How the Sun Works

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How Capacitors Work

In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitorsand batteries both store electrical energy. If you have read How Batteries Work, then you know that a

battery has two terminals. Inside the battery, chemical reactions produce electronson one terminal and

absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new

electrons it only stores them.

In this article, we'll learn e!actly what a capacitor is, what it does and how it's used in electronics. We'll

also look at the history of the capacitor and how several people helped shape its progress.

Inside the capacitor, the terminals connect to two metal platesseparated by a non-conducting

substance,or dielectric. "ou can easily make a capacitor from two pieces of aluminumfoil and a piece

of paper. It won't be a particularly good capacitor in terms of its storage capacity, but it will work.

In theory, the dielectric can be any nonconductive substance. However, for practical applications, specific

materials are used that best suit the capacitor's function. #ica, ceramic, cellulose, porcelain, #ylar,

$eflonand evenairare some of the nonconductive materials used. $he dielectric dictates what kind of

capacitor it is and for what it is best suited. %epending on the si&e and type of dielectric, some capacitors

are better for high freuency uses, while some are better for high voltage applications. (apacitors can be

manufactured to serve any purpose, from the smallest plastic capacitor in your calculator, to an ultra

capacitor that can power a commuter bus. )A*Auses glass capacitors to help wake up the space

shuttle's circuitry and help deploy space probes. Here are some of the various types of capacitors and

how they are used.

Air +ften used in radio tuning circuits

#ylar #ost commonly used for timer circuits like clocks, alarms and counters

lass ood for high voltage applications

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(eramic -sed for high freuency purposes like antennas,rayand#/Imachines

Capacitor Circuit

In an electronic circuit, a capacitor is shown like this0

When you connect a capacitor to a battery, here's what happens0

$he plate on the capacitor that attaches to the negative terminal of the battery

accepts electronsthat the battery is producing.

$he plate on the capacitor that attaches to the positive terminal of the battery loses electrons to

the battery.

+nce it's charged, the capacitor has the same voltageas the battery 12.3 volts on the battery means 2.3

volts on the capacitor4. 5or a small capacitor, the capacity is small. But large capacitors can hold uite abit of charge. "ou can find capacitors as big as soda cans that hold enough charge to light aflashlight

bulbfor a minute or more.

6ven nature shows the capacitor at work in the form of lightning. +ne plate is thecloud,the other plate is

the ground and the lightningis the charge releasing between these two 7plates.7 +bviously, in a capacitor

that large, you can hold a huge amount of charge8

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9et's say you hook up a capacitor like this0

Here you have a battery, a light bulband a capacitor. If the capacitor is pretty big, what you will notice is

that, when you connect the battery, the light bulb will light up as current flows from the batteryto the

capacitor to charge it up. $he bulb will get progressively dimmer and finally go out once the capacitor

reaches its capacity. If you then remove the battery and replace it with a wire, current will flow from one

plate of the capacitor to the other. $he bulb will light initially and then dim as the capacitor discharges,

until it is completely out.

In the ne!t section, we'll learn more about capacitance and take a detailed look at the different ways that

capacitors are used.

LIKE A WATER TWER

+ne way to visuali&e the action of a capacitor is to imagine it as a water towerhooked to a pipe. A water

tower 7stores7 water pressure when the water system pumps produce more water than a town needs,

the e!cess is stored in the water tower. $hen, at times of high demand, the e!cess water flows out of the

tower to keep the pressure up. A capacitor stores electron in the same way and can then release them

later.

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!arad

A capacitor's storage potential, or capacitance, is measured in units called "arads. A 2farad capacitor

can store one coulomb 1coolomb4 of charge at 2 volt. A coulomb is :.;3e2< 1:.;3 = 2>?2> = ;.< 2>,> farads to hold it, because an amphour is ,:>> ampseconds.

If it takes something the si&e of a can of tuna to hold a farad, then 2>,> farads is going to take up a 9+$

more space than a single AA battery8 +bviously, it's impractical to use capacitors to store any significant

amount of power unless you do it at a high voltage.

Applications

$he difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny

fraction of a second, where a battery would take minutes to completely discharge. $hat's why the

electronic flash on a camerauses a capacitor the battery charges up the flash's capacitor over several

seconds, and then the capacitor dumps the full charge into the flash tube almost instantly. $his can make

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a large, charged capacitor e!tremely dangerous flash units and $Cshave warnings about opening them

up for this reason. $hey contain big capacitors that can, potentially, kill you with the charge they contain.

(apacitors are used in several different ways in electronic circuits0

*ometimes, capacitors are used to store charge for highspeed use. $hat's what a flash does.Big lasersuse this techniue as well to get very bright, instantaneous flashes.

(apacitors can also eliminate ripples. If a line carrying %( voltage has ripples or spikes in it, a big

capacitor can even out the voltage by absorbing the peaks and f illing in the valleys.

