Basics of Electricity 22.10

8/8/2019 Basics of Electricity 22.10

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Measuring ElectricityMeasuring Electricity

q Voltageforce or pressure caused bythe separation of electrons and protons. Unit of measurement: Volts (V)

q

Currentthe path provided for the freeflow of electrons in an electrical circuit. Unit of measurement: Ampere (amp)

q Resistanceimpedance or oppositionto the flow of electrons: conductor=lowresistance;insulators=high resistance.

Unit of measurement: ohms ()


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Parts of An AtomParts of An Atom

qProton

qNeutron

qElectron

e l e c t r o n

n e u t r o n

p r o t o n


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Flowing ElectronsFlowing Electrons

qElectrons are negatively charged

q

Protons are positively chargedqOpposite charges attract

qVelocity of electrons keep them in

orbit around nucleusqElectrons pulled free from the atom

is what we call electricity!


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Dynamic ElectricityDynamic Electricity

qElectricity can be viewed as a

dynamic process.

qDynamic means changing.

qElectrons are changingmoving

from one atom to another.qThis flowing of electrons is called an

electrical current.


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Static ElectricityStatic Electricity

q Static means stationary or unchanging.

q Electrons have been loosened from

the atom and stay in one place.

q The electrons have voltage but lack a

current.

q A conductor supplies the currentor

pathfor static electricity to discharge.


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ConductorsConductors

qConductors have a large number of

loosely attached electrons.

qThese electrons can easily be freed

from the nucleus of the atom when

voltage is applied.


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Examples of ConductorsExamples of Conductors

qMetals Gold

Silver

Copper (Cat 5 Cable)

qWater

qHumans


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InsulatorsInsulators

q Material with a high resistance to

electrical current.

q Electron orbits are very close to thenucleus.

q Examples:

Plastic Glass

Wood

Air and other gases


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Multimeter BasicsMultimeter Basics

q A Multimeter is used to measure: Voltage

Resistance Continuity (level of resistance)

q When using a Multimeter, youmust properly set it to either ACor DC, depending on the voltageyoure trying to measure.


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CurrentCurrent

qThis is the flow of electrons

which is electricity

qMeasured in amps (a)qAlgebraic Symbol -- I = intensity

qGraphic Symbol A = 1 coulomb/s

A


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VoltageVoltageqThis is the Force or Push of

electricity, aka. Electro-MotiveForce(EMF); amount of work or

energy potential (joules/coulombs)qMeasured in volts (v)

qAlgebraic Symbol -- E or V

qGraphic Symbol~

_

+


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ResistanceResistanceqThis is the property of matter which

opposes the flow of electrons

qMeasured in ohms ( )

qAlgebraic Symbol -- R

qGraphic Symbol


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CapacitanceCapacitance

qThis is the property of matter whichopposes the change in voltage

qMeasured in farads (F)qAlgebraic Symbol is C

q

Graphic Symbol


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Capacitance - contd.Capacitance - contd.

qA capacitor acts like a battery. It is

also a DC filter, depending on the

frequency of the voltage. The

dielectric between plates

determines the flow of electrons

between the plates and the

charging capacity of the device.


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Capacitance-contdCapacitance-contd

qCapacitive reactance resists DC

flow

frequency

Xc Xc = 1/2 C


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InductanceInductance

qThis is the property of matter which

opposes the change in current

qMeasured in henrys (H)

qAlgebraic Symbol is L

qGraphic Symbol


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Inductance-Inductance-contdcontd

qAllows DC, filters AC

q

Electromagnetic

frequency

XL

XL = 2 L Inductive Reactance


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Inductance - contd.Inductance - contd.

qAn inductor acts like an AC filter,

again related to frequency. The

inductance increases as the

frequency increases (which is

inverse to that of capacitances

relationship to frequency).


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PowerPower

qThis is the ability of electricity to

perform work

qMeasured in watts (W)

qAlgebraic Symbol -- P

qNo graphic symbol


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RelationshipsRelationships

qOhm's Law

E = I x R

qPower LawP = I x E

E

I R

P

I E


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Power - contd.Power - contd.

qOhms Law is linear when

temperature is at a constant --

ranges are affected by both low

and high temps. The hotter the

device, the greater the resistance.


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A CircuitA Circuit

q

For electricity to flow, one musthave a complete path.

