Chapter 13: electromagnetic waves

Chapter 13: electromagnetic wavesSection 1- What are electromagnetic waves?WHAT DO CORDLESS PHONES AND MICROWAVE OVENS HAVE IN COMMON?Each emits electromagnetic waves.

RememberA wave is a repeating disturbance or movement that transfers energy through matter or space.EXAMPLEWater waves Sound wavesBoth types of waves require matter to travel through (mechanical waves)Electromagnetic wavesElectromagnetic 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 wavesBecause 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 wavesE. waves usually travel the slowest in solids, and the fastest in gases.

MATERIALSPEED (KM/S)VACUUM300,000AIRSLIGHTLY LESS THAN 300,000WATER226,000GLASS200,000SPEED OF SOUND VS. SPEED OF LIGHTSOUNDLIGHT761 MPH(MILES PER HOUR)186,283 MPS(MILES PER SECOND)CHAPTER 13: THE ELECTROMAGNETIC SPECTRUMSection 2-The Electromagnetic SpectrumThe electromagnetic spectrumElectromagnetic waves have a wide variety of frequenciesThey 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 spectrumThe 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 antennadetects radio waves; Geiger counterdetects gamma rays

E. waves are described by different names depending on their frequency and wavelength.The electromagnetic spectrum

Electromagnetic spectrum

The electromagnetic spectrumRADIO WAVESMICROWAVESLowest frequencyWavelengths greater than 1mmUsed with radio, radar, and Magnetic Resonance Imaging (MRIalternative to x-rays)Low frequencyWavelengths less than 1mUsed with cell phones, satellite signals, and microwave ovenstECHNOLOGYRADIO--MRIMICROCELL TOWER

Radio waves--radarRadar 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

TECHNOLOGYINFRARED--PHOTOINFRAREDHEAT SENSORS

The Greenhouse effect

Things that normally happen in geologic time are happening during the span of a human lifetime.national geographic-september 2004CO2--#1 GREENHOUSE GASSince 1979, ice has decreased 9% per decade.

Temperature rising--infrared

ICE MELTING--INFRARED

SEA LEVEL RISINGWEATHER TURNING WILD--INFRARED

Maleisland capital of the maldives/indian oceanIf sea level rises 3 feet, they could be under water by the end of the century.

The electromagnetic spectrumINFRAREDVISIBLE LIGHTLow frequency Wavelengths between 1mm and 750 billionths of a meterEvery object emits infrared waveshotter objects emit more than cooler objectsEXAMPLESTV remote, fire, computer, GLOBAL WARMING (i. waves used to read cds)Middle frequencyWavelengths range from 400 billionths to 750 billionths of a meterThe only portion of the spectrum that is detected without an instrument

TECHNOLOGYVISIBLE LIGHTLIGHT BULB--INDOORVISIBLE LIGHT---LIGHT BULB--OUTDOOR

The electromagnetic spectrumultraviolet wavesHigh frequency

Wavelengths from 400 billionths to 10 billionths of a meter

UV waves are energetic enough to enter skin cells!THE ELECTROMAGNETIC SPECTRUMUSEFUL UVSHARMFUL UVSSome exposure is healthyenables body to make Vitamin D (needed for healthy bones and teeth)Ability to kill bacteria on food or medical suppliesMake some materials fluorescepolice use f. powder to show fingerprints

Over exposure is unhealthycan cause sunburn, skin damage, and skin cancerOZONE layerstratosphere (composed of 3 oxygen atoms)vital to life on Earth, because it absorbs most of the Suns harmful UV wavesMany countries are reducing their use of OZONE depleting chemicals (labelsNO CFCSChlorofluorocarbons)TECHNOLOGYUV--FINGERPRINTSUV-PROTECTIONGLASS, SUNSCREENS

The electromagnetic spectrumX-RAYSGAMMA RAYSVery high frequency

Can travel through matter

EXAMPLESDoctors, dentists, airports

Highest frequency

Can travel through matter

EXAMPLESRadiation therapy, radioactive material (U-235)TECHNOLOGYX-RAY--MEDICALX-RAY--AIRPORT

TECHNOLOGYGAMMA RAYS (U-235)NUCLEAR POWER PLANT GAMMA RAYSNUCLEAR MEDICINERADIATION THERAPY

Chapter 13: electromagnetic wavesSection3RADIO COMMUNICATIONRADIOEach 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)FMFREQUENCYMODULATION

AMAMPLITUDE MODULATIONFM88mHz to 108mHz(mHzmillions of cycles per second)AM535kHz to 1605kHz(kHzthousands of cycles per second)

(CYCLES OR WAVELENGTHS)

AM VS. FMAMMODIFYING AMPLITUDE (FREQENCY IS CONSTANT)FMMODIFYING FREQUENCY (AMPLITUDE IS CONSTANT)

TelevisionTV 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 = FMImage = AM (CRT)

Cell phones and pagersCELL PHONESPAGERSUse radio and microwavesTRANSCEIVERtransmits and receives radio signals (use 2 frequencies to allow you to talk and listen at the same timeUse radio and microwavesTransceivertransmits and receives radio signals (use 2 frequencies to allow you to talk and listen at the same time

COMMUNICATIONS SATELLITESCurrently more than 2,000 satellites orbit EarthWhat are satellites used for?CommunicationsWeatherMilitaryTVRadioGPS (Global Positioning System)--NavigationSatellitesA 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 DISHGlobal Positioning System (GPS)LATITUDE, LONGITUDE, AND ELEVATIONUSES MICROWAVESGPS is a system of 24 satellites, 5 ground monitoring stations, and numerous receivers that provide details about your exact location at or above Earths surface.

GPSOwned and operated by the U.S. Department of Defense, but the microwave signals they send out can be used by anyone.

EXAMPLESAirplanes, ships, cars, and hikers

Many automobile GPS receivers come withcolor display screens/maps, mileage to locations, and info for next exit