Transcript LIGHT - Coosa High School

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WAVES & LIGHT
Waves carry energy from one place to
another
NATURE OF WAVES
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
Waves (Def.) – A wave is a disturbance that
transfers energy from one point to another.

Medium – Substance or region through which
a wave is transmitted.

Speed of Waves – Depends on the properties
of the medium.
Transverse Waves
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 Light
and Electromagnetic
Compression or Longitudinal
Waves
Sound
Waves cont’d
LIGHT: What Is It?
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Light Energy
 Atoms
As atoms absorb energy, electrons jump
out to a higher energy level.
Electrons release light when falling
down to the lower energy level.
 Photons - bundles/packets of energy
released when the electrons fall.
 Light: Stream of Photons

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Properties and Sources of Light

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Light travels almost unimaginably fast and far.
Light carries energy and information.
Light travels in straight lines.
Light bounces and bends when it comes in contact with
objects.
 Light has color.
 Light has different intensities, it can be bright or dim.
The speed of light
 The speed at which light travels through air is
approximately 300 million meters per second.
 Light travels almost a million times faster than
sound.
Electromagnetic Spectrum
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Electromagnetic Spectrum
Spectrum – Light we can see
 Roy G. Biv – Acronym for Red,
Orange, Yellow, Green, Blue, Indigo, &
Violet.
 Largest to Smallest Wavelength.
 Visible
Radio Waves

Invisible Spectrum
 Longest wavelength &
lowest frequency.
 Also emitted by Stars
and gases

Dangers:
 Radio
wave
sickness
 Cancers
leukemia
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Modulating Radio Waves
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
AM –
 Carries audio for T.V. Broadcasts
Longer wavelength so can bend
around hills
 FM –
Carries video for T.V. Broadcasts
Infrared Rays

Invisible Spectrum (Cont.)
Light rays with longer wavelength than red light.
 Our skin emits infrared rays
 Far infrared = hot ; Shorter infrared = cool
 Uses: Cooking, Medicine, T.V. remote controls,
military – thermal imaging, astronomy and
weather forecasts, heat lamps for sports medicine
 Dangers

 Too
much exposure = overheating
Infrared: Thermal Imaging
Microwaves
 Basically high frequency radio waves
 Used in satellite communication and transmission, radar
systems and microwave cooking/microwave oven
 travels in straight line without losing much of its energy
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Dangers:
Prolonged exposure
causes cataracts
Cell phones may cause
Brain damage
(tumors)
satellite station
speed-monitoring
radar
Ultraviolet Rays

Invisible spectrum (cont.).

Humans can’t see, but some insects can

EM waves with frequencies slightly higher than visible light

USES: tanning beds, astronomy, food processing & hospitals to kill germs,
attracts insects (kills them), detecting counterfeit money, whitening teeth,
hardening dental fillings, black light, helps your body produce Vitamin D

Ozone layer blocks most UV from getting to earth

DANGERS:

UV-B CHANGES DNA IN CELLS
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CANCER
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SKIN AND EYE DAMAGE, SUNBURN
X-RAYS
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Invisible Spectrum

High frequency waves

An X-ray machine works by firing a beam of electrons at a
"target". If we fire the electrons with enough energy, X-rays
will be produced.

Uses: Medicine – Bones absorb x-rays; soft tissue does
not., airport security, astronomy

Lead absorbs X-rays
Dangers:
 Cancer,
Cell damage esp. in first trimester for fetus
AIRPORT X-RAY MACHINE
GAMMA RAYS
 Invisible
spectrum (cont.)
 Highest
frequency EM waves; Shortest
wavelength. They come from outer space.
 Uses:
cancer treatment, radioactive tracers,
sterilize foods through irradiation.
 Dangers:
 Kills
all living cells
 Causes

cancer
Only lead or concrete will block
Visible light
 Seen by the human eye
 Uses: fiber optics, medical
procedures, telecommunications,
chemical spectral analysis and
photosynthesis, endoscopy.
Lasers for medical, industrial and
surveying use.
 CD's and DVD's, Laser printers,
Dangers: Too much light can
damage retina
laser surgery
Visible Light cont’d
Process of transforming light, water and
carbon dioxide into glucose and oxygen.
LIGHT: Refraction of Light

Refraction – Bending of light due to a
change in speed.
 Index of Refraction – Amount by which a
material refracts light.
 Prisms – Glass that bends light. Different
frequencies are bent different amounts &
light is broken out into different colors.
Refraction (Cont.)
Refraction cont’d
 Another example of
refraction of light is the
twinkling of a star in the
night sky
 As starlight travels from
space into the Earth’s
atmosphere, the rays are
refracted.
 Since the atmosphere is
constantly changing, the
amount of refraction also
changes.
Color of Light
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Transparent Objects:
 Light transmitted because of no scattering
 Color transmitted is color you see. All
other colors are absorbed.
 Translucent:
 Light is scattered and transmitted some.
 Opaque:
 Light is either reflected or absorbed.
 Color of opaque objects is color it reflects.

