVENTS A FATNESS. I DIET ON COD
0
Mirror Image
2
Single Candle Reflection
A single piece
of plastic is held
in
a
vertical
position by two
support blocks.
When
viewing
from the position
of the lit candle
the reflection, of
the lit candle,
makes the unlit
candle, on the
other side of the
plastic, look lit.
1
Double Candle Reflection
Two pieces of
plastic are held in a
vertical position by
two support blocks.
When viewing from
the position of the
lit candle the two
reflections, one for
each piece of
plastic makes the
unlit candles, on
the other side of
the plastic, look lit.
0
How Much of Yourself Can You See in a Mirror?
Mirror
5
Two Questions:
1. How tall, compared to his actual height, is the man’s image in the mirror?
2. If the man mover two meters further from the mirror what will happen to his image?
1
How Much of Yourself Can You See in a Mirror?
Mirror
7.5-cm
a
b
180.0-cm
90.0-cm
165.0-cm
a
b
82.5-cm
5
Two Questions:
1. How tall, compared to his actual height, is the man’s image in the mirror?
2. If the man mover two meters further from the mirror what will happen to his image?
0
Making Rays of light
5
Making Rays of light
4
Investigating The Law of Reflection
3
The Reflection Game
M idpoint
Normal
Place a pin at the point labeled midpoint. This will hold the mirror in a vertical
position to the cardboard and be used as a reference point. Looking at the
protractor select any number along the outside and place the second pin at
that point. Hold the cardboard at eye level. Move the cardboard until you
discover the position that you can see the first and second pins lined up in
the mirror. When the two pins appear to be lined up in the mirror adjust the
third pin so that all three pins appear to be in a straight line and insert it into
the cardboard at that point. Compare the number, on the protractor, of the
first pin to the third pin.
2
Law of Reflection
Outgoing
Ray Of Light
Incoming
Ray Of Light
Normal
4
Reflecting Surface
1
Law of Reflection
Incident Ray
Angle of
Incidence
Normal
A reference line drawn
perpendicular to the surface at
the point the light ray strikes
Angle of
reflection
Reflected Ray
4
R
E
F
L
E
C
T
I
V
E
S
U
R
F
A
C
E
Angle of Incident = Angle of Reflection
0
Simulator the Light Laboratory
How does light reflect from a non-shiny surface?
Regular & Diffuse Reflection
Regular Reflection
Diffuse Reflection
How Do Curved Mirrors Reflect Light?
3
3
How Do Curved Mirrors Reflect Light?
Concave Mirror
Convex Mirror
2
How Do Curved Mirrors Reflect Light?
Using a Simulator
1
How Do Curved Mirrors Reflect Light?
Using a Simulator
0
Naïve Ideas - Refraction
1. Light shines on a translucent material and illuminates it so that it can be
seen. Light does not travel from the material to the eye.
2. Light always passes straight through a transparent material without
changing direction.
3. When an object is viewed through a transparent solid or liquid material,
the object is seen exactly where it is located.
3
Transparent, Translucent & Opaque
Transparent
Translucent
Opaque
3
How Does Light Change Directions?
Refraction
Transparent Material
Light Ray
Refracted Light Ray
Transparent Material
Light Ray
Transparent Material
Light Ray
Refracted Light Ray
3
Refraction Through A Block
2
Refraction Summary
To determine how a ray of light is
refracted as it passes from one optical
medium to a different optical medium
follow these three steps.
1. Determine the position of the
normal.
1
Normal
Light Ray
Air
Air – Less Dense
2. Determine where the ray of light would
have gone if the medium through which
the light passed had not changed.
3. Determine whether the ray is bent
away from, or towards the normal.
(Greater density toward the normal,
lesser density away from the normal)
3
2
Air
3
Glass – MoreAirDense
In the drawing air has less optical density than glass. The light ray is passing
from a medium of lesser optical density to one of greater optical density. The
light ray will bend towards the normal.
1
A How Does Light Change Directions?
Party Trick Based on the Refraction of Light
CARBON DIOXIDE
Explain that just as a glass prism splits up the different colors of white light, when
different colored light passes through glass; it is also affected to an extent that
depends on its color. Write the words CARBON DIOXIDE on a piece of paper,
CARBON in red and DIOXIDE in blue. Put the paper close behind the stem of a
wine glass, and look at the words through the stem. The red letters turn upside
down, but the blue ones don't.
1
This has nothing to do with the different colors of the words, or of red light being
bent more or less than blue light. The stem of the wine glass turns both words
upside down, but because DIOXIDE is symmetrical about a horizontal line, you
don't notice that it is upside down - it looks just the same either way.
Try the words CHOICE QUALITY.
0
Refraction Analyzed
Air
Water
Air
Normal
Water
Air
Incomming Ray of Light
1
7
Measuring Index of Refraction
Incoming Ray of Light
Normal
Air
Where the light Ray o
would have gone if it was
not refracted
Refracted Ray
of Light
Water
0
Seeing Objects Through Transparent Objects
Refraction - Appearing Coin
3
Seeing Objects Through Transparent Objects
The Distorted Straw
Apparent Position
Actual Position
2
Seeing Objects Through Transparent Objects
Refraction Through a Block
Side View
Actual Pencil
Plexiglas
Block
Virtual image of
Pencil as seen
through the block
1
Seeing Objects Through Transparent Objects
Sight Here to See The Coin
Aim Here to Hit The Coin
Air
Water
Actual Position
of the Coin
Apparent Direction
To the Coin
0
Where Do You Aim
1
Road Mirage
Light From Sky
Observer
Mirage
0
Types of Lenses
Converging Lenses
Diverging Lenses
6
Investigating Convex Lenses
Simulator
5
Image Formation With a Converging Lens
Simulator
4
4
Seeing the Image
3
Image Formation With a Diverging Lens
Simulator
1
2
Investigating Concave Lenses
Simulator
1
Diverging Lens Increases the field
Field of
View
Without Diverging Lens
Field of
View
With Diverging Lens
0
Power & Focal Length
Shorter Focal Length
The lens strength in diopters
is defined as S = 1/f (meters).
Note: Converging lenses are
+ and diverging lenses as - .
Higher
Power
What is the diopter number of
a lens of focal length 0.05
meters?
S = 1 / 0.05 = 20
Longer Focal Length
Lower Power
What is the focal length of a
+7 diopter lens?
S=1/f
fxS=1
f = 1 / S = 1 / 7 = .143-m
Normal Eye
4
Farsighted Eye
3
Nearsighted Eye
2
Nearsighted Eye
Nearsighted Eye
Diverging Corrective Lens
1
Farsighted Eye
Farsighted Eye
Converging Corrective Lens
0
How to make a telescope
1
Simulator - The Light Laboratory
2
How to make a telescope
Simulator
1
Telescopes
Astronomical Telescope
Galilean Telescope
0
Dark
Sucker
s
Transmitted Light - Total Internal Reflection
The light beam stays internal to the water,
continuously reflecting at each boundary.
3
Transmitted Light - Total Internal Reflection
2
Transmitted Light - Coiled Plastic Rod
1
1
Transmission of Sound Through The
Modulation of Light
Amplified
Speaker
Solar
Cell
LED
470 – Ohm
Resistor
9-volt
Battery
Radio or
Tape Recorder
400 – Turn Coil
Wrapped on
Bolt
0
Transmitted Light - Polarized Light
We Had A Great Time