VoltageVoltage

Chapter 3Chapter 3

Voltage (V or E)Voltage (V or E)

Supplies the force or pressure required to move electrons

through a circuit.

Unit – Volt (V)

AKA – Electromotive Force EMF

Voltage SourcesVoltage Sources

Friction – Van de Graaf Generator

Voltage SourceVoltage Source

Generator – Most Common

Voltage SourceVoltage Source

Cell – Battery: Chemical Reaction

Voltage SourceVoltage Source

Photovoltaic CellLight → Voltage

Voltage SourceVoltage Source

ThermocoupleHeat → Voltage

Voltage SourceVoltage Source

Piezoelectric EffectPressure → Voltage

Cells and BatteriesCells and Batteries

Primary CellsCannot be Recharged

Cells and BatteriesCells and Batteries

Secondary CellsCan be Recharged

Connecting Voltage SourcesConnecting Voltage Sources

Series Aiding Series Opposing

--++

--+

+

Voltage SourcesVoltage SourcesVoltage sources added in Series

increase the Voltage and the Current stays the same.

V = 1.5v I = 1A

V = 4.5v I = 1A

V = 4.5v I = 1A

Voltage SourcesVoltage SourcesVoltage sources added in Parallel

increase the Current and the Voltage stays the same.

V = 1.5v I = 1A

V = 1.5v I = 3A

V=1.5v I =3A

ExampleExample Battery: V = 1.5v, I = 1A

V=3vI= 3A

V=3v I=1A I=1A I=1A

V=3v I=3A

Battery: V = 1.5v and I = 100mA

9v100mA 100mA 100mA 100mA 100mA

VT = 9vIT =500mA

VT = 9v and IT = 500ma

VT = 9vIT =500mA

Voltage RiseVoltage Rise

Voltage Rise can be defined as the energy added to a circuit. 

Voltage DropVoltage Drop

A Voltage Drop is defined as the energy removed or used in a circuit.

Voltage DropVoltage Drop

Earth GroundEarth GroundZero Voltage reference point.Limits build up of electrical charge.Limits exposure to high voltages.

Electrical GroundElectrical Ground

Ground is defined as the zero reference point which against

all voltages are measured.

Electrical Ground in a CarElectrical Ground in a Car

Jumping a CarJumping a Car

BadBattery

Ohm’s LawOhm’s LawThe Current(I) in a circuit is directly

proportional to the Voltage(E,V) and inversely proportional to the

Resistance(R).

I = VR

Ohm’s LawOhm’s Law

RI

VFind: V

V = IxR

Ohm’s LawOhm’s Law

RI

VFind: R

R = V/I

Ohm’s LawOhm’s Law

RI

VFind: I

I = V/R

Ohm’s Law UnitsOhm’s Law Units

RΩIA

Vv

Ohm’s Law UnitsOhm’s Law Units

RkΩImA

V(v)

Ohm’s Law ExampleOhm’s Law Example

RΩIA

Vv

R=2Ω, V=12vFind: I

I = V/R =12v/2Ω

I = 6A

Ohm’s Law ExampleOhm’s Law Example

RkΩImA

Vv

V=120, I=60mAFind: R

R = V/I =120v/60mA

R = 2kΩ

Ohm’s Law ExampleOhm’s Law Example

RkΩImA

Vv

R=10kΩ, I=12mAFind: V

V = IxR =12mAx10kΩ

V = 120v

Wheel of AnswersWheel of Answers

RΩIA

Vv

RkΩImA

Vv

PowerPowerPower is how fast work is done.

Work is done when force causes motion.

Electric Force: Voltage

Moving: Electrons

PowerPowerPower: P

Unit for Power: WattWatt: W

P = IV

Power LawPower Law

VI

PFind: P

P = IxV

Power LawPower Law

VI

PFind: V

V = P/I

Power LawPower Law

VI

PFind: I

I = P/V

Power Law UnitsPower Law Units

VVIA

PW

Power Law UnitsPower Law Units

VVImA

PmW

How much power does a 12V computer fan use if it is drawing 1.5A?

V = 12VI = 1.5A

P=IV

P=(1.5A)(12V)

P = (18W)

Combining Ohm’s and Power LawsCombining Ohm’s and Power Laws

RIVP = I2R

V2

RP =

Classwork Classwork Read the following Chapters:Read the following Chapters:

»Chapter 2: AllChapter 2: All

»Chapter 3: AllChapter 3: All

»Chapter 4: Pages 32-44Chapter 4: Pages 32-44

»Chapter 5: Pages 49-52Chapter 5: Pages 49-52

Answer the questions after each section:Answer the questions after each section:Write down question and answer!!!Write down question and answer!!!

• Perform Self-Test at the end of the chapter Perform Self-Test at the end of the chapter Write down question and answer!!!Write down question and answer!!!