1 Unit Two: Voltage, Current, and Resistance John Elberfeld [email protected] ET115 DC Electronics.

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Unit Two:Unit Two:Voltage, Current, Voltage, Current, and Resistanceand Resistance

John ElberfeldJohn Elberfeld

[email protected]

WWW.J-Elberfeld.comWWW.J-Elberfeld.com

ET115 DC Electronics

mailto:[email protected]

ScheduleSchedule

Unit Unit Topic Topic Chpt LabsChpt Labs1.1. Quantities, Units, SafetyQuantities, Units, Safety 11 1 + 21 + 22.2. Voltage, Current, ResistanceVoltage, Current, Resistance 22 3 + 163 + 163.3. Ohm’s LawOhm’s Law 33 5 (35)5 (35)4.4. Energy and PowerEnergy and Power 33 6 (41)6 (41)

5.5. Series CircuitsSeries Circuits Exam IExam I 44 7 (49)7 (49)

6.6. Parallel CircuitsParallel Circuits 55 9 (65)9 (65)

7.7. Series-Parallel CircuitsSeries-Parallel Circuits 66 10 (75)10 (75)

8.8. Thevenin’s, Power Thevenin’s, Power Exam 2Exam 2 66 19 (133)19 (133)

9.9. Superposition Theorem Superposition Theorem 66 11 (81)11 (81)

10.10. Magnetism & Magnetic DevicesMagnetism & Magnetic Devices 77 Lab Final Lab Final 11.11. Course Review and Course Review and Final ExamFinal Exam

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Unit Two Objectives - IUnit Two Objectives - I• Describe the basic structure of an atom Describe the basic structure of an atom

based on the Bohr model.based on the Bohr model.• Define neutron, proton, electron, atomic Define neutron, proton, electron, atomic

number, and shell.number, and shell.• Describe energy levels and valence Describe energy levels and valence

electrons.electrons.• Explain the difference between electron Explain the difference between electron

flow and conventional current.flow and conventional current.• Explain how conductors, semiconductors, Explain how conductors, semiconductors,

and insulators differ from an atomic and insulators differ from an atomic viewpoint.viewpoint.

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Unit Two Objectives - IIUnit Two Objectives - II• Give examples of solids liquids and Give examples of solids liquids and

conductors that are conductors and conductors that are conductors and solids, liquids and gases that are solids, liquids and gases that are insulators.insulators.

• Identify the symbols for resistors, variable Identify the symbols for resistors, variable resistors, voltage sources,switches, fuses, resistors, voltage sources,switches, fuses, circuit breakers, various grounds, and circuit breakers, various grounds, and meters.meters.

• Illustrate how symbols can be connected Illustrate how symbols can be connected to form a schematic.to form a schematic.

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Unit Two Objectives - IIIUnit Two Objectives - III• Describe the elements of a basic circuit.Describe the elements of a basic circuit.• Relate a schematic to a physical circuit.Relate a schematic to a physical circuit.• Define open-circuit and closed circuit.Define open-circuit and closed circuit.• Define ground or common.Define ground or common.• Explain how wire sizes are related to Explain how wire sizes are related to

gauge numbers.gauge numbers.• Define the unit of resistance.Define the unit of resistance.• Describe basic types of resistors.Describe basic types of resistors.• Determine the resistance value of a four- Determine the resistance value of a four-

or five-band resistor from the color code.or five-band resistor from the color code.

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Unit Two Objectives - IVUnit Two Objectives - IV• Given a resistor value and tolerance, list the Given a resistor value and tolerance, list the

color code for a four- or fiveband resistor.color code for a four- or fiveband resistor.• Use a digital multimeter (DMM) to measure Use a digital multimeter (DMM) to measure

a predetermined low voltage on a power a predetermined low voltage on a power supply.supply.

• Measure resistances and voltages in a DC Measure resistances and voltages in a DC circuit using a DMM.circuit using a DMM.

• Explain the Multisim workbench and show Explain the Multisim workbench and show how to construct a basic circuit.how to construct a basic circuit.

• Test circuits by connecting simulated Test circuits by connecting simulated instruments in Multisim.instruments in Multisim.

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Reading AssignmentReading Assignment• Read and study Read and study

• Chapter 2: Voltage, Current, Chapter 2: Voltage, Current, and Resistance Pages 21-61and Resistance Pages 21-61

• Handout: “Conventional Current Handout: “Conventional Current versus Electron Flow”versus Electron Flow”

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Lab AssignmentLab Assignment

• Lab Experiment 16: All of itLab Experiment 16: All of itResistance - Page 119-122Resistance - Page 119-122

• Lab Experiment 3:Lab Experiment 3:

• Page 25 #3-6Page 25 #3-6

• Page 26 #3-6Page 26 #3-6

• Rip out pages 23-26, 199-122 staple Rip out pages 23-26, 199-122 staple them together SEPARATELY, put them together SEPARATELY, put youryour NAME NAME on the pages, and turn on the pages, and turn them in before you leave the labthem in before you leave the lab

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Written AssignmentsWritten Assignments• Answer the questions on the Answer the questions on the

handout.handout.

• Be prepared for a quiz on questions Be prepared for a quiz on questions similar to those on the homework.similar to those on the homework.

• If there are any calculations, you If there are any calculations, you must show ALL your work for credit:must show ALL your work for credit:– Write down the formulaWrite down the formula– Show numbers in the formulaShow numbers in the formula– Circle answer with the proper unitsCircle answer with the proper units

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Electrical ChargesElectrical Charges• People have seen the effects of People have seen the effects of

electricity for thousands of yearselectricity for thousands of years– Lightning, electric shocks, static clingLightning, electric shocks, static cling

• Only two types of electric Only two types of electric charges exist: charges exist: positive ( + ) and positive ( + ) and negative ( - )negative ( - )

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Static ElectricityStatic Electricity

• Early scientists described electrical Early scientists described electrical chargescharges– Like charged objects repel each otherLike charged objects repel each other– Unlike charged objects attract each Unlike charged objects attract each

otherother

– Early scientists had no idea why it Early scientists had no idea why it worked or what caused itworked or what caused it

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ElectricityElectricity

• We now know that electric current is We now know that electric current is the flow of the flow of electronselectrons

• To understand electricity, you need a To understand electricity, you need a solid understanding of matter and solid understanding of matter and how electrons behave in different how electrons behave in different materialsmaterials

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Atomic Structure – Bohr ModelAtomic Structure – Bohr Model

• Nucleus of an atom Nucleus of an atom is a hard core center is a hard core center containing neutrons containing neutrons and protonsand protons

• A proton carries a A proton carries a positive charge and positive charge and a neutron is a neutron is electrically neutral.electrically neutral.

