What is electronics

Physics 110Physics 110

Fundamentals of Fundamentals of ElectronicsElectronics

Chapter 2Chapter 2

DC NetworksDC Networks

Review TopicsReview Topics Scientific NotationScientific Notation Units of MeasureUnits of Measure

What is Electricity?What is Electricity? From the Greek word “elektron”From the Greek word “elektron”

that means “amber”that means “amber” There are two types of electricity:There are two types of electricity:

– Static Electricity Static Electricity - no motion of free charges- no motion of free charges– Current Electricity Current Electricity - motion of free charges- motion of free charges

» Direct Current (DC)Direct Current (DC)

» Alternating Current (AC)Alternating Current (AC)

2.2 Current2.2 Current

CurrentCurrent is the rate of flow of charge through is the rate of flow of charge through a conductor.a conductor.– ConductorConductor

» materials with free electronsmaterials with free electrons

» e.g. copper, aluminum, gold, most metalse.g. copper, aluminum, gold, most metals

– InsulatorInsulator» materials with no free electronsmaterials with no free electrons

» e.g. glass, plastics, ceramics, woode.g. glass, plastics, ceramics, wood

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Equation for CurrentEquation for Current

I=Q/tI=Q/t

I = the current in Amperes (A)I = the current in Amperes (A)

Q = the amount of charge in Coulombs (C)Q = the amount of charge in Coulombs (C)

t = the time measured in seconds (s)t = the time measured in seconds (s)

The charge of an electron is 1.6 x 10The charge of an electron is 1.6 x 10-19-19 C C

Effect of Electric Currents on the BodyEffect of Electric Currents on the Body

0.001 A can be felt0.001 A can be felt 0.005 A is painful0.005 A is painful 0.010 A0.010 A causes involuntary muscle causes involuntary muscle

contractionscontractions 0.015 A causes loss of muscle control0.015 A causes loss of muscle control 0.070 A can be fatal if the current last for more 0.070 A can be fatal if the current last for more

than 1 second than 1 second

Example Problem 2.0Example Problem 2.0

How much charge will pass through a How much charge will pass through a conductor in 0.1 seconds if the current is conductor in 0.1 seconds if the current is 0.5 Amperes?0.5 Amperes?

How many electrons are required for this How many electrons are required for this much charge?much charge?

Example Problem 2.1Example Problem 2.1 Determine the current in amperes through a Determine the current in amperes through a

wire if 18.726 x 10wire if 18.726 x 101818 electrons pass through electrons pass through the conductor in 0.02 minutes.the conductor in 0.02 minutes.

Example Problem 2.2Example Problem 2.2 How long will it take 120 C of charge to How long will it take 120 C of charge to

pass through a conductor if the current is pass through a conductor if the current is 2 A?2 A?

Example Problem 2.3 and 2.4Example Problem 2.3 and 2.4

Write the following in the most convenient form using Table 2.1:Write the following in the most convenient form using Table 2.1:

(a) 10,000 V(a) 10,000 V

(b) 0.00001 A(b) 0.00001 A

(c) 0.004 seconds(c) 0.004 seconds

(d) 630,000,000 Watts(d) 630,000,000 Watts

(e) 0.00006 A(e) 0.00006 A

Wire Gauge?Wire Gauge?

AWG = American Wire GaugeAWG = American Wire Gauge AWG numbers indicate the size of the AWG numbers indicate the size of the

wire….but in reverse.wire….but in reverse. For example, No. 12 gauge wire has a For example, No. 12 gauge wire has a

larger diameter than a No. 14 gauge wire.larger diameter than a No. 14 gauge wire.

2.3 Voltage2.3 Voltage

VoltageVoltage is the measure of the potential to is the measure of the potential to move electrons.move electrons.

Sources of VoltageSources of Voltage– BatteriesBatteries (DC) (DC)– Wall Outlets (AC)Wall Outlets (AC)

The term The term ground ground refers to a zero voltage or refers to a zero voltage or earth potential.earth potential.

