# Chapter 13: electromagnetic waves

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Chapter 13: electromagnetic waves
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 300,000 AIR SLIGHTLY LESS THAN 300,000 WATER 226,000 GLASS 200,000

SPEED OF SOUND VS. SPEED OF LIGHT
761 MPH (MILES PER HOUR) 186,283 MPS (MILES PER SECOND) SOUND LIGHT

CHAPTER 13: THE ELECTROMAGNETIC SPECTRUM
Section 2- The 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 Wavelengths greater than 1mm Used with radio, radar, and Magnetic Resonance Imaging (MRI—alternative to x-rays) Low frequency Wavelengths less than 1m Used with cell phones, satellite signals, and microwave ovens RADIO WAVES MICROWAVES

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 Wavelengths between 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) Middle frequency Wavelengths range from 400 billionths to 750 billionths of a meter The only portion of the spectrum that is detected without an instrument INFRARED 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 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) 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 USEFUL UV’S HARMFUL UV’S

TECHNOLOGY UV--FINGERPRINTS UV-PROTECTION—GLASS, SUNSCREENS

The electromagnetic spectrum
Very high frequency Can travel through matter EXAMPLES—Doctors, dentists, airports Highest frequency Can travel through matter EXAMPLES—Radiation therapy, radioactive material (U-235) X-RAYS GAMMA RAYS

TECHNOLOGY X-RAY--MEDICAL X-RAY--AIRPORT

TECHNOLOGY GAMMA RAYS (U-235)—NUCLEAR POWER PLANT

Chapter 13: electromagnetic waves

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 = 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 CELL PHONES PAGERS Use radio and microwaves
TRANSCEIVER—transmits and receives radio signals (use 2 frequencies to allow you to talk and listen at the same time Use radio and 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? Communications Weather Military TV Radio 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