• Negative electrons Negative electrons orbit the nucleusorbit the nucleus

• Electrons are small Electrons are small and light, and can and light, and can escape from the escape from the atomatom

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Planetary ModelPlanetary Model• Protons are too Protons are too

massive and too bound massive and too bound together to movetogether to move

• Electrons ( - ) orbit the Electrons ( - ) orbit the nucleus in specific nucleus in specific shells (K, L, M…)shells (K, L, M…)

• Number of protons Number of protons equals number of equals number of electrons in a normal electrons in a normal atom – Electric charges atom – Electric charges balancebalance

• Only electrons move Only electrons move away from the atomaway from the atom

+o

+o

+o+

o+

+o

o

Electrons

Nucleus

K

L

IonsIons• An atom that has a net charge other than An atom that has a net charge other than

zero is called an ion.zero is called an ion.

• Normal atoms are NOT ions.Normal atoms are NOT ions.

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Conductors and InsulatorsConductors and Insulators• Current electricity is the movement of Current electricity is the movement of

electronselectrons• Conductors let electrons move easily and Conductors let electrons move easily and

so offer low resistance to current flowso offer low resistance to current flow• Insulators oppose the flow of electrons and Insulators oppose the flow of electrons and

so offer high resistance to current flowso offer high resistance to current flow• Semiconductors offer moderate, Semiconductors offer moderate,

controllable resistancecontrollable resistance• Resistance – the opposition to the flow of Resistance – the opposition to the flow of

current – current – depends on atomic structuredepends on atomic structure

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ConductorsConductors

• In conductors, it is easy to get an In conductors, it is easy to get an electron away from the outer most electron away from the outer most shell (valance band) of an atom and shell (valance band) of an atom and to have the electron carry energy as to have the electron carry energy as it moves through a materialit moves through a material– Motion of electrons makes up electric Motion of electrons makes up electric

current!current!– Electrons carry energy Electrons carry energy

from one place to anotherfrom one place to another+

o+o

+o+

o+

+o

o

-

-

-

-

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ConductorsConductors• Conductors Conductors

contain a large contain a large number of free number of free electrons.electrons.

• Low resistance Low resistance means the means the material is a material is a good electricity good electricity conductorconductor

Lowest Resistance at top

Silver

Copper

Gold

Aluminum

Tungsten

Iron

Nichrome

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InsulatorsInsulators• Insulators Insulators

prevent the flow prevent the flow of electricityof electricity

• A material with A material with high resistance high resistance is a poor is a poor conductor and conductor and good insulator of good insulator of electricityelectricity

Highest Resistance at top

Mica

Glass

Teflon

Paper

Rubber

Bakelite

Oils

Porcelain

Air

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• The metallic bond consists of a series of The metallic bond consists of a series of metals atoms that have all donated their metals atoms that have all donated their valence electrons to an electron cloud that valence electrons to an electron cloud that permeates the structure. permeates the structure.

• This electron cloud is frequently referred to This electron cloud is frequently referred to as an electron sea. as an electron sea.

Metallic bondMetallic bond

Current FlowCurrent Flow

• Some substances such as copper have one Some substances such as copper have one valence electron in their outermost orbitvalence electron in their outermost orbit

• At room temperature they have many free At room temperature they have many free electrons and are good conductorselectrons and are good conductors

• Electron current flow occurs as electrons Electron current flow occurs as electrons move away from the negative terminal move away from the negative terminal towards the positive terminal.towards the positive terminal.

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Analogy for Current FlowAnalogy for Current Flow• For every tennis ball that enters the For every tennis ball that enters the

tube, one ball leaves the tubetube, one ball leaves the tube

• Electric current also acts this wayElectric current also acts this way

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Requirements for Current FlowRequirements for Current Flow

1.1. Electromotive Force (Voltage source)Electromotive Force (Voltage source)

2.2. Complete path for currentComplete path for current

Electron flow

Electrical CircuitsElectrical Circuits• Circuits have a voltage source, a Circuits have a voltage source, a

“load” that makes use of the “load” that makes use of the electricity, a complete circuit of wires electricity, a complete circuit of wires that carry the electrons from (-) to (+) that carry the electrons from (-) to (+) terminals, and often a switchterminals, and often a switch

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Basic Electrical QuantitiesBasic Electrical Quantities• The basic quantities used to describe The basic quantities used to describe

electricity are:electricity are:– Charge (Coulombs)Charge (Coulombs)– Current (Amperes)Current (Amperes)– Voltage (Volts)Voltage (Volts)– Resistance (Ohms)Resistance (Ohms)– Energy (Joules)Energy (Joules)– Power (Watts)Power (Watts)

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ChargesCharges• Electrons have a negative charge Electrons have a negative charge

• Protons have a positive chargeProtons have a positive charge

• The charge on an electron is equal in The charge on an electron is equal in magnitude but opposite in sign to a magnitude but opposite in sign to a protonproton

• The charge on an electron is the The charge on an electron is the smallest unit of electrical charge that smallest unit of electrical charge that exists in natureexists in nature

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Real World MeasurementsReal World Measurements• We usually deal with billions and We usually deal with billions and

billions of electronsbillions of electrons• 1 coulomb = 6.25 x 101 coulomb = 6.25 x 101818 electrons electrons• The charge on a object depends on The charge on a object depends on

how many EXTRA charged particles how many EXTRA charged particles are thereare there– Usually the number of electrons Usually the number of electrons

balances the number of protons, so the balances the number of protons, so the net charge is 0net charge is 0

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ChargesCharges• When an object has a negative charge, When an object has a negative charge,

it has more electrons than protonsit has more electrons than protons– Charge is determined by how many Charge is determined by how many

more electrons it hasmore electrons it has• When an object has a positive charge, it is When an object has a positive charge, it is

missing electrons missing electrons and has more protons and has more protons than electronsthan electrons– Protons do NOT move – only electrons Protons do NOT move – only electrons

move to and from an objectmove to and from an object

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Electric ChargeElectric Charge

• Electric charge has the symbol QElectric charge has the symbol Q

• Electric charge is measured in Electric charge is measured in Coulombs which has C for an Coulombs which has C for an abbreviationabbreviation

• 1 Coulomb = 6.25 x 101 Coulomb = 6.25 x 1018 18 electronselectrons

• For example:For example:

• Q = 4 C = 25 x 10Q = 4 C = 25 x 101818 electrons electrons

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ProblemProblem• Fact: 1 C = 6.25 x 10Fact: 1 C = 6.25 x 101818 electrons electrons

• A capacitor stores a charge of 80 A capacitor stores a charge of 80 μμC. C. How many extra electrons are in the How many extra electrons are in the capacitor?capacitor?

