Presentation on theme: "Chapter 13: electromagnetic waves"— Presentation transcript:
1 Chapter 13: electromagnetic waves Section 1- What are electromagnetic waves?
2 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 wavesSound wavesBoth types of waves require matter to travel through (mechanical waves)
3 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, fireAll electromagnetic waves travel at 300,000 km/s in the vacuum of space.
4 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.
5 Electromagnetic waves E. waves usually travel the slowest in solids, and the fastest in gases.MATERIALSPEED (KM/S)VACUUM300,000AIRSLIGHTLY LESS THAN 300,000WATER226,000GLASS200,000
6 SPEED OF SOUND VS. SPEED OF LIGHT 761 MPH(MILES PER HOUR)186,283 MPS (MILES PER SECOND)SOUNDLIGHT
7 CHAPTER 13: THE ELECTROMAGNETIC SPECTRUM Section 2-The Electromagnetic Spectrum
8 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.
9 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 raysE. waves are described by different names depending on their frequency and wavelength.
12 The electromagnetic spectrum Lowest frequencyWavelengths greater than 1mmUsed with radio, radar, and Magnetic Resonance Imaging (MRI—alternative to x-rays)Low frequencyWavelengths less than 1mUsed with cell phones, satellite signals, and microwave ovensRADIO WAVESMICROWAVES
14 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
22 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.
23 The electromagnetic spectrum Low frequencyWavelengths between 1mm and 750 billionths of a meterEvery object emits infrared waves—hotter objects emit more than cooler objectsEXAMPLES—TV remote, fire, computer, GLOBAL WARMING (i. waves used to read cd’s)Middle frequencyWavelengths range from 400 billionths to 750 billionths of a meterThe only portion of the spectrum that is detected without an instrumentINFRAREDVISIBLE LIGHT
25 The electromagnetic spectrum—ultraviolet waves High frequencyWavelengths from 400 billionths to 10 billionths of a meterUV waves are energetic enough to enter skin cells!
26 THE ELECTROMAGNETIC SPECTRUM Over exposure is unhealthy—can cause sunburn, skin damage, and skin cancerOZONE layer—stratosphere (composed of 3 oxygen atoms)—vital to life on Earth, because it absorbs most of the Sun’s harmful UV wavesMany 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 suppliesMake some materials fluoresce—police use f. powder to show fingerprintsUSEFUL UV’SHARMFUL UV’S
28 The electromagnetic spectrum Very high frequencyCan travel through matterEXAMPLES—Doctors, dentists, airportsHighest frequencyCan travel through matterEXAMPLES—Radiation therapy, radioactive material (U-235)X-RAYSGAMMA RAYS
31 Chapter 13: electromagnetic waves Section3—RADIO COMMUNICATION
32 RADIOEach 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)
33 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)
34 AM VS. FM AM—MODIFYING AMPLITUDE (FREQENCY IS CONSTANT) FM—MODIFYING FREQUENCY (AMPLITUDE IS CONSTANT)
35 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 = FMImage = AM (CRT)
36 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 timeUse radio and microwavesTransceiver—transmits and receives radio signals (use 2 frequencies to allow you to talk and listen at the same timeCELL PHONESPAGERS
37 COMMUNICATIONS SATELLITES Currently more than 2,000 satellites orbit EarthWhat are satellites used for?CommunicationsWeatherMilitaryTVRadioGPS (Global Positioning System)--Navigation
38 SatellitesA 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
39 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 ELEVATIONUSES MICROWAVES
40 GPSOwned 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 hikersMany automobile GPS receivers come with…color display screens/maps, mileage to locations, and info for next exit