Electricity and Electronics - PolleyTechnical.com...particles of an atom. Atoms are the building blocks ofall things. The universe and everything initiscomposed ofatoms. Composition

Electricity andElectronicsOBJECTIVES.. describe the relationships

among voltage, current, andresistance.

.. explain the basic organizationof the two mai n types ofcircuits.

.. describe the operation and usesof diodes and transistors.explain the operation of anelectronic or electrical device interms of input, process, andoutput.

KEY TERMSbatterycircuitcurrentelectricityelectromagnetismgeneratorOhm's lawpotential differenceresistancetransistor

Imagine that you lived 200 years ago. Youwouldhave been living in a world without electricity .Consider the ways in which your life would havebeen different.Many people might argue that harnessing

electrical energy has been the most significanttechnological event of all time. Our technologiesuse thousands of devices that rely on electricity andelectronics.This chapter will help you understand the nature

of electricity as an energy source. It will also helpyou see how we use electricity and electronics tocontrol technology.

288 SEC T ION 6 Control Technologies

WHAT IS ELECTRICITY?The study of electricity can be difficult.

One reason why is that we usually can'tsee electricity. We know it's there becausewe can see the results of its work. We feelthe heat from a blow dryer and watch thepaddles on the ceiling fan turn-but whatis electricity?Electricity is the flow of electrons

through a pathway that conductselectricity-a wire, for example. Electrons,as will be explained, are tiny chargedparticles of an atom. Atoms are thebuilding blocks of all things. The universeand everything in it is composed of atoms.

Composition of MatterMatter is anything that occupies space

and has mass. Matter is made up of atoms.Matter may take the form of a solid, aliquid, or a gas. It may be an element, acompound, or a mixture.

FASCINATING FACTSThe Greek word elektron is the source ofthe word electricity. In Greek, electronmeans amber. Amber is the hardenedresin of pine trees that grew millionsof years ago. When amber is rubbed,it can attract objects. One of the firstknown examples of static electricitywas observed by the ancient Greeks.They noticed that rubbing amber causedit to attract objects.

An element is the purest form of matter.An element is made up of atoms. An atom isthe smallest particle of an element thatretains the properties of that element. Forexample, salt can be broken down intosodium and chlorine. Elements are so purethat they cannot be broken down anyfurther. There are about 105 knownelements. Every substance on Earth is madeof one or more of these elements. Fig. 15-1.

Aluminum foil

Aluminum --Element13 --__,!_ Atomic number

AI-symbOl

26.982 ----,- Atomic weight

• Fig. 15·1 Thesmallest part of anelement that still behaveslike that element is anatom. Assume that youwere able to cut a piece ofaluminum foil into smallerand smaller pieces. Thesmallest particle that stillbehaved like aluminumwould be a singlealuminum atom.

CHAPTER 15 Electricity and Electronics 289

There are over 100 elements. Each onehas a unique atomic structure. Everysubstance on Earth is made up of one ormore of these elements.Many times, two or more different

atoms combine to form molecules.Molecules combine to form compounds.Compounds are matter composed ofchemically combined atoms of two ormore elements. Mixtures are also acombination of two or more elements.However, these elements are notchemically combined. They retain theirown properties. The periodic table ofelements lists known elements .

Atomic StructureAn atom has two parts: a center portion,

or nucleus, and a cloud of electrons thatsurrounds the nucleus. Tightly packedwithin the nucleus are particles calledprotons (PRO-tahns) and neutrons (NEW-trahns). Fig. 15-2.The number of neutrons in an atom is

always equal to or greater than thenumber of protons (except for hydrogen).Atoms of the same element may vary inthe number of neutrons. Such atoms arecalled isotopes (I-so-topes) .

• ~ig. 15·2 A nucleus in the center of the atom consists of closely packed proton and neutronparticles. A cloud of electrons surrounds the nucleus.