• This is a simple unit conversion This is a simple unit conversion problem using large exponentsproblem using large exponents

• Answer is in Engineering notationAnswer is in Engineering notation

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ExampleExample• Fact: 1 C = 6.25 x 10Fact: 1 C = 6.25 x 101818 electrons electrons

• A capacitor stores a charge of 80 A capacitor stores a charge of 80 μμC. C. How many extra electrons are in the How many extra electrons are in the capacitor?capacitor?

• 80 x 1080 x 10-6-6 C x (6.25 x 10 C x (6.25 x 101818 electrons/C) electrons/C) = 500 x 10= 500 x 101212 electrons electrons

• This is a simple unit conversion This is a simple unit conversion problem using large exponentsproblem using large exponents


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• How many coulombs in 3.0 x 10How many coulombs in 3.0 x 101313 electrons?electrons?

• On homework, you MUST show your On homework, you MUST show your work like that abovework like that above


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• How many coulombs in 3.0 x 10How many coulombs in 3.0 x 101313 electrons?electrons?

• 3.0 x 103.0 x 1013 13 el. x (1C/ 6.25 x 10el. x (1C/ 6.25 x 101818 el. ) = el. ) =

• 4.8 x104.8 x10-6-6 C = 4.8 C = 4.8 μμCC

• On homework, you MUST show your On homework, you MUST show your work like that abovework like that above


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On your ownOn your own

• Fact: 1 C = 6.25 x 10Fact: 1 C = 6.25 x 101818 electrons electrons

• If you have 25.2 x 10If you have 25.2 x 102626 extra extra electrons, what is the charge in electrons, what is the charge in coulombs in engineering notation?coulombs in engineering notation?

• If you have 428 x 10If you have 428 x 10-6-6 coulombs, what coulombs, what number of extra electrons do you number of extra electrons do you have?have?


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• Electric current is:Electric current is:– Movement of electrons from negatively Movement of electrons from negatively

charged regions to positively charged charged regions to positively charged regionsregions

– Represented as Represented as I (the letter “eye”)I (the letter “eye”)

Electric CurrentElectric Current

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Electric CurrentElectric Current• Electric current is the motion of free Electric current is the motion of free

electrons through a material.electrons through a material.

• Current is measured in AmperesCurrent is measured in Amperes

• 1 Ampere of current has 1 coulomb 1 Ampere of current has 1 coulomb of electrons flowing past a given of electrons flowing past a given point in the wire in just 1 secondpoint in the wire in just 1 second

• I = 1 A = 1 C/sI = 1 A = 1 C/s

Current FlowCurrent Flow

• Current flows because batteries or other Current flows because batteries or other devices concentrate electrons in one devices concentrate electrons in one place, creating a minus charge, and move place, creating a minus charge, and move electrons away from another place, electrons away from another place, leaving a positive chargeleaving a positive charge

• Electrons are pushed out of the negative Electrons are pushed out of the negative region and pulled toward the positive region and pulled toward the positive regionregion

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Current SymbolCurrent Symbol• The symbol for current is the letter I.The symbol for current is the letter I.• I = Q/T (Charge in coulombs/seconds)I = Q/T (Charge in coulombs/seconds)

– C is already used for capacitors and coulombs, C is already used for capacitors and coulombs, so I is less confusing for current, and Q for so I is less confusing for current, and Q for chargecharge

• Batteries are a source of electric currentBatteries are a source of electric current• Electrons flow from the negative terminal Electrons flow from the negative terminal

through the wire to the positive terminalthrough the wire to the positive terminal

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Conventional CurrentConventional Current• Before scientist knew about Before scientist knew about

electrons, they guessed that electrons, they guessed that electricity was the flow of positive electricity was the flow of positive particles, but they were particles, but they were wrongwrong

• However, many books and most However, many books and most electrical symbols are drawn to show electrical symbols are drawn to show the direction this positive current the direction this positive current would flow.would flow. Electrons

Conventional Current

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Current CalculationsCurrent Calculations

• Fact: I = Q / tFact: I = Q / t

• What is the current if 75 C pass a What is the current if 75 C pass a point in 1s?point in 1s?

• I = 75 C / 1 s = 75 AI = 75 C / 1 s = 75 A

• What is the current if 10 C pass a What is the current if 10 C pass a point 0.5 sec?point 0.5 sec?

• I = 10 C / 0.5 s = 20 AI = 10 C / 0.5 s = 20 A

103=k10-3 = m10-6 = μ

On your ownOn your own• Determine the current in each of the Determine the current in each of the

following casesfollowing cases

• 5 C in 2 s5 C in 2 s

• Six-tenths coulomb passes a point in Six-tenths coulomb passes a point in 3 s. What is the current in amperes?3 s. What is the current in amperes?

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WorkWork• According the the SCIENTIFIC According the the SCIENTIFIC

definition:definition:

• Work is done when a force moves an Work is done when a force moves an objectobject– Pushing an object that does not move is Pushing an object that does not move is

NOT doing workNOT doing work– An object coasting along with no force An object coasting along with no force

pushing it is NOT doing workpushing it is NOT doing work

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Measuring WorkMeasuring Work• You buy electricity because of its You buy electricity because of its

ability to do work, like turn motorsability to do work, like turn motors

• Work and Energy (the ability to do Work and Energy (the ability to do work) are measured in work) are measured in JoulesJoules..

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Voltage Voltage • When bodies with unequal charges are When bodies with unequal charges are

separated by a distance, there exists a separated by a distance, there exists a force between them and the potential to force between them and the potential to move charges or objects and so do work move charges or objects and so do work

• This potential difference between the This potential difference between the points is known as voltage. points is known as voltage.

• The unit of potential difference orThe unit of potential difference or voltage is Volt. voltage is Volt.

