Producing Light Waves

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Terminology

Illuminated – You can see the object because of the light that bounces off of it (reflected light)Moon, planets, cars, people…

Luminous – The object creates lightSun, stars, burning wood, light bulb…

Spectroscope – Measure Light

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Incandescent Lights

A light bulb with a filament inside that glows when hot

Invented by Thomas Edison 1879

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Ordinary Light Bulbs

Thin wire = TungstenWhen hot glows whiteTo prevent burning sealed in glass

Nitrogen and ArgonLess than 10% of energy used to make light90% of energy makes heat (infrared rays)

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Tungsten-Halogen Bulb

Thin wire = TungstenWhen hot glows whiteTo prevent burning sealed in glass

Halogen gasBurns much hotter therefore more lightAlso means much more heat

Severe fire danger

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Fluorescent Lights

Glass tube filled with mercury vaporElectricity causes gas to release ultraviolet raysPowder lines the inside of the tube

Powder hit with UV light then releases visible lightAdvantage

Most light created is visible light (more efficient)Do not get as hot as regular bulbsLasts longer

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Vapor Lights

Bulbs with neon/argon gasMixed with small about of solid sodium/mercuryElectricity is used to heat gasHot gas converts solid into gas which glowsSodium solid = Yellowish lightMercury solid = Bluish lightOften used as street lights/parking lotsNo filament to burn out so long lasting and efficient

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Neon Lights

Clear/colored glass tubeFill with gasElectricity causes gases to glow

Neon = Red lightArgon/mercury = Green/blueHelium = PinkKrypton = Violet

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Wireless Communication

Radio/TVTwo ways to send messages

Amplitude Modulation (AM)Frequency Modulation (FM)

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AM

Less energyBounce off atmosphereLong rangeSend messages in kHzRange 535 – 1605

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FM

High energyPass into spaceShort rangeSend messages in MHzRange 88 – 108

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TV

Very High Frequency (VHF)Range 54 – 216 MHzChannels 2 – 13

Ultra High Frequency (UHF)Range 470 – 806 MHzChannels 14 - 69

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Cellular Phones

Use microwave frequenciesRequires a network of towers for signals

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Communication Satellites

Spacecraft that orbit EarthReceive and send messages to ground

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Satellite Phone

Never out of rangeVery expensive requires many orbiting

satellites

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Satellite Television

Distributes AM and FM signals to entire EarthSmall dish used to collect signals from spaceSignals are often scramble to prevent theft

Must buy descrambler to get image (box)

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GPS

Global Positioning SystemSatellites orbit at same speed as Earth turns

Therefore can give exact location on EarthUse several satellites together for accuracy

Used by military initiallyNow available in most new cars

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Review

• Illuminated vs luminous• Different Types of light bulbs

– Incandescent– Fluorescent– Vapor– Neon

• AM vs FM• Satellites

Quiz

Homework

Chose one type of light bulb and describe how it works. List at least one advantage of this type of light bulb.