A neutral atom has one electron foreach proton in the nucleus. An atom canlose or gain electrons, however. Thisprocess, which upsets the balance ofneutrality, is called ionization (I-on-uh-zay-shun). It is very important to the flowof electricity.

Energy Levels and Electrons

Electrons move about at various energylevels at different distances from thenucleus. The area in which the electronsmove is known as the electron cloud. Theenergy levels of the atom are oftenreferred to as shells. The innermostelectrons are at the lowest energy level.Those of the outermost shell are at thehighest energy level. The outermost shellis called the valence (VAY-lence)shell.Electrons in the outermost subshell of

the valence shell are called valenceelectrons. Valence electrons are moreloosely bound to the atom than innerelectrons. Since valence electrons havemore energy and are more loosely bound,they can escape from the atom whenenough external energy is absorbed. The

escaped valence electron is called a freeelectron.

Atomic Charges

Protons and electrons in atoms containtiny amounts of electrical energy, orcharges. Protons have a positive charge,while electrons have a negative charge.Neutrons are neutral. They have noelectrical charge.When ionization occurs, the neutral

atom loses or gains an electron andbecomes an ion (I-on). When a neutralatom loses an electron, the atom becomesa positive ion because it has more protonsthan electrons. When a neutral atom gainsan electron, the atom becomes negativelycharged, or becomes a negative ion.Similar to the poles on a magnet, like

charged particles tend to repel each other.Unlike charged particles attract eachother. This phenomenon is known as thelaw of charges. Fig. 15-3. Atoms seek themost stable level possible. It is theinteraction between charged particles thatcauses the flow of electrons that we callelectricity.

• Fig. 15·3 When charged particles come close to each other, a force is produced. This force can beeither a force of attraction or repulsion.

Unlike charges attract.

+ )))))

ccccc- CCCCC

))))) -Like charges repel. --------....j~


Voltage, Current, andResistanceA charge has stored energy with the

potential to do work. For example, thepotential energy at the negative terminalof a battery differs from that at thepositive terminal. In a complete electricpath, this difference in potential causes acharge to move through the circuit. Thispotential difference, as it is called, is theforce that causes electrons to flow.

A potential difference is also referred toas a voltage, or electromotive force (emf).Voltage is an excess of electrons stored inone location and waiting to move.Some materials are made of atoms that

do not have a strong hold on valenceelectrons. These materials are calledconductors. Metals are generally goodconductors. Copper, aluminum, silver, andgold, for example, are excellentconductors. Fig. 15-4.When voltage is applied to a conductor,

the excess electrons of the negative end ofthe wire travel to the positive end, or theend with too few electrons.The flow of electrons in a wire or other

conductor is known as current. Currentcontinues until the charges at both ends ofthe conductor are equal. Figure 15-5shows how current flows through aconductor.

Fig. 15·4 Metals are good conductors ofelectricity. Materials that conduct electricity haveelectrons that are not held tightly in place. Theseelectrons are free to move.

In contrast to conductors, somematerials are made of atoms that have atight hold on electrons and a few freeelectrons. Those materials that resist theflow of voltage are called insulators.Plastic and ceramic materials are goodinsulators. However, if enough voltage isapplied, electrons can be forced fromatom to atom through the insulator.Insulators have different strengths. Thestrength of an insulator represents itsresistance.

Copper wire with free electrons- •Electron added Electron forced off• +

Electron flow

• Fig. 15·5 The way in which current flows through a conductor.

CHAPTER 15 Electricitl' and Electronics 293

Linking to SCIENCEExploring Positive and Negative

Charges. Objects with the same chargerepel each other. Those with differentcharges attract each other. You canobserve this through a simpleexperiment. Obtain two balloons. Blowup one balloon, knot the end, and rub iton a wool sweater. You will be able tomake the balloon stick (temporarily) tothe classroom wall. The balloon has anegative charge and the wall has apositive charge. Now, blow up a secondballoon and knot the end. Cut two 1-footlengths of thread. Suspend each balloonfrom a thread by taping or tying. Rub theballoons on a wool sweater to give thema negative charge. Holding them by thethread ends, bring them close enough totouch. You'll see that they quickly moveapart. Why?