• EMF or Electro Motive Force EMF or Electro Motive Force is the same as Voltageis the same as Voltage

VoltageVoltage

• One volt is the potential required to One volt is the potential required to move one coulomb between two move one coulomb between two points while expending onepoints while expending one joule of energy joule of energy..– 1 V = 1 J/C1 V = 1 J/C

• Voltage gives you an idea of the energy the Voltage gives you an idea of the energy the electrons have, and how much work they electrons have, and how much work they can docan do

• It also indicates the “push” used to move It also indicates the “push” used to move the electrons through the wirethe electrons through the wire– Chemical reactions in batteriesChemical reactions in batteries

supply energy to electrons to supply energy to electrons to give them the potential to dogive them the potential to do work work

CalculationsCalculations• Voltage (V) is energy (W) per unit Voltage (V) is energy (W) per unit

charge (Q)charge (Q)– Energy is the Work (W) that is done and Energy is the Work (W) that is done and

is measured in JOULES (learn this!)is measured in JOULES (learn this!)

• V = W / QV = W / Q• How much energy (W) How much energy (W) in JOULES in JOULES

does a 12 V (V) battery use to move does a 12 V (V) battery use to move 2.5 C (Q) through the electric circuit?2.5 C (Q) through the electric circuit?

• 12 V = W / 2.5 C12 V = W / 2.5 C• W = 12 V x 2.5 C = 30 JW = 12 V x 2.5 C = 30 J

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Creating Voltage DifferencesCreating Voltage Differences

• Voltages exist when electrons want Voltages exist when electrons want to flow from one place to another to flow from one place to another because of an imbalance of electric because of an imbalance of electric charges (One place positive – the charges (One place positive – the other negative)other negative)

• Electrons are usually balanced Electrons are usually balanced perfectly by the protonsperfectly by the protons

• It takes energy to upset this balanceIt takes energy to upset this balance

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Basic Law Of ChargesBasic Law Of Charges• Like Charges and Unlike ChargesLike Charges and Unlike Charges

– Like charges repelLike charges repel– Unlike charges attractUnlike charges attract

• Significance of this is the ability to do Significance of this is the ability to do work if charges are separated work if charges are separated

• Voltage is like Electrical pressureVoltage is like Electrical pressure• Production of electrical potential is done Production of electrical potential is done

in many waysin many ways• Unit of Measure: VoltUnit of Measure: Volt

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Ways To Create Separation Of ChargeWays To Create Separation Of Charge

• Friction: Friction: Static ElectricityStatic Electricity

• Chemical: Chemical: BatteryBattery

• Mechanical Energy:Mechanical Energy: GeneratorGenerator

• Light Energy:Light Energy: PhotocellPhotocell

• Heat Energy:Heat Energy: ThermocoupleThermocouple

• Pressure:Pressure: PiezoPiezo

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FrictionFriction

• Van de Graaff Van de Graaff generators produce generators produce 100s of thousands of 100s of thousands of volts, but low currentvolts, but low current

• Moving rubber belts Moving rubber belts use friction to shake use friction to shake electrons loose, and electrons loose, and then move them to then move them to the globethe globe

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Generate Static Electricity YourselfGenerate Static Electricity Yourself

• Scuff your feet on the carpet in Scuff your feet on the carpet in winter and then touch a door knob or winter and then touch a door knob or the monitor screenthe monitor screen

• The extra electrons built up on your The extra electrons built up on your body flow in a fraction of a second to body flow in a fraction of a second to a new locationa new location

• Friction builds very high Friction builds very high voltages, but not enough voltages, but not enough power to do useful workpower to do useful work

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• Power generators use moving Power generators use moving magnets and changing magnetism to magnets and changing magnetism to generate electricitygenerate electricity– Most common method of producing Most common method of producing

electrical energy.electrical energy.– Generators are powered Generators are powered

by steam from by steam from nuclear power, coal, ornuclear power, coal, or gas and water, wind, gas and water, wind, or gasoline or gasoline or diesel engines.or diesel engines.

Power GeneratorsPower Generators

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GeneratorsGenerators• In a later unit, you will learn more In a later unit, you will learn more

about how moving magnets generate about how moving magnets generate electricityelectricity

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• Direct currentDirect current– Electrons flow in only one direction.Electrons flow in only one direction.

• Alternating currentAlternating current– Electrons flow in one direction, then in Electrons flow in one direction, then in

the opposite direction.the opposite direction.

– The rest of the unit concentrates on The rest of the unit concentrates on DC voltage and current generationDC voltage and current generation

Type of currentType of current

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• Chemical Energy to Chemical Energy to Electric EnergyElectric Energy– Second most popular method of Second most popular method of

producing electrical energy.producing electrical energy.– Single unit is a cellSingle unit is a cell– Many cells can be Many cells can be

connected to form a connected to form a battery.battery.

Chemical EnergyChemical Energy

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Polarity And Reference PointsPolarity And Reference Points

• Batteries separate Batteries separate negative (-) and negative (-) and positive (+) positive (+) chargescharges

• Chemical reactions Chemical reactions in the battery in the battery generate energy generate energy that is used to that is used to move electrons move electrons within the casewithin the case

Positive

Negative

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Nine Volt BatteryNine Volt Battery

• Many cells Many cells are are involvedinvolved

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• SeriesSeries– Series-aiding:Series-aiding:– The current is the same through every The current is the same through every

cellcell

IIT T = I = I11 = I = I22 = I = I33

– Each cell adds more energy to the Each cell adds more energy to the currentcurrent

VVTT = V = V11 + V + V22 + V + V33 (voltage adds)(voltage adds)

Connecting Cells and BatteriesConnecting Cells and Batteries

VV11

VV22

VV33

IITT

Parallel ConnectionsParallel Connections• ParallelParallel

– The voltage is the same The voltage is the same

VVTT = V = V11 = V = V22 = V = V33 (voltage same) (voltage same)– More current is available if neededMore current is available if needed– More cells means more chemicals More cells means more chemicals

available to produce more electronsavailable to produce more electrons

IITT = I = I11 + I + I22 + I + I33 (current adds) (current adds)

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IITT = I = I11 + I + I22 + I + I33

VT

II1 1 I I22 I I33

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Photoelectric DevicesPhotoelectric Devices

• These convert light energy directly These convert light energy directly into electrical energy.into electrical energy.

• The types of semiconductor devices The types of semiconductor devices that are considered as photoelectric that are considered as photoelectric devices are:devices are:– Photovoltaic cellPhotovoltaic cell– Solar cellSolar cell

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• Photovoltaic cells and solarPhotovoltaic cells and solarcells convert light energy cells convert light energy to electric energyto electric energy

• Many cells must be linked to produce a usable voltage and current.Many cells must be linked to produce a usable voltage and current.• Primarily used in satellites and cameras.Primarily used in satellites and cameras.• Cost is high, but is declining.Cost is high, but is declining.

