Electromagnetic Waves Section O-3.1

The Nature of Electromagnetic Waves What are Electromagnetic Waves Transfer energy from one place to another Don’t need a medium Transverse waves Changing electric and magnetic fields

What are Electric and Magnetic Fields Electric Field is a region where charged particles can be pushed or pulled If there is an electric charge, there is an electric field Electric currents are surrounded by an magnetic field If electric field changes, so does magnetic field

What is Electromagnetic Radiation? Energy transferred by electromagnetic waves. Does not need a medium

What is the speed of electromagnetic waves? Fastest in a vacuum 300,000,000 meters per second 3 x 10 8 meters/second 186,000 miles/second Sun to earth is about 8 minutes Travels slower in medium like air or glass

Are EM Waves or Particles? Has Properties of Both Regular light has transverse waves moving in all directions Polarizing filter limits it waves of one direction Light can also make particles move (like pool balls being hit) Photoelectric effect – makes electrons move Each packet of EM is called a “photon”

Waves of the EM Spectrum O-2.2

What are Characteristics of EM Waves? Travel at the same Speed Different wavelengths Different frequencies EM Spectrum is ragne of EM waves in order of increasing fequency Radio, infrared, visible, ultraviolet, X-rays, gamma rays

The Electromagnetic Spectrum

What are Radio Waves Longest Wavelengths, lowest frequency Radio stations Different stations are at different frequencies

What are MicroWaves? Radio waves with Shortest Wavelengths, highest frequencies Microwave ovens Pass through glass and plastic Bounce off metal

What is Radar? Radio Detection And Ranging Uses reflections of radio waves Like Sonar but with radio waves Used in air and space Now used for weather also.

What is Magnetic Resonance Imaging (MRI)? Use radio waves to produce image of insides of person Radio waves plus strong magnets cause atoms in body to line up along magnetic field. Atoms return to normal at different rates resulting in a picture MRI can show pictures of brain, muscles and ligaments that X-Rays cannot.

What are Infrared Rays? Energy we feel as heat is infrared Short wavelengths Higher frequencies than radio INFRA (Latin) means “below” Next waves in spectrum is red light Thermogram – a picture of different temperatures Night vision goggles Termite detection

What is Visible Light? Visible Light is the light you can see Shorter wavelength and higher frequencies than infrared Visible light goes from red, to orange, yellow, green, blue, violet (indigo) A spectrum shows all the colors of visible lilght A rainbow is a spectrum of visible light

What is Ultraviolet Light Ultraviolet Light is wavelengths shorter than visible light (and higher frequencies) “ultra” (Latin) means above Ultraviolet is frequencies above visible violet light UV Light carries more energy Kills or damages living cells Also causes skin to produce Vitamin D UV Light causes sunburn Different animals (bees, mosquitoes) see infrared or ultraviolet to help them survive

What are X-Rays? X-Rays: very short wavelengths, high frequencies Because of short wavelength, they can penetrate most matter Very dense matter (bone, metal) reflects. X-rays are used to see broken bones Too much exposure to X-Rays can cause cancer Used in industry to find cracks in steel or concrete

What are Gamma Rays? Gamma Rays have shortest wavelength and highest frequency and highest energy. Produced by some nuclear reactions Penetrate almost anything Very dangerous Used in some cancer treatments and by astronomers to detect far-off stars and galaxies

Producing Visible Light O-3.3

How do We Produce Visible Light? What we see is reflected light A light source produces visible light that can reflect off the other objects Common types of Lighting are: Incandescent Fluorescent Neon Sodium vapor Tungsten-halogen

What is Incandescent Light Normal light bulbs Have a small wire (filament) that gets very hot when electricity is applied Filament is made of tungsten When hot enough, incandescent bulbs give off light in all the colors of the spectrum Not very efficient Also give off a lot of heat (energy that is not converted to light)

What are Fluorescent Lights? Long Narrow Tubes Frequently found in schools and businesses Contains a gas and inside is coated with a powder Electricity causes the gas to emit ultraviolet waves. Powder coating converts ultraviolet to visible light More efficient than incandescent More light, less heat Light tends to be more in the blue range Can irritate contact lens wearers

What are Neon Lights? Long tubes filled with neon Electricity makes the neon gas glow RED Different colors are different gases or mixtures Argon and mercury vapor produce bluish green light Helium gives off yellow light Krypton gives off pale violet Use in bright flashy signs (Las Vegas)

What are Sodium Vapor Lights? Small amount of solid sodium, plus neon and argon Electricity causes neon and argon to glow Neon and argon heats up sodium to change into a gas Sodium Vapor gives off yellow/orange light Used for street lighting Very efficient/Use little electricity

What are Tungsten-Halogen Lights Work like Incandescent Have tungsten filaments Bulb is full of halogen gas Filament gets hot and causes halogen to glow bright white Used in Lamps and Headlights Lots of light from small bulbs Get very hot

What is Bioluminescence? Organisms that produce their own light Fireflies Also found in some jellyfish deep in the ocean Used by organisms to find mates and food.

Wireless Communication O-3.4

How Does Radio and TV work? Signals carried on Radio Waves Different stations use different frequencies measured in Kilohertz (KHz) FCC (US GOV) assigns one part of spectrum to radio, another to TV

What is AM Radio AM stands for Amplitude Modulation Music and speech are converted into a pattern of amplitude changes in a radio wave

What is FM Radio FM is Frequency Modulation Radio signal travels as changes in frequency Higher frequency than AM

What are Television Waves? Similar to radio but carry pictures also. VHF (very high frequency) = channels 2-13 UHF (ultra high frequency) = channels above 13

How Do Cell Phones Work? Small radio transmitters and recievers High-frequency radio waves Each area divided into ‘cells’ that access a tower Tower has to be in ‘line of sight’ As you move, computers transfer signal from tower to tower

How do Cordless Phones Work? Radio waves go from handset to base station Short distance

How do Pagers Work? You leave a voic Information is coded to a specific pager Voic is send by radio wave to pager

How do Communications Satellites Work? Radio waves sent from earth to satellite. Wave then sent to other parts of earth Satellite phone systems Television satellites GPS (Global Positioning Systems)