Resistance is the opposition to the flowof electrons. Different substances havedifferent resistances. Conductors have lowresistance. Insulators have very highresistance.

SOURCES OFELECTRICITYAs mentioned, for electrons to flow,

there must be a potential difference, orvoltage. The source that supplies thisvoltage is called a voltage source. It can beproduced from a variety of differentprimary energy sources. These primarysources take energy in one form andconvert it to electrical energy. Two voltagesources-batteries and generators-arediscussed here.


--- - ~~---------

Cells and BatteriesHave you ever wondered how a battery

works? A battery is a device that convertschemical energy into electrical energy. Abattery generates electrical energy(voltage) with a chemical reaction.The batteries used in flashlights are also

called "cells." A cell is a device made oftwo different conducting materials in aconducting solution. The conductors arecalled electrodes (e-LEC-trodes). Theconducting solution is called an electrolyte(e-LEC-tro-light) .Dry cells have a paste electrolyte of

powdered chemicals. A flashlight batteryis a common dry cell. Wet cells contain aliquid electrolyte. A car battery is a wetcell. Fig. 15-6.

_~_Plasticinsulator

Ammonium~- .....:---chloride paste

f-----t..,_- Carbon rod

Zinc container

Fig. 15·6 Batteries change chemical energyinto electrical energy. Voltage is created throughchemical reaction. In a carbon zinc ceLL,electronstravel from the zinc to the carbon rod.

A chemical reaction occurs in the cellbetween the two electrodes. Theelectrolyte positively charges oneelectrode and negatively charges theother. In this way, the cell producesvoltage.When connected to a conductor, cells

and batteries produce a current that flowsin only one direction. This current is calleddirect current (dc).

GeneratorsMechanical energy is the energy of

motion. A generator is a device thatchanges mechanical energy into electricalenergy. A generator uses electromagneticinduction to force electrons from theiratoms. Early scientists found that theycould produce an electric current bymoving a wire through a magnetic field.When a wire cuts across the invisible linesof force of the magnetic field, voltage isinduced in the wire. In addition, if thewire forms a complete circuit, a current isinduced as well. Fig. 15-7.Generators vary in type and in

construction. A simple generator is madeup of a coil of wire wrapped around ametal core and placed between the polesof a magnet. The wire coil and coreassembly is called an armature (ARM-uh-chur). This can rotate. As the armaturerotates, the coil cuts across the magneticfield. Consequently, voltage is induced inthe coil.Each half-turn, the two connections at

the output of the generator changepolarity. First one end is positive and theother end is negative, then vice versa. Thecurrent by such a voltage changes

Coil ,

'I8'Is§

is'

Battery

Switch

Paper Clips

• Fig. 15·7 An electromagnet can be made bywinding fine insulated copper wire around an ironnail and connecting this device to a battery. Anelectromagnet can produce a stronger magneticfield than the field produced by a permanentmagnet. An electromagnetic can also be turned onand off.

direction each time the polarity changes.This electricity is known as alternatingcurrent (ac).Most of the electricity we use is

alternating current generated in powerplants that use large generators.Mechanical energy is used to turn therotating parts of these huge machines.This energy comes from turbines. Theseare bladed wheels that turn when struckby the force of steam or moving water. Asthe shaft turns, the armature rotates. Thisgenerates electrical energy, or voltage.


Table is·A. Voltage, Current, and Resistance

Electrical energy depends on three factors: voltage, current, and resistance. Therelationship of these three factors determines the amount of electrical energyproduced.