Light Energy to ElectricityLight Energy to Electricity

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• ThermocoupleThermocouple– Two dissimilar wires twisted together.Two dissimilar wires twisted together.– Voltage is directly proportional to Voltage is directly proportional to

amount of heat applied.amount of heat applied.– Used in thermometers.Used in thermometers.– Also called a pyrometer.Also called a pyrometer.

Heat Energy to ElectricityHeat Energy to Electricity

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• Piezoelectric effect.Piezoelectric effect.

• Voltage is small; must be amplified Voltage is small; must be amplified to be useful.to be useful.

• Used in crystal microphones, Used in crystal microphones, phonograph pickups (crystal phonograph pickups (crystal cartridges) and precision oscillators.cartridges) and precision oscillators.

PressurePressure

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Common Sources Of Electrical EnergyCommon Sources Of Electrical Energy

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ResistanceResistance• The opposition to the flow of electric The opposition to the flow of electric

current is call resistancecurrent is call resistance

• Unit of resistance is Ohm and is Unit of resistance is Ohm and is denoted by the Greek letter omega, denoted by the Greek letter omega, Ω. Ω.

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ResistanceResistance• Not every material will conduct Not every material will conduct

electricityelectricity

• Copper and aluminum conduct Copper and aluminum conduct electricity easily and are labeled electricity easily and are labeled conductors and have low resistanceconductors and have low resistance

• Plastic and rubber do not conduct Plastic and rubber do not conduct electricity easily and are labeled electricity easily and are labeled insulators and have high resistanceinsulators and have high resistance

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SemiconductorsSemiconductors• Silicon and Germanium are Silicon and Germanium are

semiconductorssemiconductors– Neither is a good conductor nor a Neither is a good conductor nor a

insulatorinsulator

• Semiconductors are used in diodes Semiconductors are used in diodes and transistors and other solid state and transistors and other solid state electronics componentselectronics components

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SuperconductorsSuperconductors• At very low temperatures some At very low temperatures some

materials conduct electric current materials conduct electric current very easilyvery easily

• Superconductors can conduct large Superconductors can conduct large amounts of current without any amounts of current without any energy drop in the current energy energy drop in the current energy level so have almost zero resistancelevel so have almost zero resistance

WiresWires• We usually assume wires have 0 We usually assume wires have 0

resistance, but for long wires, this is a resistance, but for long wires, this is a bad assumptionbad assumption

• Resistance in a wire depends on what it Resistance in a wire depends on what it is made out of (copper, aluminum, is made out of (copper, aluminum, silver), its total length, and its diameter.silver), its total length, and its diameter.– Longer wires have more resistance than Longer wires have more resistance than

short wiresshort wires– Thin wires have more resistance than fat Thin wires have more resistance than fat

wireswires

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American Wire Gauge (AWG)American Wire Gauge (AWG)

• The size of a wire is given by the AWG The size of a wire is given by the AWG numbernumber

• Big wires for connecting ovens might Big wires for connecting ovens might be a 10 AWGbe a 10 AWG

• Thinner regular wires for house Thinner regular wires for house circuits might be 12 or 14 gauge circuits might be 12 or 14 gauge

• The wires on your circuit board are 22 The wires on your circuit board are 22 gaugegauge

• High AWG gauge means thinner wire High AWG gauge means thinner wire and higher resistanceand higher resistance

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Measuring ResistanceMeasuring Resistance• Resistance is a measure of how Resistance is a measure of how

much a material opposes the flow of much a material opposes the flow of electricity through itelectricity through it

• A material with a resistance of 1 ohm A material with a resistance of 1 ohm requires 1 volt of energy to get 1 requires 1 volt of energy to get 1 coulomb of charge throughcoulomb of charge through it per second it per second

• R = 1 ohm = 1 R = 1 ohm = 1 Ω = 1 V / AΩ = 1 V / A

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Resistance RangesResistance Ranges• Conductors have resistances of a Conductors have resistances of a

few ohms or lessfew ohms or less

• Insulators have resistances in range Insulators have resistances in range of millions of ohms or moreof millions of ohms or more

• There is no absolute insulator or There is no absolute insulator or perfect conductorperfect conductor

• A resistor is used to provide a definite A resistor is used to provide a definite opposition to current flow in a circuit.opposition to current flow in a circuit.

• The value of a fixed resistor cannot be The value of a fixed resistor cannot be changed after it has been manufactured.changed after it has been manufactured.

• The power rating of a resistor specifies the The power rating of a resistor specifies the maximum power in watts that can be safely maximum power in watts that can be safely dissipated without damage to the resistor. dissipated without damage to the resistor.

• Resistors cannot be manufactured to exact Resistors cannot be manufactured to exact values, so they are given a tolerance rating.values, so they are given a tolerance rating.

• Cheaper resistors has a wider range of Cheaper resistors has a wider range of valuesvalues

ResistorsResistors

Classes of Resistor TechnologyClasses of Resistor Technology

• Carbon-compositionCarbon-composition - most common- most common• Film Film - good - good

precisionprecision• WirewoundWirewound - high power - high power• Surface-mount (SMT)Surface-mount (SMT) - smallest - smallest

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ToleranceTolerance• All resistors have some toleranceAll resistors have some tolerance

– No resistor is perfectNo resistor is perfect

• Tolerances are measured in Tolerances are measured in percentages, like 10%, 5% and 1%.percentages, like 10%, 5% and 1%.

• PartPart = = PercentPercentTotal 100Total 100

• For a 5% resistor:For a 5% resistor:

• Variation Variation = = 5 .5 .Total Ohms 100Total Ohms 100

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ExampleExample• What is the permitted range of values for a What is the permitted range of values for a

4.7 k 4.7 k Ω with 5 % tolerance.Ω with 5 % tolerance.• PartPart = = PercentPercent

Total 100Total 100• PartPart = = 5 5 Part = 4.7k Part = 4.7kΩΩ (5/100) (5/100)

4.7k4.7kΩΩ 100 100

• 5% of 4.7 k 5% of 4.7 k Ω = .05 x Ω = .05 x 4.7 k 4.7 k Ω = 235 ΩΩ = 235 Ω• The range of values is:The range of values is:• 4.7 k 4.7 k Ω - 235 Ω to Ω - 235 Ω to 4.7 k 4.7 k Ω + 235 ΩΩ + 235 Ω• 4.47 4.47 k k Ω to 4.94 Ω to 4.94 k k ΩΩ

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A faster approach…A faster approach…

• If the tolerance of a resistor is 5%, If the tolerance of a resistor is 5%, you can combine steps in a you can combine steps in a calculator to find the range of valuescalculator to find the range of values

• Top: R*(1+.05) = R*(1.05) Top: R*(1+.05) = R*(1.05)

• Bottom: R*(1-.05) = R*(0.95) Bottom: R*(1-.05) = R*(0.95)

• This combines finding 5% (5/100 This combines finding 5% (5/100 or .05) of the value and adding (or or .05) of the value and adding (or subtracting) the 5% from the base subtracting) the 5% from the base value of the resistorvalue of the resistor

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Color Coding ResistorsColor Coding Resistors

• The system of representing the value The system of representing the value of a resistor using bands of color on of a resistor using bands of color on the resistor is called color coding of the resistor is called color coding of resistors.resistors.