A capacitor can block %( voltage. If you hook a small capacitor to a battery, then no current will

flow between the poles of the battery once the capacitor charges. However, any alternating

current 1A(4 signal flows through a capacitor unimpeded. $hat's because the capacitor will

charge and discharge as the alternating current fluctuates, making it appear that the alternating

current is flowing.

In the ne!t section, we'll look at the history of the capacitor and how some of the most brilliant minds

contributed to its progress.

History o" t$e Capacitor

$he invention of the capacitor varies somewhat depending on who you ask. $here are records that

indicate a erman scientist named 6wald eorg von Dleist invented the capacitor in )ovember 2E@3.

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*everal months later Fieter van #usschenbroek, a %utch professor at the -niversity of 9eyden came up

with a very similar device in the form of the Leyden %ar, which is typically credited as the first capacitor.

*ince Dleist didn't have detailed records and notes, nor the notoriety of his %utch counterpart, he's often

overlooked as a contributor to the capacitor's evolution. However, over the years, both have been given

eual credit as it was established that their research was independent of each other and merely a

scientific coincidence

$he 9eyden Gar was a very simple device. It consisted of a glass Gar, half filled with water and lined inside

and out with metal foil. $he glass acted as the dielectric, although it was thought for a time that water was

the key ingredient. $here was usually a metal wire or chain driven through a corkin the top of the Gar. $he

chain was then hooked to something that would deliver a charge, most likely a handcranked static

generator. +nce delivered, the Gar would hold two eual but opposite charges in euilibrium until they

were connected with a wire, producing a slight spark or shock

BenGamin 5ranklin worked with the 9eyden Gar in his e!periments with electricity and soon found that a flat

piece of glass worked as well as the Gar model, prompting him to develop the "lat capacitor, or 5ranklin

suare. "ears later, 6nglish chemist #ichael 5araday would pioneer the first practical applications for the

capacitor in trying to store unused electronsfrom his e!periments. $his led to the first usable capacitor,

made from largeoilbarrels. 5araday's progress with capacitors is what eventually enabled us to deliver

electric power over great distances. As a result of 5araday's achievements in the field of electricity, the

unit of measurement for capacitors, or capacitance, became known as the farad .

How Inductors Work

An inductor is about as simple as an electronic component can get it is simply a coil of wire. It turns out,

however, that a coil of wire can do some very interesting things because of the magnetic properties of a

coil.

In this article, we'll learn all about inductors and what they're used for.

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Inductor &asics

In a circuit diagram, an inductor is shown like this0

$o understand how an inductor can work in a circuit, this figure is helpful0

What you see here is a battery, alight bulb,a coil of wire around a piece of iron1yellow4 and a switch.

$he coil of wire is an inductor. If you have read How 6lectromagnets Work, you might recogni&e that the

inductor is an electromagnet.

If you were to take the inductor out of this circuit, what you would have is a normal flashlight. "ou close

the switch and the bulb lights up. With the inductor in the circuit as shown, the behavior is completely

different.

$he light bulb is a resistor1the resistance creates heat to make the filament in the bulb glow see How

9ight Bulbs Workfor details4. $he wire in the coil has much lower resistance 1it's Gust wire4, so what youwould e!pect when you turn on the switch is for the bulb to glow very dimly. #ost of the current should

follow the lowresistance path through the loop. What happens instead is that when you close the switch,

the bulb burns brightly and then gets dimmer. When you open the switch, the bulb burns very brightly and

then uickly goes out.

$he reason for this strange behavior is the inductor. When current first starts flowing in the coil, the coil

wants to build up a #agnetic "ield. While the field is building, the coil inhibits the flow of current. +nce

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the field is built, current can flow normally through the wire. When the switch gets opened, the magnetic

field around the coil keeps current flowing in the coil until the field collapses. $his current keeps the bulb

lit for a period of time even though the switch is open. In other words, an inductor can store energyin its

magnetic field, and an inductor tends to resist any change in the amount of current flowing through it.

THI'K A&(T WATER)))

+ne way to visuali&e the action of an inductor is to imagine a narrow channel with water flowing through

it, and a heavy water wheel that has its paddles dipping into the channel. Imagine that the water in the

channel is not flowing initially.

)ow you try to start the water flowing. $he paddle wheel will tend to prevent the water from flowing until it

has come up to speed with the water. If you then try to stop the flow of water in the channel, the spinning

water wheel will try to keep the water moving until its speed of rotation slows back down to the speed of

the water. An inductor is doing the same thing with the flow of electrons in a wire an inductor resists a

c$ange in t$e "low o" electrons.

Henries

$he capacityof an inductor is controlled by four factors0

$he number of coils #ore coils means more inductance.

$he material that the coils are wrapped around 1the core4

$he crosssectional area of the coil #ore area means more inductance.