Physical Quantity Symbol Measure of Unit of MeasureVoltage VorE Force Volts (V)Current 1 Electron Flow Amperes (A)

Resistance R Opposition to Flow Ohms (Q)

ElectromagnetsIf electricity can be induced by cutting

across magnetic lines of force, canmagnetism be induced from electricity?The answer is yes. An electric currentflowing through a wire creates a magneticfield around the wire. The relationshipbetween electricity and magnetism iscalled electromagnetism.Electromagnets are powerful magnets

created by wrapping wire around an ironcore and then passing electric currentthrough the wire. The magnetic field canbe controlled by turning the current on andoff. The strength of the magnetic field canbe increased in two ways. It can beincreased by increasing the number of coilswrapped around the core and by increasingthe current flowing through the coil.

RELATIONSHIPS AMONGVOLTAGE, CURRENT, ANDRESISTANCEYou have learned that the force used to

move electrons is called voltage. Voltage isa measurable quantity. The unit ofmeasure for voltage is the volt. The symbolfor volts is V, though E is sometimes used.

296 5 EC T ION 6 Control Technologies

Youhave also learned that current is theterm used to describe the movement ofelectrons in a wire. Current is measured bycounting how many electrons move past acertain point within a wire each second.The symbol for current is I. The unit ofmeasure for current is the ampere, or amp.The symbol for amperes is A.Finally, you have learned that resistance

is the opposition to the flow of electrons.The symbol for resistance is R. The unit ofmeasure for resistance is the ohm. Thesymbol for the ohm is the Greek letter Q(omega).

Ohm's LawWhen voltage is applied to a conductor,

the current that moves through theconductor is directly proportional to theapplied voltage. This relationship isknown as Ohm's law. This law is basic toall studies of electricity. Table IS-A. Ohm'slaw is stated mathematically by theformula:

Current = Voltage/Resistanceor

1= E/R

Linking to MATHEMATICSFinding Resistance. Assume that a

lightbulb uses O.8A of current whenoperating in a 120-V circuit. Using Ohm'slaw, find the resistance of this lightbulb.

ELECTRICAL CIRCUITSIn electricity, a circuit (SIR-cut) is the

pathway through which electrons travel. Asimple circuit consists of a power source, aconductor, and a load. Fig. 15-8. A circuitthat uses direct current as a power sourcemight use a battery or a photovoltaic (foe-tow-vole-TAY-ik) cell. This is also knownas a solar cell. The source of voltage foralternating current is usually a generatorat the power plant.Conductors provide a low-resistance

path from the source to the load. Typically,copper or aluminum wires serve asconductors.The load is the device that uses the

electric energy. The load could be a motor,a buzzer, or a light. The load converts theelectrical energy in the circuit into heat,light, mechanical, or other energy forms.

Main Types of CircuitsThe main types of circuits are series

circuits and parallel circuits.

Series Circuits

When the components are connectedone after another, the circuit is called aseries circuit. In a series circuit, there is

CHAPTER 15

• Fig. 15·8 An eLectricaL circuit is thepathway that eLectricity foLLows. ALLcircuits have aconductor, a Load, and a power source.

Motor

Light

Buzzer

Battery I==tillSolar Cell

Generator

LOAD

CONDUCTOR

POWERSOURCE

Electricity and Etectronics 297

only one pathway for electrons to follow.Fig. 15-9. A break in any part of the circuitstops all the electrons from flowing. Thisproduces an open circuit. Electrons canflow only in a closed circuit.Two rules apply to series circuits:

• The current is the same at all points.• The total resistance of the circuit isequal to the sum of the individualresistance values.

.Parallel Circuits

In a parallel circuit the components arearranged in separate branches. Fig. 15-10.This arrangement provides multiplepathways in which electrons can flow. Abreak in one branch of the circuit does notprevent electrons from flowing in the

other branches. Two rules apply toparallel circuits:• All branches are of equal voltage.• Total current is equal to the sum of thebranch currents.

Complex CircuitsA complex circuit uses switches or other

electronic parts to control the flow ofelectrons from the source to the load.Switches, resistors, and circuit-protectiondevices are used in complex circuits.Switches are used to open and close the

circuit. Different types of switches openand close the circuit in different ways.Resistors are devices that apply

resistance to the flow of electrons in thecircuit.