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Color Code - MemorizeColor Code - MemorizeColor Value Zeros to add Tolerance

Black 0 0

Brown 1 1 1%

Red 2 2 2%

Orange 3 3

Yellow 4 4

Green 5 5

Blue 6 6

Violet 7 7

Gray 8

White 9

Silver -2 10%

Gold -1 5%

None 20%

Electronic Color CodesElectronic Color Codes

• Resistors and other electronic devices use Resistors and other electronic devices use colors instead of written numbers to colors instead of written numbers to indicate valuesindicate values

• Bright Boys Rave Over Young Girls But Bright Boys Rave Over Young Girls But Veto Getting Wed. Veto Getting Wed.

• Bad Beer Rots Our Young Guts But Vodka Bad Beer Rots Our Young Guts But Vodka Goes WellGoes Well

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Other ApproachesOther Approaches

• Black reflects 0 colors, so Black reflects 0 colors, so it equals 0it equals 0

• Brown is close to blackBrown is close to black• The rainbow goes red, The rainbow goes red,

orange, yellow, green, blue, orange, yellow, green, blue, violetviolet

• Gray is close to white, and Gray is close to white, and white reflects everything white reflects everything so it is the highest numberso it is the highest number

• Red is 2Red is 2

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Resistor AppearanceResistor Appearance

• First Band: NumberFirst Band: Number RedRed

• Second Band: NumberSecond Band: Number BlueBlue

• Third Band: Zeros to addThird Band: Zeros to addOrangeOrange

• Fourth Band: ToleranceFourth Band: Tolerance SilverSilver

• 2 6 000 ohm 10 % = 26 k2 6 000 ohm 10 % = 26 kΩΩ

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ExampleExample

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ExamplesExamples• Red Green Orange: GoldRed Green Orange: Gold

• 2 5 000 at 5% = 25 k2 5 000 at 5% = 25 kΩΩ

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ExamplesExamples• Violet Green Brown : SilverViolet Green Brown : Silver

• 7 5 0 at 10% = 750 7 5 0 at 10% = 750 ΩΩ

Small Resistance ValuesSmall Resistance Values• Rather than add zeroes, sometimes Rather than add zeroes, sometimes

you need to subtract zeroesyou need to subtract zeroes

• 5.6 5.6 ΩΩ = Green Blue Gold = Green Blue Gold

• 5 6 x .1 = 5.6 5 6 x .1 = 5.6 ΩΩ

• 0.78 = Violet Grey Silver0.78 = Violet Grey Silver

• 7 8 x .01 = 0.78 7 8 x .01 = 0.78 ΩΩ

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ExamplesExamples• Green Brown Gold: GoldGreen Brown Gold: Gold

• 5 1 0.1 at 5% = 5.1 5 1 0.1 at 5% = 5.1 ΩΩ

PracticePractice#1 #2 Zeroes Tol Value

RedRed RedRed Black Black GoldGold

22 22 00 5%5% 2222 22 22 ΩΩ 5% 5%

VioletViolet Green Green BrownBrown SilverSilver

77 55 11 10%10% 750750

GreenGreen BrownBrown Brown Brown GoldGold

WhiteWhite BrownBrown GoldGold GoldGold

GrayGray RedRed YellowYellow SilverSilver

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Record your answers on page 26 in the lab manual, #4

Numbers to ColorsNumbers to Colors• Convert the resistance to a regular Convert the resistance to a regular

decimal number with no powers of decimal number with no powers of 1010 Your calculator can do thisYour calculator can do this

• Round to just 2 significant figures Round to just 2 significant figures

• Match colors to the numberMatch colors to the number

• You calculate 26.8 kYou calculate 26.8 kΩΩ is needed is needed

• 26.8 k26.8 kΩΩ =26,800 =26,800 Ω Ω = 27,000 = 27,000

• 2 = Red, 7 = Violet, 000 = Orange (3)2 = Red, 7 = Violet, 000 = Orange (3)

• Need a Red Violet Orange resistorNeed a Red Violet Orange resistor

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PracticePractice#1 #2 Zeroes Tol Value

11 22 00 10%10% 1212 12 12 ΩΩ 10% 10%

BrownBrown RedRed BlackBlack SilverSilver

66 88 22 10%10% 68006800 6.8 k6.8 kΩΩ 10% 10%

910 910 ΩΩ 10% 10%

4.7 M4.7 MΩΩ 10% 10%

1.0 1.0 ΩΩ 10% 10%

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Record your answers on page 26 in the lab manual, #3

Range of Acceptable ValuesRange of Acceptable Values• What range of value might this What range of value might this

resistor have:resistor have:

• Red Violet Orange GoldRed Violet Orange Gold

• 2 7 000 5% = 27 k2 7 000 5% = 27 kΩΩ

• Maximum = 27 kMaximum = 27 kΩΩ (1.05) = 28,350 (1.05) = 28,350 Ω Ω

• Minimum = 27 kMinimum = 27 kΩΩ (0.95) = 25,650 (0.95) = 25,650 Ω Ω

• Record your answers on page 26 in the lab manual, #5Record your answers on page 26 in the lab manual, #5

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5 Band Resistors5 Band Resistors• Number Number Number Multiplier ToleranceNumber Number Number Multiplier Tolerance

• Tolerance is always under 5%Tolerance is always under 5%• RedRed 2%2%• BrownBrown 1%1%• GreenGreen 0.5%0.5%• BlueBlue 0.25%0.25%• VioletViolet 0.1%0.1%• Don’t bother memorizing these valuesDon’t bother memorizing these values

