What is DC Electricity.What is DC Electricity.

Chapter 2Chapter 2

ResistanceResistance

The property of a material to inhibit the flow of current.

ResistorResistor

ResistorResistor

Molded Carbon Composite

ResistorResistor

Wirewound

Film

Molded Carbon Composite

Wire woundWire wound

FilmFilm

Surface MountTechnology

SMT

ResistivityResistivity

AL

Resistivity: ExampleResistivity: ExampleA 1m long piece of gold has a cross

sectional area of 0.1cm2 . The resistivity of gold at 20°C is

2.24 X 10-8 ohm-meters.ρ

ρ =2.24 X 10-8 ohm-metersA = 0.1cm2 L = 1m

L = 1m

Resistivity: GoldResistivity: Goldρ =2.24 X 10-8 ohm-metersA = 0.1cm2 L = 1m

R =ρL A

R =(2.24 X 10-8 Ώ-m)(1m)

0.00001m2

R =0.00224 Ώ

Resistivity: CarbonResistivity: Carbonρ =50 X 10-5 ohm-metersA = 0.1cm2 L = 1m

R =ρL A

R =(50 X 10-5 Ώ-m)(1m)

0.00001m2

R =50 Ώ

Resistor Color CodeResistor Color Code

0

12

3

45

6

78

9

ToleranceTolerance

5%

The measure of how good a component is. How close it is to the

actual value.

10% 20%Gold Silver No Band

ToleranceTolerance

100100ΩΩ

5%: 95-1055%: 95-105ΩΩ

10%: 90-11010%: 90-110ΩΩ

20%: 80-12020%: 80-120ΩΩ

}Digits

36

Multiplier00000

Tolerance5 %

R =3600000 Ώ or 3.6M Ώ

}Digits

47

Multiplier

Tolerance20 %

R =36 Ώ

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

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

ExamplExampl

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

V=3vI= 3A

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

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 = ER

Ohm’s LawOhm’s Law

RI

EFind: E

E = IxR

Ohm’s LawOhm’s Law

RI

EFind: R

R = E/I

Ohm’s LawOhm’s Law

RI

EFind: I

I = E/R

Ohm’s Law UnitsOhm’s Law Units

RΩIA

Ev

Ohm’s Law UnitsOhm’s Law Units

RkΩImA

E(v)

Ohm’s Law UnitsOhm’s Law Units

RMΩIμA

E(v)

Ohm’s Law ExampleOhm’s Law Example

RΩIA

Ev

R=2Ω, E=12vFind: I

I = E/R =12v/2Ω

I = 6A

Ohm’s Law ExampleOhm’s Law Example

RkΩImA

Ev

E=120, I=60mAFind: R

R = E/I =120v/60mA

R = 2kΩ

Ohm’s Law ExampleOhm’s Law Example

RkΩImA

Ev

R=10kΩ, I=12mAFind: E

E = IxR =12mAx10kΩ

I = 120v

Wheel of AnswersWheel of Answers

RΩIA

Ev

RkΩImA

Ev