$he length of the coil A short coil means narrower 1or overlapping4 coils, which means more

inductance.

Futting ironin the core of an inductor gives it much more inductance than air or any nonmagnetic core

would.

$he standard unit of inductance is the Henry. $he euation for calculating the number of henries in an

inductor is0

H * + .i /Turns /Turns coil Area #u0 1 +coil Lengt$ 23,333,3330

$he area and length of the coil are in meters. $he term #uis the per#eabilityof the core. Air has a

permeability of 2, while steel might have a permeability of ;,>>>.

Inductor Application4 Tra""ic Lig$t 5ensors

9et's say you take a coil of wire perhaps : feet 1; meters4 in diameter, containing five or si! loops of wire.

"ou cut some grooves in a road and place the coil in the grooves. "ou attach an inductance meter to the

coil and see what the inductance of the coil is.

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)ow you park a car over the coil and check the inductance again. $he inductance will be much larger

because of the large steel obGect positioned in the loop's magnetic field. $he car parked over the coil is

acting like the core of the inductor, and its presence changes the inductance of the coil. #ost traffic light

sensorsuse the loopin this way. $he sensor constantly tests the inductance of the loop in the road, and

when the inductance rises it knows there is a car waiting8

How Lig$t E#itting 6iodes Work

Lig$t e#itting diodes, commonly called 96%s, are real unsung heroes in the electronics world. $hey dodo&ens of different Gobs and are found in all kinds of devices. Among other things, they form numbers

on digital clocks, transmit information fromremote controls,light up watches and tell you when your

appliances are turned on. (ollected together, they can form images on aGumbo television

screenorilluminate a traffic light.

Basically, 96%s are Gust tiny light bulbs that f it easily into an electrical circuit. But unlike

ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get especially

hot. $hey are illuminated solely by the movement of electrons in asemiconductormaterial, and they last

Gust as long as a standard transistor. $he lifespan of an 96% surpasses the short life of an incandescent

bulb by thousands of hours. $iny 96%s are already replacing the tubes that light up9(%H%$Cs to make

dramatically thinner televisions.

In this article, we'll e!amine the technology behind these ubiuitous blinkers, illuminating some cool

principles of electricity and light in the process.

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At t$e %unction, "ree electrons "ro# t$e '-type #aterial "ill $oles "ro# t$e .-type #aterial) T$is

creates an insulating layer in t$e #iddle o" t$e diode called t$e depletion 7one)

W$at is a 6iode8

W$en t$e negati9e end o" t$e circuit is $ooked up to t$e '-type layer and t$e positi9e end is

$ooked up to .-type layer, electrons and $oles start #o9ing and t$e depletion 7one disappears)

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W$en t$e positi9e end o" t$e circuit is $ooked up to t$e '-type layer and t$e negati9e end is

$ooked up to t$e .-type layer, "ree electrons collect on one end o" t$e diode and $oles collect on

t$e ot$er) T$e depletion 7one gets bigger)

A diode is the simplest sort of semiconductordevice. Broadly speaking, a semiconductor is a material with

a varying ability to conduct electrical current. #ost semiconductors are made of a poor conductor that has

had impurities 1atomsof another material4 added to it. $he process of adding impurities is called doping.

In the case of 96%s, the conductor material is typically aluminumgalliumarsenide 1AlaAs4. In pure

aluminumgalliumarsenide, all of the atoms bond perfectly to their neighbors, leaving no free electrons

1negatively charged particles4 to conduct electric current. In doped material, additional atoms change thebalance, either adding free electrons or creating holes where electrons can go. 6ither of these alterations

make the material more conductive.

A semiconductor with e!tra electrons is called )type material, since it has e!tra negatively charged

particles. In )type material, free electrons move from a negatively charged area to a positively charged

area.

A semiconductor with e!tra holes is called Ftype material, since it effectively has e!tra positively charged

particles. 6lectrons can Gump from hole to hole, moving from a negatively charged area to a positively

charged area. As a result, the holes themselves appear to move from a positively charged area to a

negatively charged area.

A diode consists of a section of )type material bonded to a section of Ftype material, with electrodes on

each end. $his arrangement conducts electricity in only one direction. When no voltage is applied to the

diode, electrons from the )type material fill holes from the Ftype material along the Gunction between the

layers, forming a depletion &one. In a depletion &one, the semiconductor material is returned to its original

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insulating state all of the holes are filled, so there are no free electrons or empty spaces for electrons,

and charge can't flow.

$o get rid of the depletion &one, you have to get electrons moving from the )type area to the Ftype area

and holes moving in the reverse direction. $o do this, you connect the )type side of the diode to the

negative end of a circuit and the Ftype side to the positive end. $he free electrons in the )type materialare repelled by the negative electrode and drawn to the positive electrode. $he holes in the Ftype

material move the other way. When the voltage difference between the electrodes is high enough, the

electrons in the depletion &one are boosted out of their holes and begin moving freely again. $he

depletion &one disappears, and charge moves across the diode.