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PracticePractice#1 #2 #3 Zeroes Tol Value

OrangeOrange BlueBlue GreenGreen GoldGold RedRed

33 66 55 0.10.1 2%2% 365x0.1365x0.1 36.5 36.5 ΩΩ 2% 2%

RedRed VioletViolet YellowYellow BrownBrown GreenGreen

GreyGrey RedRed GreenGreen RedRed BrownBrown

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PracticePractice#1 #2 #3 Zeroes Tol Value

11 44 77 22 1%1% 14,70014,700 14.7 k14.7 kΩΩ 1%1%

BrownBrown YellowYellow VioletViolet RedRed BrownBrown

39.2 39.2 ΩΩ 1% 1%

9.76 k9.76 kΩΩ 1% 1%

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Lab 16 Prep Enter on Page 121Lab 16 Prep Enter on Page 121#1 #2 Zeroes Tol Value

44 77 11 5%5% 470470 470 470 ΩΩ 5% 5%

YellowYellow VioletViolet BrownBrown GoldGold

1.5 k1.5 kΩΩ 5% 5%

3.3 k3.3 kΩΩ 5% 5%

8.2 k8.2 kΩΩ 5% 5%

270 k270 kΩΩ 5% 5%

1.0 M1.0 MΩΩ 5% 5%

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Percent DifferencePercent Difference• To calculate the percent difference:To calculate the percent difference:

• (Observed – Accepted) (Observed – Accepted) x 100x 100 Accepted Accepted

• Observed is what you measureObserved is what you measure

• Accepted is the color codeAccepted is the color code

• Brown Green Brown = 150 Brown Green Brown = 150 ΩΩ

• In lab you measure 146 In lab you measure 146 ΩΩ

• (146 -150) (146 -150) x 100 = -2.7% (Reading low)x 100 = -2.7% (Reading low) 150 150

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Variable ResistorsVariable Resistors• Rheostat - a two-terminal Rheostat - a two-terminal

device whose resistance can device whose resistance can be changed to control be changed to control currentcurrent

• Potentiometer - a three-Potentiometer - a three-terminal device whose terminal device whose resistance from each end to resistance from each end to the wiper can be changed by the wiper can be changed by moving its wiper to split moving its wiper to split voltage.voltage.

• A pot can be connected as a A pot can be connected as a rheostat.rheostat.

• Fill in page 26, Question 6Fill in page 26, Question 6

SwitchesSwitches

• Switches break (open) OR make Switches break (open) OR make (close) circuit connections.(close) circuit connections.

FusesFuses• A fuse protects circuits or devices from A fuse protects circuits or devices from

excessive current flow.excessive current flow.

Fuse ratings: currentvoltageresponse time

Optical IndicatorsOptical Indicators

• Incandescent Incandescent Light Sources Light Sources

• Neon Indicators Neon Indicators

• Solid-State Solid-State Light SourcesLight Sources

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• Meters detect and measure the Meters detect and measure the invisible action of electrons.invisible action of electrons.

• Meters are indispensable in Meters are indispensable in examining the operation of a circuit.examining the operation of a circuit.– Below are typical analog metersBelow are typical analog meters

MetersMeters

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DC Test EquipmentDC Test Equipment

• Meters are generally classified as Meters are generally classified as digital (numbers) or analog (moving digital (numbers) or analog (moving needle)needle)

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METER TYPESMETER TYPES• AnalogAnalog: Uses a meter movement. All : Uses a meter movement. All

scales are on one surface area. Less scales are on one surface area. Less accuracy. accuracy.

• DigitalDigital: Uses a digital display. More : Uses a digital display. More accurate. Often auto-ranging.accurate. Often auto-ranging.

• VOMVOM: Volt-Ohm-Milliammeter, : Volt-Ohm-Milliammeter, • DMMDMM: Digital MultiMeter. : Digital MultiMeter.

Digital type. Most common. Digital type. Most common. High accuracy at low cost.High accuracy at low cost.

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• Combines the voltmeter, ammeter, Combines the voltmeter, ammeter, and the ohmmeter into a single and the ohmmeter into a single instrument.instrument.

• An analog multimeter is also referred An analog multimeter is also referred to as a to as a volt-ohm-milliammetervolt-ohm-milliammeter (VOM). (VOM).

• A digital multimeter is A digital multimeter is also referred to as a also referred to as a DMMDMM..

MultimeterMultimeter

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Analog MetersAnalog Meters• Electric current generates a magnetic fieldElectric current generates a magnetic field• The strength of the field depends on the The strength of the field depends on the

magnitude of the currentmagnitude of the current• The bigger the current, the more the The bigger the current, the more the

needle movesneedle moves

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Digital Meters - DVMDigital Meters - DVM

• At ITT you will use digital metersAt ITT you will use digital meters– DMMs use analog to digital chipsDMMs use analog to digital chips

• Some students purchase their own Some students purchase their own meter ($30 buys a good one)meter ($30 buys a good one)

107

• Measures the voltage between two Measures the voltage between two points in a circuit.points in a circuit.

• Can be considered a pressure gauge.Can be considered a pressure gauge.

VoltmeterVoltmeter

108

Measuring Voltage with a DVMMeasuring Voltage with a DVM• Red banana plug in the V-Red banana plug in the V-ΩΩ connection connection• Black banana plug in the Common Black banana plug in the Common

connectionconnection• Push button for DC readingsPush button for DC readings• Push button for voltage measurementsPush button for voltage measurements• Set range to maximumSet range to maximum• Attach leads between two points whose Attach leads between two points whose

voltage difference you want to measurevoltage difference you want to measure– Red closer to positive, black closer to negativeRed closer to positive, black closer to negative

• Turn on the DVMTurn on the DVM

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Digital Volt Meter - DVMDigital Volt Meter - DVM

• Turn on the power supply for the Turn on the power supply for the circuitcircuit

• Adjust range if neededAdjust range if needed– Start high and keep lowering the range Start high and keep lowering the range

until you see a “1” and then increase until you see a “1” and then increase the rangethe range

• Record measurementRecord measurement

• Remove meterRemove meter

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Circuit ConnectionCircuit Connection

• Voltmeters are always connected in Voltmeters are always connected in parallel with the components that parallel with the components that you want to measure for a voltage you want to measure for a voltage dropdrop

111

• Measures current in a circuit.Measures current in a circuit.• Can be considered a flow meter.Can be considered a flow meter.• Measures the number of electrons Measures the number of electrons

per second flowing past a given per second flowing past a given point in a circuit.point in a circuit.