SERIES CIRCUIT

Direction of electron flow

+ - + II

• Fig. 15·9 A series circuit supplies only one path for the flow of electrons. If that path is brokenat any point, the flow of electrons will stop.


PARALLEL CIRCUIT

+ - +

tt•

• Fig. 15·10 A parallel circuit has many paths along which electrons can flow. A break in one pathwill not stop the flow of electrons in the other paths.

Potentiometers (puh-TEN-she-om-mutters)and Rheostats (REE-uh-stats) are adjustableresistors' that can set a range of desiredresistances. Potentiometers are used to varyvoltage. Rheostats are used to vary current.A dimmer switch on a lamp is an adjustableresistor. The volume control on a radio isanother example.A complex circuit should also contain a

circuit-protection device, such as a fuse or

a circuit breaker. These devices protect thecircuit from large amounts of current. Fig.15-10.Afuse will open a circuit when its rated

current is exceeded. The fuse contains anelement, a thin strip of metal, that meltsat a specified current. When too muchcurrent runs through the fuse, the elementwill melt. The circuit will then open. Fig.lS-11A.


Fig. 15·11 Fuses(A) and circuit breakers (8) prevent the damage that can be caused by excessivecurrent.

A circuit breaker controls a circuit in thesame way as a fuse. However, it uses aprocess that does not require the meltingof the fuse element. One advantage of acircuit breaker is that it can be reset andreused after the problem in the circuit hasbeen fixed. Fig. IS-lIB.

WHAT IS ELECTRONICS?Electronics is the study of precisely

controlling the flow of electrons. Fig. 1S-12. Electronics is the outgrowth of ourknowledge and development of electricalenergy. Electricity and electronics are notthe same.There are key differences between

electricity and electronics. Remember thatelectronics controls the flow of electrons.Electricity controls voltage levels and theflow of current.

300 5 E C T ION 6 Control Technologies

Fig. 15·12 In electronics, the flow ofelectricity is controlled by various devices. Forexample, resistors are placed in a circuit to reducethe flow of electricity. Fuses guard againstdamage. Transistors control the flow of current.

Linking to COMMUNICATIONResearching Power Blackouts. Using

the media center of your school,research the New York blackout of 1968.Determine the cause and length of theoutage and the immediate and long-termeffects. Write a one-page essaypresenting the details of the powerfailure.

SemiconductorsThe precise control of electrons began

with the invention of the vacuum tube. In1948, however, the Bell TelephoneCompany invented the transistor. Atransistor is a semiconductor device thatamplifies and acts as an electronic switch.The transistor is tiny and uses very littleenergy. Transistors rapidly replacedvacuum tubes in electronics. Scientistsbegan using transistors to solve problemsin mathematics. That led to thedevelopment of today's computers.Semiconductors are materials with

properties that fall between insulators andconductors. They conduct better thaninsulators, but not as well as conductors.Silicon and germanium are commonsemiconductor elements. A process calleddoping adds impurities to the puresemiconductor element. This increases itsconductivity. Arsenic and gallium are twoelements commonly added as impurities.Some impurities add extra electrons

that are free to move about the crystal.This produces an n-type semiconductor.Other impurities take away electrons. Thisproduces a p-type semiconductor. Unfilledvalence (VAY-Ience) shells result, leaving

positive sites in the semiconductor crystal.These positive sites are called holes.The holes have a strong attraction for

electrons. Valence electrons from nearbyatoms can "fall" into the hole, leavinganother hole where it had been.Movement of electrons from one hole tothe next makes the holes appear to movein the opposite direction. Conductionthrough the p-type semiconductor is byholes. Conduction through the n-typesemiconductor is by electrons.