If you try to run current the other way, with the Ftype side connected to the negative end of the circuit

and the )type side connected to the positive end, current will not flow. $he negative electrons in the )

type material are attracted to the positive electrode. $he positive holes in the Ftype material are attracted

to the negative electrode. )o current flows across the Gunction because the holes and the electrons are

each moving in the wrong direction. $he depletion &one increases. 1*ee How *emiconductors Workfor

more information on the entire process.4

$he interaction between electrons and holes in this setup has an interesting side effect it generates

light8 In the ne!t section, we'll find out e!actly why this is.

How Can a 6iode .roduce Lig$t8

9ightis a form of energy that can be released by an atom. It is made up of many small particlelike

packets that have energy and momentum but no mass. $hese particles, called photons, are the most

basic units of light.

Fhotons are released as a result of moving electrons. In an atom, electrons move in orbitals around the

nucleus. 6lectrons in different orbitals have different amounts of energy. enerally speaking, electrons

with greater energy move in orbitals farther away from the nucleus.

5or an electron to Gump from a lower orbital to a higher orbital, something has to boost its energy level.

(onversely, an electron releases energy when it drops from a higher orbital to a lower one. $his energy is

released in the form of a photon. A greater energy drop releases a higherenergy photon, which is

characteri&ed by a higher freuency. 1(heck out How 9ight Worksfor a full e!planation.4

As we saw in the last section, free electrons moving across a diode can fall into empty holes from the F

type layer. $his involves a drop from the conduction band to a lower orbital, so the electrons releaseenergy in the form of photons. $his happens in any diode, but you can only see the photons when the

diode is composed of certain material. $he atoms in a standard silicon diode, for e!ample, are arranged in

such a way that the electron drops a relatively short distance. As a result, the photon's freuency is so low

that it is invisible to thehuman eye it is in the infrared portion of the light spectrum. $his isn't necessarily

a bad thing, of course0 Infrared 96%s are ideal for remote controls, among other things.

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Cisible lightemitting diodes 1C96%s4, such as the ones that light up numbers in adigital clock,are made

of materials characteri&ed by a wider gap between the conduction band and the lower orbitals. $he si&e of

the gap determines the freuency of the photon in other words, it determines the color of the light.

While 96%s are used in everything from remote controls to the digital displays on electronics, visible

96%s are growing in popularity and use thanks to their long lifetimes and miniature si&e. %epending on

the materials used in 96%s, they can be built to shine in infrared, ultraviolet, and all the colors of the

visible spectrum in between.

In the ne!t section we'll look at the advantages of 96%s.

T$e interior o" a LE6 is actually :uite si#ple, w$ic$ is one o" t$e reasons t$is tec$nology is so

9ersatile)

LE6 Ad9antages

While all diodes release light, most don't do it very effectively. In an ordinary diode, the semiconductor

material itself ends up absorbing a lot of the light

energy. 96%s are specially constructed to release a large number of photons outward. Additionally, they

are housed in a plastic bulb that concentrates the light in a particular direction. As you can see in the

diagram, most of the light from the diode bounces off the sides of the bulb, traveling on through the

rounded end.

96%s have several advantages over conventional incandescent lamps. 5or one thing, they don't have a

filament that will burn out, so they last much longer. Additionally, their small plastic bulb makes them a lot

more durable. $hey also fit more easily into modernelectronic circuits.

But the main advantage is e""iciency. In conventional incandescent bulbs, the lightproduction process

involves generating a lot of heat 1the filament must be warmed4. $his is completely wasted energy, unless

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you're using the lamp as a heater, because a huge portion of the available electricity isn't going toward

producing visible light. 96%s generate very little heat, relatively speaking. A much higher percentage of

the electrical power is going directly to generating light, which cuts down on the electricity demands

considerably.

Ferwatt, 96%s output more lumens of light than regular incandescent bulbs. 9ight emitting diodes have ahigher lu#inous e""icacy1how efficiently electricity is converted to visible light4 than incandescents for

e!ample, *ewell's 6vo9u! 96% bulb produces E:. lumens per watt compared to an incandescent bulb's

2E lmJW Ksource0 *ewellL. And they last0 96%s can have lifetimes of ;3,333 $ours or

#oreKsource0%esign /ecycle IncL.

-p until recently, 96%s were too e!pensive to use for most lighting applications because they're built

around advanced semiconductor material. $he price of semiconductor devices has plummeted since the

year ;>>>, however, making 96%s a more costeffective lighting option for a wide range of situations.

While they may be more e!pensive than incandescent lights up front, their lower cost in the long run can

make them a better buy. *everal companies have begun selling 96% light bulbs designed to compete with

incandescent and compact fluorescents that promise to deliver long lives of bright light and ama&ing

energy efficiency.