Digital MultimetersDigital Multimeters

MeasurementMeasurement DeviceDevice Circuit SymbolCircuit Symbol

VoltageVoltage VoltmeterVoltmeter

CurrentCurrent AmmeterAmmeter

ResistanceResistance OhmeterOhmeter

More on BatteriesMore on Batteries Positive (+) and Negative (-) terminalsPositive (+) and Negative (-) terminals Batteries use a chemical reaction to create voltage.Batteries use a chemical reaction to create voltage. Construction: Two different metals and AcidConstruction: Two different metals and Acid

– e.g. Copper, Zinc, and Citrus Acide.g. Copper, Zinc, and Citrus Acid– e.g. Lead, Lead Oxide, Sulfuric Acide.g. Lead, Lead Oxide, Sulfuric Acid– e.g. Nickel, Cadmium, Acid Pastee.g. Nickel, Cadmium, Acid Paste

Batteries “add” when you connect them in series.Batteries “add” when you connect them in series. Circuit Symbol:Circuit Symbol:

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Equation for VoltageEquation for Voltage

V=W/QV=W/Q

V = the voltage in volts (V)V = the voltage in volts (V)

Q = the amount of charge in Coulombs (C)Q = the amount of charge in Coulombs (C)

W = the energy expended in Joules (J)W = the energy expended in Joules (J)

Example Problem 2.7Example Problem 2.7 Determine the energy expended by a 12 V Determine the energy expended by a 12 V

battery in moving 20 x 10battery in moving 20 x 101818 electrons electrons between its terminals.between its terminals.

(a) If 8 mJ of energy is expended moving (a) If 8 mJ of energy is expended moving 200 200 C from one point in an electrical C from one point in an electrical circuit to another, what is the difference in circuit to another, what is the difference in potential between the two points?potential between the two points?

(b) How many electrons were involved in (b) How many electrons were involved in the motion of charge in part (a)?the motion of charge in part (a)?


2.4 Resistance and Ohm’s Law2.4 Resistance and Ohm’s Law

ResistanceResistance it the measure of a material’s ability it the measure of a material’s ability to resist the flow of of electrons.to resist the flow of of electrons.

It is measure in Ohms (It is measure in Ohms ().). Ohm’s Law:Ohm’s Law:

V = I RV = I R

V or E = voltageV or E = voltage

I = currentI = current

R = resistanceR = resistance

Example Problem 2.9Example Problem 2.9 Determine the voltage drop across a 2.2 kDetermine the voltage drop across a 2.2 k

resistor if the current is 8 mA.resistor if the current is 8 mA.

Example Problem 2.10Example Problem 2.10 Determine the current drawn by a toaster Determine the current drawn by a toaster

having an internal resistance of 22 having an internal resistance of 22 if the if the applied voltage is 120 V.applied voltage is 120 V.

Example Problem 2.11Example Problem 2.11 Determine the internal resistance of an Determine the internal resistance of an

alarm clock that draws 20 mA at 120 V.alarm clock that draws 20 mA at 120 V.

Equation for ResistanceEquation for Resistance

= resistivity of the material from tables= resistivity of the material from tables

AR

= length of the material in feet (ft)= length of the material in feet (ft)

A = area in circular mils (CM)A = area in circular mils (CM)

Example Problem 2.12Example Problem 2.12 Determine the resistance of 100 yards of Determine the resistance of 100 yards of

copper wire having and 1/8 inch diameters.copper wire having and 1/8 inch diameters.

Concept QuestionsConcept Questions

How can you determine the current through How can you determine the current through a resistor if you know the voltage across it? a resistor if you know the voltage across it?

How can you change the resistance of a How can you change the resistance of a resistor? resistor?

Temperature dependence of ResistanceTemperature dependence of Resistance

R = resistancesR = resistances

t = temperaturest = temperatures

= temperature coefficient from tables = temperature coefficient from tables

)tt(1RR 12112

Example Problem 2.15Example Problem 2.15 The resistance of a copper conductor is 0.3 The resistance of a copper conductor is 0.3 at at

room temperature (20°C). Determine the room temperature (20°C). Determine the resistance of the conductor at the boiling point of resistance of the conductor at the boiling point of water (100°C). water (100°C).

