Section 1- What are electromagnetic waves?
WHAT DO CORDLESS PHONES AND
MICROWAVE OVENS HAVE IN COMMON?
Each emits electromagnetic waves.
Remember…
A wave is a repeating disturbance or movement
that transfers energy through matter or space.
EXAMPLE…
Water waves
Sound waves
Both types of waves require matter to travel
through (mechanical waves)
Electromagnetic waves
Electromagnetic waves are made by vibrating
electric charges and can travel through space
where matter is not present.
The energy carried by electromagnetic waves is
called radiant energy. EXAMPLE--Sun, fire
All electromagnetic waves travel at 300,000 km/s
in the vacuum of space.
Electromagnetic waves
Because light is an electromagnetic wave, the
speed of electromagnetic waves in space is usually
called “the speed of light.”
However, when electromagnetic waves travel
through matter, they slow down.
The speed of a wave depends upon the material
they travel through.
Electromagnetic waves
E. waves usually travel the slowest in solids, and
the fastest in gases.
MATERIAL
SPEED (KM/S)
VACUUM
AIR
WATER
300,000
GLASS
SLIGHTLY LESS THAN 300,000
226,000
200,000
SPEED OF SOUND VS.
SPEED OF LIGHT
 761 MPH
(MILES PER
HOUR)
186,283 MPS
(MILES PER
SECOND)
SOUND
LIGHT
Section 2The Electromagnetic Spectrum
The electromagnetic spectrum
Electromagnetic waves have a wide variety of
frequencies…They might vibrate once each second
or trillions of times each second.
The entire range of electromagnetic wave
frequencies is known as the electromagnetic
spectrum.
Various portions of the e. spectrum interact with
matter differently. As a result, they are given
different names.
The electromagnetic spectrum
The e. waves that humans can detect with their eyes,
called visible light, are a very small portion of the
entire e. spectrum.
Devices have been built to detect other frequencies.
EXAMPLE--Radio antenna—detects radio waves;
Geiger counter—detects gamma rays
E. waves are described by different names depending
on their frequency and wavelength.
The electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum
 Lowest frequency
 Low frequency
 Wavelengths greater
 Wavelengths less than
than 1mm
 Used with radio, radar,
and Magnetic
Resonance Imaging
(MRI—alternative to xrays)
RADIO WAVES
1m
 Used with cell phones,
satellite signals, and
microwave ovens
MICROWAVES
tECHNOLOGY
RADIO--MRI
MICRO—CELL TOWER
Radio waves--radar
Radar stands for Radio Detecting And Ranging.
RADAR detects the position and movement of
objects.
Radio waves are transmitted toward an object,
bounce off the object and return to a receiving
antenna. By measuring the time required, the
location of the object can be found.
(REFLECTION)
Where is RADAR used? Law enforcement;
tracking aircraft, watercraft, spacecraft; weather;
and sports
TECHNOLOGY
INFRARED--PHOTO
INFRARED—HEAT SENSORS
The Greenhouse effect
“Things that normally happen in geologic time are
happening during the span of a human lifetime.”national
geographic-september 2004
CO2--#1 GREENHOUSE GAS
Since 1979, ice has decreased 9%
per decade.
Temperature rising--infrared
ICE MELTING--INFRARED
SEA LEVEL RISING
WEATHER TURNING WILD--INFRARED
Male—island capital of the maldives/indian ocean—If sea level
rises 3 feet, they could be under water by the end of the century.
The electromagnetic spectrum
 Low frequency
 Middle frequency
 Wavelengths between
 Wavelengths range
1mm and 750 billionths of
a meter
 Every object emits
infrared waves—hotter
objects emit more than
cooler objects
 EXAMPLES—TV remote,
fire, computer, GLOBAL
WARMING (i. waves used
to read cd’s)
INFRARED
from 400 billionths to
750 billionths of a
meter
 The only portion of the
spectrum that is
detected without an
instrument
VISIBLE LIGHT
TECHNOLOGY
VISIBLE LIGHT—LIGHT BULB-INDOOR
VISIBLE LIGHT---LIGHT BULB-OUTDOOR
The electromagnetic
spectrum—ultraviolet waves
 High frequency
 Wavelengths from 400 billionths to 10 billionths
of a meter
 UV waves are energetic enough to enter skin cells!