+ver the ne!t couple of pages we'll take a look at the future of 96%s in our homes. +ne day they may be

plugged into our light bulb sockets, lighting up our digital readouts and illuminating the millions of pi!els

that make up our highdefinition televisions.

LE6 Lig$t &ulbs 9s) Incan descents and !luorescents

5or decades, 2>>watt incandescent light bulbshave lit up hallways and bedroomsM :>watt

incandescents have shone softer light from reading lamps and closets. But incandescent lights have

some problems. $hey're inefficient, wasting lots of energy as heat, and have shorter lifespans than

fluorescent lamps. /ecently, compact fluorescent 1(594bulbs have become popular alternatives to

incandescent bulbs thanks to lower power consumption. Where incandescent lights last an average of

around 2,>>> hours, (59s can last >> hours. -nfortunately, C!Ls contain towatt incandescent light bulb draws

more than N>> worth of electricity per year and provides about > lumens of lightM an euivalent

compact fluorescent uses less than 23 watts and costs only about NE3 of electricity per year. 96% bulbs

are even better, drawing less than < watts of power, costing about N> per year, and lasting 3>,>>> hours

or longer Ksource0%esign /ecyle IncL. $here are only hours in a whole year imagine how long an

96% bulb would last in the average home8

$hat makes 96%s sound pretty great and they are but there's a reason incandescent and compact

fluorescent bulbs are still around. 96% bulbs present a high upfront cost compared to other bulbs.

Incandescent bulbs sell in packages for only a few bucks. As of mid;>22, *ewell's 6vo9u! 96% bulbs

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sold for more than NE> apiece8 However, because of their longer life spans and dramatically lower power

usage, 96% bulbs make up for the high barrier of entry. *ince there's no to!ic mercury in an 96%, they're

also easier and cheaper to dispose of than (59s. And since 96%s can be built to light up in a variety of

colors, they don't need filters like other bulbs.

96% lighting obviously isn't perfect yet. In addition to the high cost barrier, 96%s are vulnerable to hightemperatures. If 96% circuitry gets too hot, more current will pass through the%unctionmentioned earlier

in this article. When too much current courses through the Gunction, it will cause irreversible burnout often

called LE6 #eltdown.

96%s and fluorescents put off 7cool7 or bluish light compared to the 7warm,7 yellowish light typical of

incandescent bulbs. $he difference in lighting types can take some adGustment, but 96%s obviously offer

numerous advantages over incandescents. 96%s are even easy to dim and are perfect for encouraging

plant growth, since they efficiently put off tons of light without producing heat that could potentially be

damaging to plant life.

LE6 T=s and t$e !uture o" Lig$t E#itting 6iodes

96%s have come a long way since the early days of lighting up digital clock faces. In the ;>>>s,9(%$Cs

took over the high definition market and represented a huge step over old standard definition (/$

televisions. 9(% displays were even a maGor step above H% rearproGection sets that weighed well over

2>> pounds 1 @3.@ kilos4. )ow 96%s are poised to make a similar Gump. While 9(%s are far thinner and

lighter than massive rearproGection sets, they still use cold cathode fluorescent tubes to proGect a white

light onto the pi!els that make up the screen. $hose add weight and thickness to the television set. 96%s

solve both problems.

Have you ever seen a a gigantic flatscreen $C barely an inch thickO If you have, you've seen an 96%

television. Here's where the acronyms get a bit confusing0 those 96% $Cs are still 9(% $Cs, because the

screens themselves are comprised of liuid crystals. $echnically, they're LE6-backlit9(% $Cs. Instead of

fluorescent tubes, 96%s shine light from behind the screen, illuminating the pi!els to create an image.

%ue to the small si&e and low power consumption of 96%s, 96%backlit $Cs are far thinner than regular

9(% sets and are also more energy efficient. $hey can also provide a wider color gamut, producing more

vivid pictures.

Because 96% $Cs are still in their infancy, several different types of 96%blacklit sets are on the market

and not all 96% $Cs are created eual. #any sets use white LE6 edge lig$tingto shine light across the

display. $he only real advantage afforded by these sets is thinness. R>& LE6-backlit sets, on the other

hand, provide improved color. *ome configurations even allow for a techniue called local di##ing,

where 96%s in different parts of the display can be brightened or dimmed independently to create a more

dynamic picture Ksource0 96% $eleL. And that highlights one more great advantage of 96%s over compact

fluorescent lights0 Because the 96%s can actually be instantly toggled on and off, they produce awesome

black levels in dark scenes. *ince the white fluorescent lamps have to remain on during $C use, some

light tends to bleed through and lighten the picture in dark scenes.

