Fox Valley Technical College Appleton, WI Communication Signals Voltage, Current, Resistance 10/1/20151.

Fox Valley Technical College

Appleton, WI

Communication Communication SignalsSignals

Voltage, Current, ResistanceVoltage, Current, Resistance

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ElectricityElectricity

Where does it come from?Where does it come from?

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Electric ChargeElectric Charge

What is it?What is it?

Foundation

• Regardless of the state or form that matter takes, it can be categorized into two groups.

• One group is the element, which may be

divided yet maintain all of its characteristics until only one atom is present (like copper).

• The other group is the compound, which may

be divided yet maintain its characteristics until only one molecule is present (like water).

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The Atom• An atom is an extremely small particle

invisible to the naked eye. The word atom comes from the Greek atomos , meaning indivisible. Only in recent times has sophisticated equipment allowed scientists to see atoms and prove their structure and existence. The characteristics of an atom or element is determined by the number of protons and neutrons found in its center or nucleus.

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Construction of the AtomConstruction of the Atom

Neutron

Proton

Electron

Nucleus

“Shell”

Electrons are orbiting the nucleus at a similar distance from the nucleus, at an energy level called a shell. Each shell has a limited capacity for electrons. Additional electrons go into a higher energy level shell, further from the nucleus. The nth shell may contain up to 2n2 electrons.

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Copper AtomCopper Atom

Shell Electrons

1 2(Full Shell)

2 8(Full Shell)

3 18(Full Shell)

4 1(of 32

possible)

“Valence Shell” = the outermost shell

+29

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AtomsAtoms

Classification for Electrical Materials:

• Conductors– 1 to 3 valence electrons

• Semiconductors– 4 valence electrons

• Insulators– More than 4 valence electrons

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Electric Charges Exert ForceElectric Charges Exert Force(Electric Force Field or (Electric Force Field or

Electromotive Force – EMF - it is Electromotive Force – EMF - it is measured in Volts)measured in Volts)

NO Charge NO Charge NO force NO force

Opposite Charges Opposite Charges Force of Force of AttractionAttraction

Like Charges Like Charges Force of Force of RepulsionRepulsion––

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+–

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+–

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A Stronger Electric Force FieldA Stronger Electric Force Field

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More charges More charges Greater force Greater force More More VoltageVoltage

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Measuring ChargeMeasuring Charge• Two types: Positive and Negative

(random definitions)

• Name for Unit of Measure: “Coulomb”

• Electrons in one Coulomb of negative charge: = 6.25 x 1018 electrons [by definition] (6,250,000,000,000,000,000)

• Charge on one electron: = –1.6 x 10-19 Coulombs (-.00000000000000000016)

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Net Positive Charge of an AtomNet Positive Charge of an Atom

When missing one valence electron, the copper atom has a net Positive charge. Then the copper atom has a force of attraction to another electron.

+29 – 28 = +1

+29

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Net Negative Charge of an AtomNet Negative Charge of an Atom

When having an extra valence electron, the copper atom has a net Negative charge. Then the copper atom has a force of repulsion toward the extra electron.

+29 – 30 = -1

+29

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Voltage

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• A measure of the force that makes charges move

• Sometimes called “potential”

• Also called “Electromotive Force” or “EMF”

• Symbol: V

• Unit of Measure: Volt

• Can be stored like air in a balloon

VoltageVoltage

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General Definition: The amount of energy per unit of charge required to move a quantity of charge between two points.

VoltageVoltage

One volt of electric field force is required when expending one joule of energy in the process of moving one Coulomb of charge from one point to another.

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W joules

V VoltsQ coulombs

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−−−

−−−−−−−

−−−−− ++++ ++++ ++++ ++++ ++

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Held in position Movable

OneCoulomb

Electric Field ForceOf One Volt

One joule of energy is expended in moving one coulomb of charge from its initial to its final position.

Voltage SourcesVoltage Sources

Regenerative Voltage Sources:

• Chemical: Batteries – (Rated in Amp-Hours of life)

• Mechanical: Generators– (Rated in kilowatts)

• Photo-voltaic: Solar Cells– (On a bright, sunny day, the sun provides

approximately 1,000 watts of energy per square meter)

• Converters: Electronic Power Supplies– Convert AC to DC voltage and current

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Non-Regenerative Sources:

• Capacitors– Their voltage declines with use.

