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Light & the Electromagnetic
Spectrum
Chapter 25
25-1 Electromagnetic Waves
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I can describe the nature of an
electromagnetic wave.
I can explain how electromagnetic
waves differ from other waves.
Nature of an Electromagnetic Wave (EM)
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EM waves consist of both an electric
field and a magnetic field.
There is a push or pull of charged
particles and magnets.
Travel as transverse waves, fields
are at right angles to the direction of
motion of the wave.
Nature of EM Waves
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Carry energy from one place to
another.
Matter does NOT vibrate, the electric
and magnetic fields vibrate.
Can travel
without a
medium.
Production and Transmission of
Electromagnetic Waves
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Atom: nucleus with protons and
neutrons surrounded by electrons
Electrons are constantly moving.
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Electrons are negatively
charged particles that
produce the electric and
magnetic fields.
Production of EM Waves
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Electrons move back and forth
creating electric and magnetic fields
that move back and forth (vibrate).
The source of all electromagnetic waves
is charge that is changing speed or
direction.
Visible Light
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Visible Light is produced by electrons
jumping between different positions in
an atom.
Electrons gain energy,
jump energy levels,
fall back down
and release energy.
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Types of Electromagnetic Waves
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Light, X-rays, Gamma rays
Speed of all EM waves is the same:
300,000,000 m/s in a vacuum =
speed of light
Light travels slower in air and glass.
Nothing in the universe travels faster
than light.
25-1 Electromagnetic Waves
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I can describe the nature of an
electromagnetic wave.
I can explain how electromagnetic
waves differ from other waves.
Book Work
Electromagnetic
Wave
Modulation
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25.1 Section Review
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Page 645
# 1-5
25.1 Worksheet
Electromagnetic
Spectrum
25-2 The Electromagnetic Spectrum
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I can identify the parts of the
electromagnetic spectrum.
I can describe the uses of
electromagnetic waves of different
frequencies.
I can explain the relationship
between wavelength and frequency.
EM Waves
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EM waves are arranged in order of
wavelength and frequency in what is
known as the electromagnetic
spectrum.
Waves with short wavelengths have high
frequencies, because they all travel at the
same speed both wavelength and
frequency changes.
Let’s make a poster
For the assigned type of EM wave include:
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Name of type of wave energy
Where does it come from
Where it falls in the EM spectrum
Uses of the energy
Dangers of the energy
Two interesting facts
EM waves
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The amount of energy increases
when frequency increases.
The visible
section is
just a small
region with
all the colors.
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Radio Waves
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Lowest frequencies
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Longest wavelength
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Not the same as sound waves.
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Radio waves transmit information
from the antenna of a broadcasting
station to the antenna on your radio
or television
Radio Waves
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Modulation - the radio waves vary in either
amplitude or frequency.
AM = amplitude modulation
FM = frequency modulation
Sent through the air as electrical signals and
in a pattern of changes in amplitude or
frequency.
Once picked up by TV/Radio they are changed
back into their original form.
Radio Waves
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Most sound portions of TV are
carried as AM waves and most
pictures are carried as FM waves.
Can be disturbed by obstacles or
weather conditions.
TV cables protect the waves from
interferences.
Radio Waves
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Medicine: can vibrate parts
of the brain to look at it
without harming the cells –
called magnetic resonance
imaging. (MRI)
Astronomy: used
in telescopes
because they can
travel through space.
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MRI of the Brain
Microwaves
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Highest frequency radio waves.
Advantage: Heats food in short amount of
time without heating the dish.
Water and molecules in food absorb the
energy (heat) from microwaves but dishes do
not.
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Metals can absorb the energy – that is why you
do not put metal in the microwave oven.
They are also used in cell phones and
weather forecasting.
Microwave use: Radar
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Short wavelength microwaves are used in
radar.
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Radar = radio detecting and ranging
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Used to locate objects and monitor speed.
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Works just like sonar
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Monitors positions of airplanes, ships at sea,
satellites orbiting the earth, track storms
Infrared Rays
Infrared rays have slightly
lower frequencies than
visible light.
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Not seen but felt as heat.
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50% of the suns rays are infrared
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All objects give off infrared rays, the
amount depends on the
temperature of the object.
Infrared Rays
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Warm objects give off infrared rays.
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Cool objects absorb infrared rays and
become warmer.
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Infrared camera take pictures of heat
instead of light so can be used at night.
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Medicine: unhealthy tissue becomes hotter
than healthy tissue.
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Can determine if art is real or fake by
looking at paints.
Visible Spectrum
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Light you can see = visible light
Half of the energy given off by the sun
is in the form of visible light.
Visible light is
used when plants
make food
(photosynthesis).
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Ultraviolet Rays
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Ultraviolet rays – frequency just
higher than visible light
Have enough energy to kill living
cells.
Used to kill germs in hospitals and
destroy bacteria and preserve food.
Ultraviolet Rays (UV)
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Humans can not see them but many insects
can.
They are what cause sunburn.
Over exposure to UV rays can cause serious
damage to the skin, eyes and immune
system.
Ozone in the atmosphere absorbs most of the
sun’s damaging UV rays before they reach the
earth.
X-rays
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X-rays with frequencies just
above UV rays
Enough energy to pass easily
through many materials,
including skin.
Denser material absorb x-rays.
Bones absorb x-rays and on
the pictures show up as white
areas.