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In the future, some of the most incredible uses of 96%s will actually come fromorganic light emitting

diodes,or LE6s. $he organic materials used to create these semiconductors are fle!ible, allowing

scientists to create bendable lights and displays. *omeday, +96%s will pave the way for the ne!t

generation of $Cs and smart phones can you imagine rolling your $C up like a poster and carrying it

with you anywhereO

How 5e#iconductors Work

*emiconductors have had a monumental impact on our society. "ou find semiconductors at the heart

of microprocessor chipsas well as transistors. Anything that's computeri&ed or uses radio wavesdepends

on semiconductors.

$oday, most semiconductor chips and transistors are created with silicon. "ou may have heard

e!pressions like 7*ilicon Calley7 and the 7silicon economy,7 and that's why silicon is the heart of any

electronic device.

A diodeis the simplest possible semiconductor device, and is therefore an e!cellent beginning point if

you want to understand how semiconductors work. In this article, you'll learn what a semiconductor is,

how doping works and how a diode can be created using semiconductors. But first, let's take a close look

at silicon.

*ilicon is a very common element for e!ample, it is the main element in sand and uart&. If you look

7silicon7 up in the periodic table,you will find that it sits ne!t to aluminum, below carbon and abovegermanium.

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5ilicon sits ne

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6oping 5ilicon

"ou can change the behavior of silicon and turn it into a conductor by dopingit. In doping, you mi! a

small amount of an i#purityinto the silicon crystal.

$here are two types of impurities0

'-type In )type doping ,phosphorusor arsenicis added to the silicon in small uantities. Fhosphorus

and arsenic each have five outer electrons, so they're out of place when they get into the silicon lattice.

$he fifth electron has nothing to bond to, so it's free to move around. It takes only a very small uantity of

the impurity to create enough free electrons to allow an electric current to flow through the silicon. )type

silicon is a good conductor. 6lectrons have a negative charge, hence the name )type.

.-type In Ftype doping, boronor galliumis the dopant. Boron and gallium each have only three outer

electrons. When mi!ed into the silicon lattice, they form 7holes7 in the lattice where a silicon electron has

nothing to bond to. $he absence of an electron creates the effect of a positive charge, hence the name F

type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over

a space. Ftype silicon is a good conductor.

A minute amount of either )type or Ftype doping turns a silicon crystal from a good insulator into a

viable 1but not great4 conductor hence the name 7semiconductor.7

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)type and Ftype silicon are not that ama&ing by themselvesM but when you put them together, you get

some very interesting behavior at the Gunction. $hat's what happens in a diode.

A diodeis the simplest possible semiconductor device. A diode allows current to flow in one direction but

not the other. "ou may have seen turnstiles at a stadium or a subway station that let people go through in

only one direction. A diode is a oneway turnstile for electrons.

When you put )type and Ftype silicon together as shown in this diagram, you get a very interesting

phenomenon that gives a diode its uniue properties.

6ven though )type silicon by itself is a conductor, and Ftype silicon by itself is also a conductor, the

combination shown in the diagram does not conduct any electricity. $he negative electrons in the )type

silicon get attracted to the positive terminal of the battery. $he positive holes in the Ftype silicon get

attracted to the negative terminal of the battery. )o current flows across the Gunction because the holes

and the electrons are each moving in the wrong direction.

If you "lip t$e battery around, the diode conducts electricity Gust fine. $he free electrons in the )type

silicon are repelled by the negative terminal of the battery. $he holes in the Ftype silicon are repelled by

the positive terminal. At the%unctionbetween the )type and Ftype silicon, holes and free electrons

meet. $he electrons fill the holes. $hose holes and free electrons cease to e!ist, and new holes and

electrons spring up to take their place. $he effect is that current "lowsthrough the Gunction.

In the ne!t section we'll look at the uses for diodes and transistors.

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6iodes and Transistors

A device that blocks current in one direction while letting current flow in another direction is called a

diode. %iodes can be used in a number of ways. 5or e!ample, a device that uses batteries often contains

a diode that protects the device if you insert the batteries backward. $he diode simply blocks any current

from leaving the battery if it is reversed this protects the sensitive electronics in the device.

A semiconductor diode's behavior is not perfect, as shown in this graph0

When re9erse-biased, an ideal diode would block all current. A real diode lets perhaps 2> micro amps

through not a lot, but still not perfect. And if you apply enough reversevoltage1C4, the Gunction breaks

down and lets current through. -sually, the breakdown voltage is a lot more voltage than the circuit willever see, so it is irrelevant.

When "orward-biased, there is a small amount of voltage necessary to get the diode going. In silicon,

this voltage is about >.E volts. $his voltage is needed to start the holeelectron combination process at the

Gunction.

Another monumental technology that's related to the diode is the transistor. $ransistors and diodes have a

lot in common.

Transistors

A transistoris created by using t$ree layersrather than the two layers used in a diode. "ou can create

either an )F) or a F)F sandwich. A transistor can act as a switch or an amplifier.