OPAQUE
16.2 Color and Vision
 When all the colors of the rainbow are combined, we
do not see any particular color.
 We see light without any color.
 We call this combination of all the colors of light
"white light".
16.2 Color and Vision
 We can think of different
colors of light like balls with
different kinetic energies.
 Blue light has a higher
energy than green light, like
the balls that make it into
the top window.
 Red light has the lowest
energy, like the balls that
can only make it to the
lowest window.
How the human eye sees color
 The retina in the back of
the eye contains
photoreceptors.
 These receptors release
chemical signals.
 Chemical signals travel to
the brain along the optic
nerve.
optic nerve
Photoreceptors in the eye
 Cones respond to
three colors: red,
green and blue.
 Rods detect intensity
of light: black, white,
shades of gray.
How we see colors
 Which chemical
signal gets sent
depends on how
much energy the
light has.
 If the brain gets a
signal from ONLY
green cones, we see
green.
16.2 How we see other colors
 The three color receptors in
the eye allow us to see
millions of different colors.
 The additive primary colors
are red, green, and blue.
 We don’t see everything
white because the strength
of the signal matters.
 All the different shades of
color we can see are made
by changing the proportions
of red, green, and blue.
16.2 How we see the color of things
When we see an object, the
light that reaches our
eyes can come from two
different processes:
1. The light can be emitted
directly from the object,
like a light bulb or glow
stick.
2. The light can come from
somewhere else, like the
sun, and we see the
objects by reflected light.
16.2 How we see the color of things
 Colored fabrics and paints
get color from a
subtractive process.
 Chemicals, known as
pigments, in the dyes and
paints absorb some colors
and allow the color you
actually see to be
reflected.
 Magenta, yellow, and cyan
are the three subtractive
primary colors.
16.2 Why are
plants green?
 Plants absorb energy
from light and convert it
to chemical energy in the
form of sugar (food for
the plant).
 Chlorophyll is an
important molecule that
absorbs blue and red
light.
How You See…again
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Retina –
 Lens refracts light to converge on the
retina. Nerves transmit the image
 Rods –
 Nerve cells in the retina. Very
sensitive to light & dark
 Cones –
 Nerve cells help to see color

Human Eye Diagram
LIGHT & ITS USES
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 Sources
of Light
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Electric Light
 The process of making light with heat is called
incandescence.
 Incandescent bulbs generate light when electricity
passes through a thin piece of metal wire called a
filament.
 The filament heats up and
gives off light.
Electric Light
 The other common kind of electric light is the
fluorescent bulb.
 Fluorescent bulbs
convert electricity
directly to light
without generating a
lot of heat.
 Fluorescent bulbs
use high-voltage
electricity to
energize atoms of
gas that fill the bulb.
Compact Fluorescent lights
Energy Efficient
 Designed to replace incandescent lights
 Must be disposed of properly
 DANGERS:
Mercury poisoning
Destroys neurons

LIGHT & ITS USES - Neon

Neon light – neon gas
inside glass tubes

Electrodes on each end
bounce off electrons and
make red light.

Other gases make other
colors. Krypton – blue
and Argon - purple
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Light Emitting Diodes: LED
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•
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•
•
Tiny bulbs that fit on a circuit
No filament
Do not emit heat
Illuminates by movement of electrons
More costly, but VERY energy efficient
Long life-span
USES: digital clocks, traffic lights, TV,
remote controls – basically anywhere
Light carries energy and power
 Light is a form of energy that travels.
 The intensity of light is the amount of energy per
second falling on a surface.
 Most light sources distribute their light equally in
all directions, making a spherical pattern.
 Because light spreads out in a sphere, the
intensity decreases the farther you get from the
source.
LIGHT & ITS USES - Reflection
 Reflection
waves
– Bouncing back of light
LIGHT & ITS USES:
Reflection Vocabulary
Image –
 Can be projected onto a screen
because light actually passes through
the point where the image appears
 Always inverted
 Real
LIGHT & ITS USES:
Reflection Vocabulary
 Virtual
Image–
 “Not Real” because it cannot be
projected
 Formed in locations where light
does NOT reach
 Image only seems to be there!
Light & Its Uses:
Mirrors
 Reflection
Vocabulary
 Optical Axis – Base line through the
center of a mirror or lens
 Focal Point – Point where reflected or
refracted rays meet & image is formed
 Focal Length – Distance between
center of mirror/lens and focal point
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LIGHT & ITS USES: Mirrors

Plane Mirrors – Perfectly flat
 Actually a Virtual Image
 Erect – Image is right side up
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LIGHT & ITS USES: Mirrors
 Reflection
& Mirrors (Cont.)
 Convex Mirror
Curves outward
Reduces images.
 Uses: Rear view mirrors, store
security…
CAUTION! Objects are closer than they appear!
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LIGHT & ITS USES: Lenses
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Convex Lenses
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Thicker in the center than edges.
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Lens that converges (brings together) light rays.
LIGHT & ITS USES: Lenses
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Lenses –
 Lens that is thicker at the edges and
thinner in the center.
 Diverges light rays
 All images are erect and enlarged.
 Concave
CONVEX
CONCAVE
How You See

Near Sighted –
Eyeball is too long and
image focuses in front
of the retina

Far Sighted –
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Eyeball is too short so
image is focused
behind the retina.
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LIGHT & USES: Lenses
Vision – Human Eye is a convex lens.

Nearsightedness – Concave lenses expand focal lengths

Farsightedness – Convex lenses shortens the focal
length.
LIGHT & USES: Optical Instruments
 Cameras
 Telescopes
 Microscopes
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LIGHT & USES: Optical Instruments

LASERS
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Holography – Use of Lasers to create 3-D images

Fiber Optics – Light energy transferred through long,
flexible fibers of glass/plastic

Uses – Communications, medicine, t.v. transmission, data
processing.
Light carries information
 The fiber-optic networks you read about are
pipelines for information carried by light.
Light carries information
 In some cities, a fiberoptic cable comes
directly into homes
and apartments
carrying telephone,
television, and
Internet signals.
LIGHT & USES: Diffraction

Diffraction – Bending of waves around the edge of a barrier.
Breaks images into bands of light & dark and colors.

Each element has it's own unique 'fingerprint' of color

Scientist identify stars based on the color emitted