ELECTRIC CURRENTELECTRIC CURRENT

What is current What is current electricity?electricity?CurrentCurrent Electricity - Flow of Electricity - Flow of

electronselectrons

What causes electrons to flow?What causes electrons to flow?

When an electric When an electric force force is is applied, it causes a applied, it causes a potential potential difference or difference in difference or difference in voltagevoltage between the ends of between the ends of a a conductorconductor. .

When there is no potential When there is no potential differencedifference, the flow of charge , the flow of charge stopsstops..

Direct Current and Direct Current and Alternating CurrentAlternating Current

DirectDirect Current Current – flow of charge – flow of charge always flows in one always flows in one directiondirection. . Batteries use DC to flow from Batteries use DC to flow from the the negative negative terminal to the terminal to the positivepositive terminal. terminal.

AlternatingAlternating Current Current – electrons – electrons move move backback and and forthforth about about relatively fixed positions. relatively fixed positions. Power utilities use AC. AC Power utilities use AC. AC allows low-cost, high voltage allows low-cost, high voltage energy transmission across energy transmission across great great distancesdistances, with safe low-, with safe low-voltage use by the voltage use by the consumerconsumer. .

PotentialPotential difference difference or or voltage voltage difference causes difference causes electrons to electrons to flowflow in one net in one net direction. direction.

This voltage difference This voltage difference provides the “provides the “pushpush” or the ” or the ““pressurepressure” to move in a ” to move in a given direction, and the SI given direction, and the SI unit is unit is VoltageVoltage (volts) (volts)

Voltage SourcesVoltage SourcesVoltage sourcesVoltage sources: :

drydry cell cell batteries, batteries, wetwet cell batteries, cell batteries, lead- acidlead- acid batteries and batteries and generatorsgenerators. .

They supply the They supply the energy or the energy or the ““pushpush” to allow ” to allow the charges to the charges to movemove. .

Voltage SourcesVoltage SourcesDry Cell BatteriesDry Cell Batteries Consists of two Consists of two

electrodes electrodes surrounded by an surrounded by an electrolyteelectrolyte..

In the dry cell In the dry cell shown here, one shown here, one electrode is the electrode is the carboncarbon rod and rod and the other is the the other is the zinc zinc container.container.

Voltage SourcesVoltage SourcesWet Cell BatteriesWet Cell Batteries Contains two Contains two

connected connected platesplates made of different made of different metalsmetals in a in a conducting conducting solutionsolution..

Voltage SourcesVoltage Sources

Lead-Acid BatteriesLead-Acid Batteries Most Most carcar batteries batteries

are are lead-acidlead-acid batteries.batteries.

Contains Contains sixsix wet wet cells made of cells made of leadlead and lead dioxide and lead dioxide plates in a plates in a sulfuricsulfuric acid solution.acid solution.

Voltage SourcesVoltage SourcesIn dry and wet cell In dry and wet cell

batteries, a batteries, a chemical chemical reaction reaction occurs releasing occurs releasing energyenergy inside the inside the cell which is then cell which is then converted to converted to electrical electrical energy. energy.

Generators, like the Generators, like the alternatorsalternators in in vehicles, convert vehicles, convert mechanical mechanical energy energy to to electrical electrical energy.energy.

ResistanceResistanceResistanceResistance is is

the tendency the tendency of a material to of a material to opposeoppose the the flow of flow of electronselectrons, , changing changing electrical electrical energy into energy into thermalthermal energy energy andand light light..

ResistanceResistanceAlmost all Almost all

materials materials have have some electrical some electrical resistanceresistance..

ConductorsConductors have less have less resistance resistance than than insulators.insulators.

The The SI unitSI unit for for resistance isresistance is

ResistanceResistanceTemperature, Temperature,

LengthLength, and , and thicknessthickness affect the affect the amount of amount of resistance of resistance of a material.a material.

ResistanceResistance increases as increases as temperature temperature increases.increases.

ResistanceResistance

Resistance Resistance increasesincreases as as wire becomes wire becomes longer longer or as or as the gauge the gauge (diameter) (diameter) becomes becomes thinnerthinner..

Electric Electric currentcurrent is the flow is the flow of electric of electric chargecharge and is and is

measured in measured in amperesamperes (amps).(amps).

Amperes can be though of as Amperes can be though of as the the volumevolume of current of current

running through a running through a circuitcircuit..

Current in a Simple Current in a Simple CircuitCircuit

A simple circuit A simple circuit contains:contains:

1)A voltage 1)A voltage sourcesource

2)A 2)A resistorresistor (such (such as a light bulb)as a light bulb)

3)Conductors 3)Conductors that connect the that connect the devicedevice to the to the voltagevoltage source. source.

Current in a Simple Current in a Simple CircuitCircuit

VoltageVoltage, , currentcurrent, and , and resistanceresistance in a in a simple circuit simple circuit are related.are related.

This This relationship is relationship is known as known as Ohm’sOhm’s law. law.

Current in a Simple Current in a Simple CircuitCircuit

Ohm’s Law Ohm’s Law can be can be written as:written as:

V=IRV=IR V= V= VoltageVoltageI= I= AmperageAmperageR= R= ResistanceResistance

ELECTRICAL ENERGYELECTRICAL ENERGY

SERIES AND PARALLEL SERIES AND PARALLEL CIRCUITSCIRCUITS

What is a What is a series circuit?series circuit?

A A series series circuit circuit has only has only one one

path for path for current.current.

SERIES AND PARALLEL SERIES AND PARALLEL CIRCUITSCIRCUITS

What is a What is a parallel parallel circuit?circuit?

AA parallel parallel circuit has circuit has

multiple multiple paths paths for current.for current.

SERIES AND PARALLEL SERIES AND PARALLEL CIRCUITSCIRCUITS

For a circuit to For a circuit to allow the flow of allow the flow of

electrons, it electrons, it must be must be closedclosed which means which means

that it makes an that it makes an complete complete looploop

back to the back to the powerpower source. source.

SERIES AND PARALLEL SERIES AND PARALLEL CIRCUITSCIRCUITS

If it is If it is openopen, , the path that the path that electrons can electrons can

follow is follow is broken broken and and the resistor the resistor

will not work.will not work.

SERIES AND PARALLEL SERIES AND PARALLEL CIRCUITSCIRCUITS

If there is a If there is a shortshort circuit, circuit, the resistor will not the resistor will not workwork, even though there , even though there is a complete is a complete pathpath..

The reason is because The reason is because electricityelectricity will always will always follow the path of least follow the path of least resistanceresistance and will and will therefore not travel therefore not travel through the resistor.through the resistor.

SCHEMATIC DIAGRAMSSCHEMATIC DIAGRAMS

Schematic Schematic DiagramsDiagrams are used to are used to represent represent circuitscircuits..

FUSES AND CIRCUIT FUSES AND CIRCUIT BREAKERSBREAKERSHow do fuses work?

Fuses melt to prevent circuit overloads.Fuses melt to prevent circuit overloads. A fuse is a ribbon of wire with a low A fuse is a ribbon of wire with a low

melting pointmelting point

How do circuit breakers work?

Circuit breakers open circuits Circuit breakers open circuits with high current.with high current.

Made of a magnet or bimetallic Made of a magnet or bimetallic stripstrip

Electrical PowerElectrical Power

Electrical Power Electrical Power is the is the raterate at at

which which electricalelectrical energy is energy is

converted into converted into another form of another form of energyenergy, and can , and can be written as:be written as:

P=IRP=IRP=P=powerpowerI=I=AmpereAmpere

R=R=ResistanceResistance