THE ELECTROMAGNETIC
SPECTRUM
Over exposure is
 Some exposure is

healthy—enables body
to make Vitamin D
(needed for healthy
bones and teeth)
 Ability to kill bacteria
on food or medical
supplies
 Make some materials
fluoresce—police use f.
powder to show
fingerprints
unhealthy—can cause
sunburn, skin damage,
and skin cancer
 OZONE layer—
stratosphere (composed of
3 oxygen atoms)—vital to
life on Earth, because it
absorbs most of the Sun’s
harmful UV waves
 Many countries are
reducing their use of
OZONE depleting
chemicals (labels—NO
CFC’S—
Chlorofluorocarbons)
USEFUL UV’S
HARMFUL UV’S
TECHNOLOGY
UV--FINGERPRINTS
UV-PROTECTION—GLASS,
SUNSCREENS
The
electromagnetic
spectrum
 Very high frequency
 Highest frequency
 Can travel through
matter
 EXAMPLES—Doctors,
dentists, airports
X-RAYS
 Can travel through
matter
 EXAMPLES—Radiation
therapy, radioactive
material (U-235)
GAMMA RAYS
TECHNOLOGY
X-RAY--MEDICAL
X-RAY--AIRPORT
TECHNOLOGY
GAMMA RAYS (U-235)—NUCLEAR
POWER PLANT
GAMMA RAYS—NUCLEAR
MEDICINE—RADIATION THERAPY
Section3—RADIO
COMMUNICATION
RADIO
 Each station is assigned to broadcast at one
particular radio frequency.
 The specific frequency of the e. wave that a
radio station is assigned to is called the
carrier wave.
 EXAMPLE--The carrier wave = 100.1 FM
(100.1mHz)—100,100,000 cycles per second;
the carrier wave can be AM (amplitude
modulation) or FM (frequency modulation)
FM—FREQUENCY
MODULATION
AM—AMPLITUDE
MODULATION
•FM—88mHz to 108mHz
(mHz—millions of cycles
per second)
•AM—535kHz to
1605kHz
(kHz—thousands of
cycles per second)
(CYCLES OR
WAVELENGTHS)
AM VS. FM
AM—MODIFYING AMPLITUDE
(FREQENCY IS CONSTANT)
FM—MODIFYING FREQUENCY
(AMPLITUDE IS CONSTANT)
Television
 TV and radio




transmissions are
similar.
At TV stations, sound
and images are
changed into electric
signals.
These signals are
broadcast by carrier
waves (AM/FM).
Audio = FM
Image = AM (CRT)
Cell phones and pagers
 Use radio and
 Use radio and
microwaves
 TRANSCEIVER—
transmits and receives
radio signals (use 2
frequencies to allow
you to talk and listen
at the same time
microwaves
 Transceiver—transmits
and receives radio
signals (use 2
frequencies to allow
you to talk and listen
at the same time
CELL PHONES
PAGERS
COMMUNICATIONS SATELLITES
 Currently more than 2,000 satellites orbit Earth
 What are satellites used for?
1. Communications
2. Weather
3. Military
4. TV
5. Radio
6. GPS (Global Positioning System)--Navigation
Satellites
 A station broadcasts a
high frequency
microwave signal to
the satellite.
 The satellite receives
the signal, amplifies it,
and transmits it back
to Earth.
 The ground receiver
dishes are rounded to
help focus the
microwaves.
GROUND RECEIVER DISH
Global Positioning System (GPS)
 GPS is a system of 24
satellites, 5 ground
monitoring stations, and
numerous receivers that
provide details about
your exact location at or
above Earth’s surface.
LATITUDE, LONGITUDE, AND
ELEVATION
USES MICROWAVES
GPS
 Owned and operated by the U.S. Department of
Defense, but the microwave signals they send out
can be used by anyone.
 EXAMPLES—Airplanes, ships, cars, and hikers
 Many automobile GPS receivers come with…color
display screens/maps, mileage to locations, and
info for next exit