Junction DiodesWhen a semiconductor crystal is half n-

type and half p-type, a pn junction isformed between the two regions. Figure15-13 shows a pn junction device knownas ajunction diode. The n-region has manyconduction electrons. The p-region hasmany holes.Because of this junction, electrons can

flow through the semiconductor in onlyone direction, from n-type to p-type.The primary use of a junction diode is to

rectify current, or to change ac into dc.Computers or televisions would notoperate practically with batteries.Therefore, diodes are wired into theircircuits to rectify the current. In this way,such devices can be supplied with directcurrent from a source of alternatingcurrent.

Uses and Types ofTransistorsTransistors have two main uses. They

are used to boost or amplify electronicsignals. They also act as electronic


• Fig. 15·13 Blockdiagram of a junctiondiode. Its schematicsymbol is shown below.Electrons can flow in onlyone direction, from then-region to the p-region. +

o Holes- Electrons(±) Positive ions8Negative ions

switches. For example, they are used toamplify signals in microphones, radios,televisions, and hearing aids. They areused as switches in computers.There are two basic types of transistors:

npn ana pnp. Both have three layers ofsemiconductor materials: a thin centersection, called a base, and two thickerouter layers. One layer is called an emitter.The other layer is called a collector. Wire

npn Block diagram

Base

n

p

Emitter

n Collector

-tl7')" CollectorBase ~

Emitter

n{JnSchematiC symbol

p

/. pn .Junction

• +0 000 • + - - - -000 ;>:< + - - -• +000 0;>:<~ - - -;>:<~000 ><>ic - - ->=c~o 0 0 0 • + - - -

• + -:- Depletion region

Electron flow

+ -.1Schematic symbol

leads are joined to each of these layers.Fig. 15-14.The pn junction is basic to the operation

of transistors as well as diodes. Aforward-bias voltage (negative of source connectedto the n-region of an npn, positive ofsource connected to the p-region) isapplied to the base-to-emitter leads. Atthe same time, a reverse-bias voltage isapplied across the collector-to-emitter

pnp Block diagram

Base

p

n

Emitter

p Collector

-tl7')" CollectorBase ~

Emitterpnp

Schematic symbol

Fig. 15·14 Block diagrams and schematic symbols for npn and pnp bipolar junction transistors.


leads. Current then flows across theforward-biased, emitter-base junction intothe base region. The flow of currentcarriers into the emitter allows current toflow from collector to emitter.Increasing the base current slightly by

increasing the forward-bias voltage causesa much larger collector-to-emitter current.This principle makes the transistor usefulas an amplifier. A small input current cancontrol a much larger output current.In computers, transistors are used to

create logic gates. Logic gates open andclose like electronic switches. They controlthe flow of electrons at lightning speeds.Computers operate on the binary numbersystem. This means that they use Is and Osto represent numbers and characters. Inthe "on" state, the transistor represents thedigit 1. The "off" state represents the digito. Computers process information byadding, subtracting, multiplying, anddividing the binary Is and Os.

ELECTRONIC SYSTEMSElectronic systems are devices that work

together to control, monitor, and measurechanges. Towork, electronic systems musthave inputs, processes, and outputs.The input can be a sensor that converts

a command into an electrical signal. Theinput to your oven is your setting of theoven at a certain temperature.The process is the action that

accomplishes a result. For example, in astreetlight control circuit, a photoresistorenergizes a relay that switches on thestreetlight.The output is the result of the process.

For example, when the battery in yoursmoke detector is low, it may begin to flash.

IMPACTSSystems powered by electronics and

electricity impact all areas of modern life.Such systems have provided many of thetools we need to earn a living. They havealso increased our options forentertainment and travel. The positiveimpacts of electricity have far outweighedany negative impacts. Fig. 15-15.

THE FUTUREElectrical engineers face the challenge

of increasing the power of a device whilelimiting its size. This pattern has beenpresent in the development of the radio,the television, the computer, and thecellular phone. Can you think of others?

Fig.iS-iS The full range of invention isshown by the electrical and electronic devicesused in a large city.