Cells and Batteries

• A battery is used to convert chemical energy into electricity. Sometimes, a flashlight cell is incorrectly referred to as a battery. A cell is a single voltage producing unit, whereas the battery is a group of cells that are connected so the output can be maximized. An automobile battery is made up of six individual cells resulting in a total output of 12.6 volts.

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Voltage Sources - CellVoltage Sources - Cell

Electrolytic Chemical

Positive Electrode Negative Electrode

Battery Constructed of multiple Cells

(Anode) (Cathode)

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Voltage Sources - BatteriesVoltage Sources - Batteries

Battery operation:

• Chemical interaction between the electrolyte and the electrodes.– Causes a continuous supply of electrons at

the negative electrode.– Causes a shortage of electrons at the

positive electrode.

• Eventually, the chemicals are depleted.– In some batteries, the chemical action can

be reversed, “recharging” the battery.

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Two types of Chemical Cells

• Primary Cells– An alkaline cell is a primary cell which destroys itself

in the process of creating an EMF.– Zinc-carbon, alkaline, mercury, silver oxide and

lithium are examples of primary cells.

• Secondary Cells– found in the auto battery (lead acid) or the nicad cell

found in many portable telephones, are rechargeable and my be reused many times.

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Voltage Sources - BatteriesVoltage Sources - Batteries

+ – + – + –+ –

The voltages or potentials add.

The current capability is the same as one battery.

Batteries connected in SERIES

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Voltage Sources - BatteriesVoltage Sources - Batteries

+ –

+ –

+ –

+ –

The voltage or potential is the same as one battery.

The current capabilities add.

Batteries connected in PARALLEL

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Voltage SourcesVoltage SourcesSolar (Photovoltaic) CellsSolar (Photovoltaic) Cells

•Made of semiconductor materials. Doped silicon is the most commonly used material.

•When light strikes the material, a portion of the light is absorbed, imparting energy to valence shell electrons and allowing them to move more freely.

•The light also produces electric fields that induce electrons freed by light absorption to move in one direction.

• It's only fuel requirement is light and it leaves no pollution. Solar energy is used to power most satellites that orbit the earth.

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Current

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CurrentCurrent

•The continuous movement of charge over time

•The rate of flow of charge

•Symbol: I

•Unit of Measure: Ampere

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CurrentCurrent

General Definition:

The number of charges flowing through a

cross sectional area per unit of time.

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( )

( )( )

Q coulombsI Amperes

t seconds

One ampere flows when one Coulomb of charge moves through a given cross-sectional area in one second.

CurrentCurrent

Without voltage applied, free electrons in a conductor or semiconductor move at random.

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CurrentCurrent

Free electrons under pressure to move.

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CurrentCurrent

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As each electron vacates a valence shell, it leaves a hole that can be filled by another moving electron.

If electrons are forced to flow in one direction, their vacated holes appear to flow in the opposite direction.

HoleElectron

Current - Rate of FlowCurrent - Rate of Flow

Unit: One ampere flows when one Coulomb of charge moves through a cross-sectional area in one second.

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CurrentCurrent

Hole Flow (+ to -)(“Conventional” Flow)

Electron Flow (- to +)

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Voltage - Current ConventionVoltage - Current ConventionConventional Current Flow

I +

V

−

Passive ComponentsVoltage Sources

I

VS

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Voltage - Current Voltage - Current ConventionConvention

ElectronElectron Current Flow Current Flow

I

+

V

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Passive ComponentsVoltage Sources

I

VS

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Resistance

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ResistanceResistance

• A measure of the opposition to current flow in a given material.

• Symbol: R

• Unit of Measure: Ohms

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ResistanceResistance

Definition:

The property of different materials to restrict electron flow differently.

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V IR

One ohm (Ω) of resistance occurs when one volt of potential is applied and one ampere of current flows.

Resistor SymbolResistor Symbol

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Copper wire resistance table

 AWG Feet/Ohm Ohms/100ft Ampacity*   10 490.2 .204 30

12 308.7 .324 20

14 193.8 .516 15

16 122.3 .818 10

18 76.8 1.30 5

20 48.1 2.08 3.3

22 30.3 3.30 2.1

24 19.1 5.24 1.3

26 12.0 8.32 0.8

28 7.55 13.20 0.5

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Resistance vs. ImpedanceResistance vs. Impedance

We use two different words to describe the fact that a given material or device will let electrons flow just so fast at a given voltage:

We reserve the term “Resistance” for purely resistive components used in DC and AC circuits.

We reserve the term “Impedance” for other types of components in AC circuits.

Impedance is a topic reserved for more advanced studies in electronics.

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