what is an electric charge?

What is an electric What is an electric charge?charge?

An electricAn electric chargecharge is the is the electrical electrical propertyproperty of of matter that matter that creates a creates a forceforce between between objects. objects.

• the the attracting attracting or or repellingrepelling behavior of a behavior of a materialmaterial. .


To create this To create this charge, charge, electrons electrons must must movemove from one from one atom to atom to another.another.


All matter is All matter is made up of made up of atoms.atoms.

Atoms are made Atoms are made up of smaller up of smaller particles particles called called protons, protons, neutronsneutrons and and electronselectrons..

Why do objects become Why do objects become charged?charged? An imbalance of its An imbalance of its

protonsprotons and and electronselectrons occursoccurs Protons Protons positive, positive,

found in the found in the nucleusnucleus

Neutrons Neutrons neutral,neutral, found in the found in the nucleusnucleus

Electrons Electrons negative, negative, orbits the orbits the nucleusnucleus

Conservation of Conservation of ChargeChargeElectrons are bound Electrons are bound

more more tightlytightly to to some atoms and some atoms and molecules than molecules than others. others.

When an electron is When an electron is transferredtransferred, it , it creates an creates an ionion..

Conservation of Conservation of ChargeCharge

A charged atom is an A charged atom is an ionion. . positive ion – atom positive ion – atom

losesloses electrons electrons negative ion – negative ion –

atom atom gainsgains electrons electrons

Charge is always Charge is always conserved – never conserved – never createdcreated or or destroyeddestroyed!!

Conductors and Conductors and InsulatorsInsulators

ELECTRICAL ELECTRICAL CONDUCTORSCONDUCTORS

ConductorsConductors allow allow electronselectrons to to flow flow Conductivity Conductivity

depends upon how depends upon how tightlytightly the atom the atom holds on to its holds on to its electronselectrons..

looseloose electrons in a electrons in a material conduct the material conduct the electric charge electric charge through (metals).through (metals).

Examples of Examples of conductors: Metal, conductors: Metal, graphite, etc.graphite, etc.

In In solidsolid conductors, conductors, the electrons carry the electrons carry the charge through the charge through the circuit because the circuit because

they are they are looselyloosely held. held.

In In fluidsfluids, like those in , like those in a car battery, a car battery, positivepositive

and negative and negative ionsions and and electronselectrons may may

compose the flow of compose the flow of electric charge.electric charge.

ELECTRICAL ELECTRICAL CONDUCTORSCONDUCTORS

ELECTRICAL ELECTRICAL INSULATORSINSULATORSInsulators DO NOTInsulators DO NOT

conduct conduct electricity well!!electricity well!! They provideThey provide RESISTANCE RESISTANCE to the flow to the flow of electrons.of electrons.

RESISTANCERESISTANCE IS CAUSED IS CAUSED BYBY INTERNAL FRICTIONINTERNAL FRICTION

Examples of Insulators: Examples of Insulators: Glass, wood, rubber, etc.Glass, wood, rubber, etc.

SEMICONDUCTORSSEMICONDUCTORS

SemiconductorSemiconductor – – material made material made to behave to behave sometimes as sometimes as insulatorsinsulators and and sometimes as sometimes as conductors conductors ((germaniumgermanium and and siliconsilicon).).

Electric FieldsElectric FieldsAn electric field An electric field

surrounds every surrounds every electricelectric charge and charge and exerts the force that exerts the force that causes other electric causes other electric charges to be charges to be repelledrepelled or or attractedattracted..

Electric fields are Electric fields are represented by represented by arrows that show arrows that show how the electric field how the electric field would make a would make a positivepositive charge charge move.move.

Charges Exert ForcesCharges Exert ForcesCharges Exert Charges Exert

ForcesForces

Unlike charges Unlike charges attractattract each each other (other (positivepositive and and negativenegative))

Like charges Like charges repelrepel each each other (positive other (positive to to positivepositive or or negative to negative to negativenegative))

Charges Exert ForcesCharges Exert ForcesJust like gravity, Just like gravity,

the amount of the amount of electrical electrical force force exerted exerted on an object on an object is related to is related to the following:the following:

1.1. DistanceDistance from from the charged the charged objectobject

2.2. Strength of Strength of thethe charge charge on on the charged the charged objectobject

How can objects How can objects become charged?become charged?

1) Charging by 1) Charging by ContactContact – –

Two objects are Two objects are rubbed against rubbed against each other and each other and electronselectrons are are transferredtransferred..

PROTONS PROTONS NEVER NEVER MOVE from one MOVE from one atom to atom to another.another.


OR, A charged object touches a OR, A charged object touches a neutral object, neutral object, transferringtransferring electrons – electrons –

PROTONSPROTONS NEVER NEVER MOVE from one MOVE from one atom to anotheratom to another


Charging by Charging by InductionInduction (charging at a (charging at a distance) – A distance) – A charged object charged object is held near a is held near a neutral neutral object object and causes an and causes an overall overall charge. charge.

Charge Charge PolarizationPolarizationWhen charges When charges

rearrangerearrange in an in an atom, one side atom, one side becomes slightly becomes slightly more more positivepositive and and the other side the other side becomes slightly becomes slightly more more negativenegative. . The atom is The atom is electrically electrically polarizedpolarized.. Ex – Ex – charged comb charged comb attracting bits of attracting bits of paper or charged paper or charged balloon sticking balloon sticking to the wall.to the wall.

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 differencedifference or or voltage voltage difference difference causes electrons causes electrons to flow in one net to flow in one net directiondirection. .

This voltage This voltage difference difference provides the provides the ““pushpush” or the ” or the ““pressurepressure” to ” to move in a given move in a given direction, and the direction, and the SI unit is SI 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 six Contains six wetwet 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

ResistanceResistance

Temperature, Temperature, LengthLength, and , and thicknessthickness affect affect the amount of the amount of resistance of a resistance of a material.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 thought of as Amperes can be thought 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.


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.


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

V=IRV=IR V= V= VoltageVoltageI= I= Amperage Amperage

(Current)(Current)R= R= ResistanceResistance

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=IVP=IVP=P=powerpowerI=I=AmpereAmpereV= V= VoltageVoltage

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.


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.


For a circuit to For a circuit to allow the flow allow the flow of electrons, it of electrons, it must be must be closedclosed which means which means

that it makes a that it makes a complete complete looploop

back to the back to the powerpower source. source.


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.


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 BREAKERSBREAKERS

How do fuses work?Fuses melt to Fuses melt to

prevent circuit prevent circuit overloads.overloads.

A fuse is a ribbon A fuse is a ribbon of wire with a low of wire with a low melting pointmelting point

How do circuit breakers work?

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

Made of a magnet Made of a magnet or bimetallic stripor bimetallic strip

what is an electric charge?

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