A transistor looks like two diodes backtoback. "ou'd imagine that no current could flow through a

transistor because backtoback diodes would block current both ways. And this is true. However, when

you apply a small current to the center layerof the sandwich, a much larger current can flow through the

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sandwich as a whole. $his gives a transistor its switc$ingbehavior. A small current can turn a larger

current on and off.

A silicon c$ipis a piece of silicon that can hold thousands of transistors. With transistors acting as

switches, you can create Boolean gates,and with Boolean gates you can create microprocessor chips.

$he natural progression from silicon to doped silicon to transistors to chips is what has made

microprocessors and other electronic devices so ine!pensive and ubiuitous in today's society. $he

fundamental principles are surprisingly simple. $he miracle is the constant refinement of those principles

to the point where, today, tens of millions of transistors can be ine!pensively formed onto a single chip.

How Webca#s Work

If you have been e!ploring the Webfor any length of time, then you have run across any number

of Webca#sin your travels. Webcams range from the silly to the serious a Webcam might point at a

coffee or a space shuttlelaunch pad. $here are business cams, personal cams, private cams, traffic

cams... "ou name it and there's probably a Webcam pointed at it.

Have you ever considered setting up a Webcam yourselfO "ou might want to create a funny Webcam by

pointing it at your hamster or putting it inside your refrigerator. But it turns out there are lots of productiveuses for Webcams, too. 5or e!ample0

"ou will be out of town for a week and you want to keep an eye on your house.

"ou'd like to be able to check on the baby sitter and make sure everything is +D while you are at

work.

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"ou'd like to know what your dog does in the back yard all day.

"ou want to let the grandparents watch the new baby during nap time.

If there is something that you would like to monitor remotely, a Webcam makes it easy.

In this article, we will look at the steps you can take to put up your own simple Web camera.

T$e &asic Idea

Webcams, like most things, range from simple to comple!. If you understand the essence of a simple

Webcam setup, increasing the comple!ity is only a matter of adding functionality through software,

custom code andJor euipment connections.

A simple Webcam setup consists of a digital ca#eraattached to your co#puter,typically through

the -*B port.$he camera part of the Webcam setup is Gust a digital camera there's really nothing

special going on there. $he 7Webcam7 nature of the camera comes with the software. Webcam software

7grabs a frame7 from the digital camera at a preset interval 1for e!ample, the software might grab a still

image from the camera once every > seconds4 and transfers it to another location for viewing. If you're

interested in using your Webcam for streaming video, you'll want a Webcam system with a high "ra#e

rate. 5rame rate indicates the number of pictures the software can grab and transfer in one second. 5or

streaming video, you need a minimum rate of at least 23 frames per second 1fps4, and > fps is ideal. $o

achieve high frame rates, you need a highspeedInternetconnection.

+nce it captures a frame, the software broadcasts the image over your Internet connection. $here are

several broadcast methods. -sing the most common method, the software turns that image into a PF6

fileand uploads it to a Web serverusing 5ile $ransfer Frotocol 15$F4. "ou can easily place a PF6 image

on any Web page1for information on creating Web pages and adding PF6 images, see How WebFages Work4.

If you don't have your own Web server, lots of companies offer you a free place to upload your images,

saving you the trouble of having to set up and maintain a Web server or a hosted Web site.

W$at ?ou 'eed

In order to create a simple Webcam, you need three things0

A ca#eraof some sort connected to your computer

A piece of so"twarethat can grab a frame from the camera periodically

A way to broadcast your i#ages on t$e Web

If you have your own Web ser9erand Web site, you already have a way to post your Webcam images on

the Web. At its most basic, a Web serveris simply a piece of hardware that has the ability to deliver Web

based content to a Web browser. 5or some people, their home computer serves as their Web server. If

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that's the case, a camera, a piece of software and your F(are all that you need. If you want to use a Web

server that's hosted elsewhere 1for e!ample, if you're paying anA*Fto host your Web server4, you also

need0

$he ability to #o9e "ra#esfrom your computer to the Web server, typically by !ile Trans"er

.rotocol15$F4. 5or most Web servers, this is no problemM but occasionally, a hosting companywill have policiesin place that make this difficult.

A relatively consistent connectionbetween your computer and the Internet.

Amodemconnection to an I*Fis fine if it is something that you keep connected most of the time,

which implies that you have a dedicatedphone linefor your computer. If you have something like

acable modemthat is connected all the time, that's perfect.

If you don't have a Web server or a Web site, and you don't want one, you can simply have someone else

maintain your Webcam images. 9ots of Webcam software comes complete with Webbased image

access. $hey usually offer different access options, including remote access, which utili&es -%F

protocolto transfer your Webcam images directly from your computer to another computer. $his can be

done0

via Web browser, in which case the software itself establishes its own H$$Fserver so anyone

using a Web browser can access the Webcam images on your F(

via traditional 5$Fupload to a remote Web server

By using this type of service, you avoid having to host andJor maintain your own Web site. If you are using

one of these services and you want the image to refresh itself constantly, you need a relatively consistent

connection between your computer and the Internet. If your connection is not consistent, it won't hurt

anything. It Gust means that the image won't always be up to date.