Electronics

ELECTRONICSTECHNICIAN

ELECTRONICDRAFTER

ELECTRICAL ANDELECTRONIC ENGINEER

Electronics manufacturingfinn needs drafter toprepare detailed drawingsand blueprints forelectronic equipment.Draw wiring diagrams,circuit board assemblydiagrams, schematics, andlayout drawings. Sendresume and list ofreferences to: TechnicalElectronics, Inc., P.O.Box7022, Chicago, IL 60032.

Growing developer of aerospace,automotive and military-embeddedcontrol products is in need ofengineers to perform digital andanalog electronic circuit design andreal-time software programming.Bachelor's degree in electricalengineering required. Please sendresume to: P.O. Box 361665, Monroe,MI 65389, or E-mail [email protected].

We are a premier printing companyexpanding our Akron facility andseeking an electronics technician.Responsible for assisting in the design,fabrication, troubleshooting andmaintenance of our electrical/electronicmanufacturing equipment. Computerprogramming and problem-solvingskills necessary. Interested candidatesshould forward a resume to: HumanResources, Sealtight Company, 1978Main Akron Road, Akron, OH 65230.COMPUTER SERVICE

TECHNICIAN

The ideal candidate will have theability to test, troubleshoot, andresolve hardware problems on personalcomputers. Effective customer skillsneeded. Prefer one or two years offormal training in electronics withknowledge of computers. Will workwithout supervision. Submit yourresume to: General Credit InsuranceCompany, 3201 Beachwood Parkway,Orlando, FL 33238.

COMPUTER SALES REPRESENTATIVEComputer retail company has grown to include corporate salesdivision. Challenging opportunity for self-motivated individual tosolicit new business while managing existing accounts. Preferone year of sales experience and PC proficiency. Must havestrong organizational, customer service and communicationskills. We offer competitive compensation package. Send or faxresume to: American Computer Corporation, 24295 BeechwoodAvenue, Cleveland, OH 62240. Fax: (614) 888-3200.

Linking to the WORKPLACEAdvances in technology and

n:an~facturing have impacted our livesLIst fIve electronic products developed inthe past ten years that have affected the

workplace. How did these productschange the ways in which jobs wereperformed?

306 SECTION 6 Control Technologies

mailto:[email protected].

Chapter 15 Review

SUM MAR Y ------------

A battery creates voltage by means of a chemical reaction. A generatorcreates voltage by means of electromagnetic induction.

• When a voltage is applied to a conductor, the current that moves throughthe conductor is directly proportional to the applied voltage. Thisrelationship is known as Ohm's law.In a series circuit, components are connected one after another. In a parallelcircuit, components are arranged in separate branches.A diode allows current to flow through a circuit in only one direction.A transistor controls a large output current with a small input current orvoltage.

CHECK YOUR FACTS

1. Draw and label the parts of an atom.Identify the charges of particle.

2. What force causes electrons to flow?

3. Why are the electrons in the outer shellof the atom more likely to flow thanelectrons in the inner shells?

4. Describe two common sources ofelectromotive force.

5. Explain how Ohm's law describes therelationship among voltage, current, andresistance.

6. How did the invention of transistorsaffect the development of electronics?

7. Identify and describe the organizationof the two main types of circuits.

8. Describe the operation and uses ofdiodes.

9. What design feature do all electronicsystems have in common?

10. Describe the operation and uses oftransistors.

CRITICAL THINKING

1. Describe how a toaster works in terms ofinput, process, and output.

2. Superconductors are materials that havevery low resistance to electron flow. Toachieve this, these materials are subjectedto very low temperatures. What effect doyou think low temperatures might haveon electron flow and resistance? Explainyour answer.

3. Describe how you would design anelectronic fan that turns on when thetemperature reaches 88°F.

4. Describe how doping changes theresistance of a conductor.


Documents

Electricity and Electronics - PolleyTechnical.com...particles of an atom. Atoms are the building blocks ofall things. The universe and everything initiscomposed ofatoms. Composition