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Resistor Color CodesResistor Color Codes00 BlackBlack

11 BrownBrown

22 RedRed

33 OrangeOrange

44 YellowYellow

55 GreenGreen

66 BlueBlue

77 VioletViolet

88 GrayGray

99 WhiteWhite

Tolerance Tolerance

5%5% GoldGold

10% 10% SilverSilver

Memorize this table.

Example Problem 2.17Example Problem 2.17 Determine the manufacturer’s guaranteed Determine the manufacturer’s guaranteed

range of values for a carbon resistor with range of values for a carbon resistor with color bands of Blue, Gray, Black and Gold. color bands of Blue, Gray, Black and Gold.

Example Problem 2.18Example Problem 2.18 Determine the color coding for a 100 kDetermine the color coding for a 100 k

resistor with a 10% tolerance. resistor with a 10% tolerance.

Total Resistance for Resistors in SeriesTotal Resistance for Resistors in Series

21T RRR

Total Resistance for Resistors in ParallelTotal Resistance for Resistors in Parallel

21T R

1

R

1

R

1

PotentiometersPotentiometers They are They are three terminal devicesthree terminal devices with a with a

knob.knob. The knob moves a The knob moves a sliderslider which changes the which changes the

resistance between the terminals.resistance between the terminals. Circuit Symbols:Circuit Symbols:

What is the difference between E and V?What is the difference between E and V?

E is the voltage supplied by a battery.E is the voltage supplied by a battery. V is the voltage measured across a resistor.V is the voltage measured across a resistor.

2.5 Power, Energy, Efficiency2.5 Power, Energy, Efficiency

PowerPower is the measure of the rate of energy is the measure of the rate of energy conversion.conversion.

Resistors convert Resistors convert electrical energyelectrical energy into into heat energyheat energy.. Equation for Power:Equation for Power:

P = I E Power Delivered by a BatteryP = I E Power Delivered by a Battery

P = I V Power Dissipated by a ResistorP = I V Power Dissipated by a Resistor What are some other ways that we can write this What are some other ways that we can write this

equation?equation?

Example Problem 2.19Example Problem 2.19 Determine the current drawn by a 180 W Determine the current drawn by a 180 W

television set when connected to a 120 V television set when connected to a 120 V outlet.outlet.

Simple Circuit ProblemSimple Circuit Problem Using circuit symbols, draw a circuit for a Using circuit symbols, draw a circuit for a

9V battery connected to a 109V battery connected to a 10 resistor. resistor. Draw and label the direction of Draw and label the direction of

conventional currentconventional current.. Now include a voltmeter in your sketch that Now include a voltmeter in your sketch that

will measure the voltage drop across the will measure the voltage drop across the resistors. What will it read?resistors. What will it read?

Include a ammeter that will measure the Include a ammeter that will measure the current through the resistor. What will it current through the resistor. What will it read?read?

Simple Circuit ProblemSimple Circuit Problem How much power does the battery deliver?How much power does the battery deliver? How much power does the resistor How much power does the resistor

dissipate?dissipate?

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Note: Equations will be provided Note: Equations will be provided on the chalk board during the on the chalk board during the exam. exam.

However, you must know what However, you must know what each variable represents and each variable represents and what units are used for each.what units are used for each.

Example Problem 2.20Example Problem 2.20 Determine the resistance of a 1200W Determine the resistance of a 1200W

toaster that draws 10A.toaster that draws 10A.

Energy and power are related:Energy and power are related:

W = P tW = P t

W = energy in JoulesW = energy in Joules

P = power in WattsP = power in Watts

t = time in secondst = time in seconds

Example Problem 2.21Example Problem 2.21 Determine the cost of using the following appliances for the time indicated if the Determine the cost of using the following appliances for the time indicated if the

average cost is 9 cents/kWh.average cost is 9 cents/kWh.

– (a) 1200W iron for 2 hours(a) 1200W iron for 2 hours

– (b) 160W color TV for 3 hours and 30 minutes(b) 160W color TV for 3 hours and 30 minutes

– (c) Six 60W bulbs for 7 hours.(c) Six 60W bulbs for 7 hours.