Complete Circuit

Open Circuit

Short Circuit


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A Circuit - contd.A Circuit - contd.

qWire (a medium for transmission)

qSource (power -- e.g. battery)

qLoad (resistance)

qControl (switch, dial, phone)


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Required PartsRequired Parts

of an Electrical Circuitof an Electrical CircuitSource or Battery Complete Path

Resistance


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CircuitsCircuits

qSeries -- A single path for current to

flow

qParallel -- A single voltage shared

by multiple loads

q

Complex -- Combinations of seriesand parallel


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A Series CircuitA Series Circuit

_

+

R1

R2

R3

EI


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Series Circuit - Total ValueSeries Circuit - Total Value

Rtotal= R1 + R2 + Rn

R1 = 5 , R2 = 15 , and R3 = 7

What is the total resistance of the circuit?


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Simple Parallel CircuitSimple Parallel Circuit

_

+

R1 R2E

I

I1 I2


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Simple Parallel Circuit - contdSimple Parallel Circuit - contd

R1

R2

R1 + R2


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A More Complexed ParallelA More Complexed Parallel

CircuitCircuit

_

+

R1 R2 R3E

I

I3I1 I2


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Complexed Parallel CircuitComplexed Parallel Circuit

1

1/R1 + 1/R2 + + 1/Rn

Total resistance for a complex parallelcircuit.


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A Complex CircuitA Complex Circuit

R2

E_

+

R1

R7

R3 R4 R5

R8

R9I


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DiodesDiodes

qDiodes allow the flow of current

through it in only one direction

Current flow


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Diodes-Diodes-contdcontd

qOther types of diodes Zener

High frequency Light emitting

Photodiodes

Shockley

etc.


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Two Types of CurrentTwo Types of Current

q Alternating Current (AC)electrical

current flows in both directions; positive

and negative terminals continuously

trade places (polarity)

Example: Electricity provided by Vectren

q Direct Current (DC)electrical current

flows in one direction; negative topositive

Example: Electricity provided by batteries


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Alternating VS Direct CurrentAlternating VS Direct Current

qWhy AC?

qWhere AC?

qHow AC to DC?


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Direct Current (DC)Direct Current (DC)

_

+

R1

R2EI

volts

2

4

6

time

E


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Alternating Current (AC)Alternating Current (AC)R1

R2EI

~

volts

2

4

6

time

E

-6

-4

-2

0

E


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Characteristics of ACCharacteristics of ACqAmplitude

Peak

Peak-to-peak

Root Mean Square (RMS)qFrequency/Period

qPhasev

olts

2

4

6

time

E

-6

-4

-2

0

E


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AC to DCAC to DC

q

AC

volts

2

4

6

time

-6

-4

-20

E

REI

~


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AC to DCAC to DC

q

Half Wave

volts

2

4

6

time

-6

-4

-20

E

RE

I

~


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AC to DCAC to DC

q

RC Filter

volts

2

4

6

time

-6

-4

-20

E

RE

I

~


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AC to DCAC to DC

q

Full Wave

volts

2

4

6

time

-6

-4

-20

E

RE

I

~


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AC to DC - contd.AC to DC - contd.

R

~

During positive half-cycle of the input


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AC to DC - contdAC to DC - contd

R

~

During the negative half-cycle of the input


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AC to DCAC to DC

q

Filtered Full Wave

volts

2

4

6

time

-6

-4

-20

E

RE

I

~

RR


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ResonanceResonance

q

Each system has a frequency or set offrequencies that it is in tune with

qTank Circuit

_

+E


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Resonance -Resonance - contdcontd

q In a parallel LC circuit maximum

voltage at the resonant

q In a series LC circuit maximum

current at the resonant


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FiltersFilters

Signal

Po

wer

Frequency

Low Pass

SignalPo

we

r

Frequency

High Pass

Sign

al

Power

FrequencyNotch

Sign

alPowe

r

FrequencyBand Pass


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Filters-Filters-contdcontd

qCapacitor in parallel shorts out highfrequencies

q Inductors in series block high

frequenciesqCapacitors in series allow high

frequencies

q Inductors in parallel allow highfrequencies

I d


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ImpedanceImpedance

qStructure Impedance is the composite AC load

that a circuit or transmission line

presents to the input/output

Treat impedance as resistance

qCommon values

8 , 50 , 75 , 100 ,150 ,300 , 600 , 900 , & 1000

Basics of Electricity 22.10

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