AmmeterAmmeter

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Measuring Current with a DMMMeasuring Current with a DMM• Red banana plug in the Red banana plug in the AmpAmp connection connection• Black banana plug in the Common Black banana plug in the Common

connectionconnection• Push button for DC readingsPush button for DC readings• Push button for current measurementsPush button for current measurements• Set range to maximumSet range to maximum• Break the circuit where you want to Break the circuit where you want to

measure the current, and rejoin the two measure the current, and rejoin the two points with the meterpoints with the meter

• Turn on the DMMTurn on the DMM

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Digital Volt Meter - DMMDigital Volt Meter - DMM

• Turn on the power supply for the Turn on the power supply for the circuitcircuit





114


• Ammeters are always connected in Ammeters are always connected in series with the components that you series with the components that you want to measure for a current flowwant to measure for a current flow

– Red toward positive terminalRed toward positive terminal

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• An Ohmmeter measures resistance by placing a small voltage across the An Ohmmeter measures resistance by placing a small voltage across the device to be measured, inducing a current flow through the device.device to be measured, inducing a current flow through the device.

• The amount of current The amount of current indicates the resistanceindicates the resistance

• Any current from any other Any current from any other source makes the reading source makes the reading false and may destroy the meterfalse and may destroy the meter

OhmmeterOhmmeter

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Measuring ResistanceMeasuring Resistance• Red banana plug in the V-Red banana plug in the V-ΩΩ connection connection• Black banana plug in the Common Black banana plug in the Common

connectionconnection• Push button for DC readingsPush button for DC readings• Push button for Ohm (Push button for Ohm (ΩΩ)) measurements measurements• Set range to maximumSet range to maximum• Remove the component from the circuitRemove the component from the circuit• Attach a lead to each end of the Attach a lead to each end of the

componentcomponent• Turn on the DMMTurn on the DMM

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Digital Resistance MeterDigital Resistance Meter





118


• Ohm meters are always connected in Ohm meters are always connected in parallel with the components that parallel with the components that you want to measure for resistanceyou want to measure for resistance

• Safer to disconnect component Safer to disconnect component completely from the circuitcompletely from the circuit

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• Use an ohmmeter to determine whether a Use an ohmmeter to determine whether a circuit is:circuit is:– Open:Open: Has infinite resistance because no Has infinite resistance because no

current flows through it.current flows through it.– Shorted:Shorted: Has zero ohms of resistance because Has zero ohms of resistance because

current flows through it without developing a current flows through it without developing a voltage drop.voltage drop.

– Closed: Closed: A complete path for current where A complete path for current where resistance varies depending on the resistance varies depending on the components in the circuit.components in the circuit.

• Continuity checkContinuity check– The testing for an open, short, or closed The testing for an open, short, or closed

circuit.circuit.

Ohmmeter TroubleshootingOhmmeter Troubleshooting

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Don’t Hurt the MetersDon’t Hurt the Meters

• Do NOTs:Do NOTs:

• Do NOT connect an ammeter in Do NOT connect an ammeter in parallel with a componentparallel with a component

• Do NOT connect an ohmmeter to a Do NOT connect an ohmmeter to a component in a live circuitcomponent in a live circuit

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Tips and TricksTips and Tricks

• When measuring voltage, if the When measuring voltage, if the reading is positive, the red lead is reading is positive, the red lead is touching a point with a higher touching a point with a higher voltage than the black leadvoltage than the black lead

• When measuring current, if the When measuring current, if the reading is positive, the electrons are reading is positive, the electrons are flowing in the black lead and out the flowing in the black lead and out the red leadred lead

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Measuring Affects ValuesMeasuring Affects Values

• Attaching the meter to a circuit affects the Attaching the meter to a circuit affects the current and voltages in the circuitcurrent and voltages in the circuit

• Meters are designed to have the minimum Meters are designed to have the minimum possible influence on the circuit.possible influence on the circuit.

• Voltmeter Loading: Defined as undesired Voltmeter Loading: Defined as undesired change to circuit parameters when the change to circuit parameters when the measuring instrument is connected to the measuring instrument is connected to the circuit.circuit.

• The more expensive the meter, the smaller The more expensive the meter, the smaller the effect it has on the circuitthe effect it has on the circuit

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OscilloscopeOscilloscope• Oscilloscope (o’scope, scope) is Oscilloscope (o’scope, scope) is

used to visualize the relationship used to visualize the relationship between circuit voltage and timebetween circuit voltage and time

124

VariationsVariations• Oscilloscopes vary from simple to Oscilloscopes vary from simple to

complex (and very expensive)complex (and very expensive)

• The scopes at ITT display variations The scopes at ITT display variations of voltage with respect to timeof voltage with respect to time

Time

Voltage

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DC VoltagesDC Voltages• Oscilloscopes are very helpful in AC Oscilloscopes are very helpful in AC

Electronics.Electronics.• DC voltages are generally constant and DC voltages are generally constant and

displaying them on a scope will provide displaying them on a scope will provide little additional informationlittle additional information

Time

Voltage

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ITT ScopesITT Scopes• CRT type of display.CRT type of display.• Dual display – can Dual display – can

show two voltages show two voltages at onceat once

• Can add or subtract voltages and display Can add or subtract voltages and display the resultsthe results

• Controls can adjust voltage and time Controls can adjust voltage and time displays.displays.

• Vertical and Horizontal positioning.Vertical and Horizontal positioning.

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Wait Until AC ElectronicsWait Until AC Electronics

• In AC Electronics next quarter, you In AC Electronics next quarter, you will study the Oscilloscope in detailwill study the Oscilloscope in detail

128

Chapter SummaryChapter Summary

• One coulomb is the charge on 6.25 x 10One coulomb is the charge on 6.25 x 101818 electronselectrons

• One volt is the potential difference One volt is the potential difference (voltage or EMF) between two points when (voltage or EMF) between two points when one joule of energy is used to move one one joule of energy is used to move one coulomb of charge from one point to the coulomb of charge from one point to the otherother

• One ampere is the amount of current that One ampere is the amount of current that exists when one coulomb of charge exists when one coulomb of charge moves through a given cross-sectional moves through a given cross-sectional area of material in one secondarea of material in one second

• One ohm is the resistance when there is One ohm is the resistance when there is one ampere of current in a material with one ampere of current in a material with one volt applied across the materialone volt applied across the material

1 Unit Two: Voltage, Current, and Resistance John Elberfeld [email protected] ET115 DC Electronics.

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