5etting It (p

In order to e!periment with Webcams and go through the process of setting one up, got itself a Webcam.

$o set it up, here is what we did0

2. We went down to the local computer warehouse and bought the Intel Fro Cideo F( (amera.

;. We installed the software for the camera on a Windows F machine.

. We went to the Web site www.webcam;.comand downloaded a program called Webca#@.$his is a popular software package for Webcams. "ou can get a free demo version or pay N.3

for the full version. We went ahead and paid for a registered copy. 1$he complete user's manual

for this product is available on the Web site. (heck it out to see the wide array of features

available on today's Webcam software.4

@. We installed Webcam;. It was a very easy installation.

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3. After entering the address of the 5$F site and a couple of other pieces of information, the

Webcam showed its first signs of life8

:. We pointed the camera out the window.

E. We then tuned the software a bit to reduce the file si&e of the images and to enablethe te#porary-"ile copyingfeature.

$here are many different features you can e!periment with in Webcam;0 streaming video, chat,

captions, ACI files and different resolutionsand compression ratios, to name a few. Webcam; also

supports the Auto(am feature, which allows you to create a Web page for your Webcam for free on the

company's server. $he software makes it simple.

As you can see, setting up a basic Webcam is e!tremely easy. If nothing else, the setup described here is

a fun, ine!pensive and simple way to e!periment with a Webcam and see what you can do with one of

your own8

Ad9anced !eatures

+nce you manage the simple system, you can look into other Webcam features and settings like0

Botion sensing $he Webcam takes a new picture when it detects motion.

I#age arc$i9ing "ou can create an archive that saves all of your Webcam images or only

certain images at preset intervals.

=ideo #essaging *ome instant messenger programs support Webcam video.

Ad9anced connections -se wired or wireless methods to connect yourhometheaterAJC

euipment to your Webcam.

Auto#ation /obotic cameras let you set a series of panJtilt positions and program frame

capture settings based on the position of the camera.

5trea#ing #edia 5or professional applications, a Webcam setup can use #F6@

compression to achieve true streaming audio and video 1this is the compression system used in

most of the popular F(based media players4.

Custo# coding Import your own computer code to tell the Webcam what to do.

+ne e!ample of custom coding is a set of commands that makes a Webcam image auto#atically

re"res$. $he simple Webcam system we've set up in this article produces a static image. -sers have to

refresh the image manually 1by pushing the /efresh button in the browser4 if they want to see any

changes. $here are three different techniues you can use to create automatic refreshing0

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"ou can add a #eta tagto the H$#9for the page so that the page refreshes at some freuency.

$he tag to add is0 #eta $ttp-e:ui9*Dre"res$D content*D@3D$he 7>7 is the number of

seconds between each refresh and can be set to anything you like. $he entire page will reload

every > seconds, so it is beneficial to keep the page short.

"ou can add a Fa9a appletto your site. $he Webcam; and Pava Appletspage e!plains how toobtain and install the free applet. $he applet is a program that automatically fetches the image

periodically. $he advantage is that only t$e i#age re"res$es, not the entire page. #ost browsers

support Pava applets, so most of your viewers will have no problem.

"ou can use Fa9a5cript, as demonstrated on $he Pava*cript *ource0 /efresh1look at the source

code onthis page4. "ou can also check out How Pava Worksfor a detailed look at Pava

programming.

Webca# 'etworking

+ne problem with using a camera hooked to a computer via a -*Bcable is the li#ited cable lengt$.What if the room you want to capture is at the other end of the house, or outsideO In that case, you need

to purchase a camera with e!ternal connections. "ou have a few options0

"ou can place a standard camera anywhere in the house and run a video cable with /(A Gacks

on it from the camera to the computer. $here are all sorts of places on the Web that sell

small pinhole video cameras,either on their own or embedded in things like clocks and smoke

detectors. "ou can f ind small security cameras for less than N2>>. avoid the cable by using

aradio, an 6thernetconnection or aWi5isetup. If you already have ahome network,

connecting an e!ternal Webcam to your computer probably won't reuire any additional

networking.

#onitoring your home and sharing images via the Web are only a couple of the things you can do with

your Webcam. $here are any number of ways to make use of a camera that's connected to your

computer. "ou can get software that will let you make video phone callswith a friend who also has a

Webcam. "ou can hold a videoconferencing session with business associates on the other side of the

world. "ou can conduct a video interview and broadcast it live on yourblog.*ome Webcam software will

even deliver images directly to your WebenabledF%Aorsmartphone.+ther products let you connect

your camcorder to your Webcam setup so you can let everybody watch your vacation footage via the

Internet. $he possibilities are endless.

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