EfficiencyEfficiency

%100P

P

i

o

loi PPP

W746hp1

Example Problem 2.22Example Problem 2.22 Determine the efficiency of operation and Determine the efficiency of operation and

power lost in a 5hp DC motor that draws power lost in a 5hp DC motor that draws 18A as 230V.18A as 230V.

2.6 Series DC Networks2.6 Series DC Networks

Two elements are in series if they have only Two elements are in series if they have only one terminal in common that is not connected one terminal in common that is not connected to a third current carrying component.to a third current carrying component.

Total ResistanceTotal Resistance

N321T R...RRRR Current through a SeriesCurrent through a Series

TR

EI

Consider Figure 2.29.Consider Figure 2.29.» E=24V, RE=24V, R11=2=2, R, R22=4=4, R, R33=6=6

What is RWhat is RTT??

What is I?What is I? What is VWhat is V11, V, V22 and V and V33??

What is PWhat is P11, P, P22, P, P33, and P, and PEE??

Kirchhoff’s Voltage LawKirchhoff’s Voltage Law

““The algebraic sum of the voltage rises and The algebraic sum of the voltage rises and drops around a closed path must be equal to drops around a closed path must be equal to zero.”zero.”

0VV dropsrises

Voltage-divider rule Voltage-divider rule – ““The voltage across any resistor in a series is some The voltage across any resistor in a series is some

fraction of the battery voltage.”fraction of the battery voltage.”

T

xx R

ERV

11

Express these numbers with only Express these numbers with only three significant figures and in the three significant figures and in the

most convenient form.most convenient form.

0.038457 C0.038457 C 0.0012878 A0.0012878 A 12869.578 V12869.578 V 0.57382 W0.57382 W

2.7 Parallel DC Networks2.7 Parallel DC Networks

Two elements are in parallel if they have two Two elements are in parallel if they have two terminals in common.terminals in common.

Total ResistanceTotal Resistance

N321T R

1...

R

1

R

1

R

1

R

1

Source CurrentSource Current

TR

EI

Concept TestConcept Test

For resistors in For resistors in seriesseries, what is the same for , what is the same for every resistor? R, V or I?every resistor? R, V or I?

» Answer: IAnswer: I

For resistors in parallel, what is the same For resistors in parallel, what is the same for every resistor? R, V or I?for every resistor? R, V or I?

» Answer: VAnswer: V

Kirchhoff’s Current LawKirchhoff’s Current Law

““The sum of the current entering a junction The sum of the current entering a junction must equal to the current leaving.”must equal to the current leaving.”

leavingentering II

Example Problem 2.28Example Problem 2.28 Using Kirchhoff’s current law, determine Using Kirchhoff’s current law, determine

the currents Ithe currents I33 and I and I66 for the system of for the system of

Figure 2.38Figure 2.38

Consider Figure 2.32.Consider Figure 2.32.» EE11=100V=100V

» EE22=50V=50V

» EE33=20V=20V

» RR11=10=10

» RR22=30=30

» RR33=40=40

What is I?What is I? What is VWhat is V22??


Find VFind V11 and V and V22 of Figure 2.33 using of Figure 2.33 using

Kirchhoff’s voltage law.Kirchhoff’s voltage law.

Voltage Sources in SeriesVoltage Sources in Series

Current-divider rule Current-divider rule – ““The current through any resistor in parallel with The current through any resistor in parallel with

other resistors is some fraction of the source other resistors is some fraction of the source current.”current.”

x

Tx R

IRI

Example Problem 2.26Example Problem 2.26 Determine the following for the parallel network in Fig. 2.36.Determine the following for the parallel network in Fig. 2.36.

– (a) R(a) RTT

– (b) I(b) I

– (c) I(c) I22

– (d) P(d) P33


2.8 Series-Parallel Networks2.8 Series-Parallel Networks

Determine the following for the network in Determine the following for the network in Fig. 2.41.Fig. 2.41.– (a) R(a) RTT

– (b) I(b) I

– (c) I(c) I1 1 and Iand I22

– (d) V(d) V11

What is electronics

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