X-rays
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Even though useful in medical
diagnosis, they have a potential
health hazard.
Large amounts of x-rays over a
lifetime can cause defects in cells.
Gamma Rays
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Gamma rays – highest frequency and
shortest wavelengths
Can go through 3 meters of concrete.
Excessive exposure to gamma rays can
cause severe illness.
Gamma cameras can be used to detect
injected fluid that emits gamma rays in
the body.
Let’s watch a video clip
 Electromagnetic
Spectrum
25-2 The Electromagnetic Spectrum
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I can identify the parts of the
electromagnetic spectrum.
I can describe the uses of
electromagnetic waves of different
frequencies.
I can explain the relationship
between wavelength and frequency.
Terms
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radio wave
radar
x-ray
microwave
gamma ray
infrared ray
visible light
ultraviolet ray
25.2 Section Review
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Page 656
# 1-4
o
25.2 Worksheet
25-3 Visible Light
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I can distinguish between luminous
and illuminated objects.
I can describe incandescent,
fluorescent, and neon light.
I can explain the differences
between hot and cool light.
Visible Light
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Luminous objects – anything that
can give off its own light
Ex: sun, other stars, light bulbs,
campfires, fireflies
Visible Light
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Illuminated objects – an object
that can be seen because it is lit up
Ex: moon, desk, paper, people
Luminous Objects
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Luminous objects can produce light
in 3 different ways:
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1. incandescent light
2. fluorescent light
3. neon light
Incandescent Light
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Incandescent light – produced from
heat
Ordinary light bulbs are hot to touch
after they have been on for a while.
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Light bulbs have tungsten metal inside of
them that heats up and produces light
energy
Coils of a toaster over heat up and glow
red hot
Fluorescent Light
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Cooler light and uses less electricity
than incandescent lights.
Electrons hit gas molecules to lessen
the pressure.
Phosphors (coated on the inside of
the light) absorb UV energy and start
to glow, producing visible light.
Fluorescent Light
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The color of fluorescent lights depend
on the color of the phosphors.
Phosphors are sometimes added to
laundry detergents to make clothes
appear whiter because sunlight
makes them glow.
Neon Lights
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Also cool light like fluorescent lights
Electrons pass through different
types of gases and produce light.
Neon gas = bright red
Mercury gas = greenish-blue
Sodium gas = yellow-orange
25-3 Visible Light
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I can distinguish between luminous
and illuminated objects.
I can describe incandescent,
fluorescent, and neon light.
I can explain the differences
between hot and cool light.
Terms
luminous object
incandescent light
illuminated object
fluorescent light
neon light
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25.3 Section Review
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Page 658
# 1-4
25.3 Worksheet
26-4 Color
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I can account for the color of opaque,
translucent, and transparent objects.
I can predict which colors will be
transmitted, reflected, or absorbed by
various substances.
I can distinguish between colors of light
and colors of pigments.
I can describe polarized light and its
uses.
Why do objects have color?
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White light is broken into its
individual colors by wavelength.
When light strikes any form of
matter, the light can be
transmitted, reflected, or
absorbed.
Transmitted Light
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Transparent - light is transmitted through it,
objects are seen very clear.
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Translucent - light is transmitted through a
substance that scatters the light, the image is
unclear and lacks detail.
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Ex: water, glass, air
Ex: wax paper, frosted glass
Opaque – does not transmit light.
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Ex: block of wood, sheet of metal, black cloth
The Color of Objects
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If an object does not allow any light to
pass through it (opaque), the light is
either reflected or absorbed.
The color of an opaque object is the
color it reflects.
A red apple reflects red and absorbs
all the other colors.
Black and White
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White is the presence of all the colors
of the visible spectrum.
White objects reflect all colors.
Black objects absorb all of the
colors.
Primary Colors of Light
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Primary colors can be mixed to
produce light of any other color.
Primary colors are red, blue, and
green.
Adding different amounts of each
creates different colors.
Red and green light mixed produce
yellow.
Paints are Pigments (not light)
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The primary colors of pigments are
yellow, cyan, and magenta.
When all 3 are mixed evenly, all colors
are absorbed and result in black.
Compare
Pigments (not light)
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Pigments have a certain color because
they can absorb only certain
wavelengths of the visible spectrum.
All the rest are reflected.
All objects contain pigments.
The color of an object is a result of the
pigments it contains.
Polarized Light and Filters
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Sunglasses that reduce glare use
polarized filters.
Light waves vibrate in different
directions at the same time.
A polarizing filter is made up of a large
number of vertical slits.
Light can only pass through a
polarizing filter if they are vibrating
the same as the slits.
Polarized Light and Filters
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Polarized light is light that passes
through the filter.
The rest of the light is reflected or
absorbed.
Sunlight glare is mostly horizontal so
sunglasses are vertically polarized.
26-4 Color
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I can account for the color of opaque,
translucent, and transparent objects.
I can predict which colors will be
transmitted, reflected, or absorbed by
various substances.
I can distinguish between colors of light
and colors of pigments.
I can describe polarized light and its
uses.
Terms
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Transparent
Translucent
Opaque
Polarized light
26.4 Section Review
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Page 684
# 1-5
26.4 Worksheet
Chapter 25 Review – pg 664
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Multiple Choice
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True or False
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1-8
1-6
Concept Master
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1, 3, 7, 8