Electric Electric Charges & Charges &

CurrentCurrent

Chapter Chapter 77

Types of electric chargeTypes of electric charge ProtonsProtons w/ ‘w/ ‘++’ charge “’ charge “stuckstuck” in ” in

the nucleusthe nucleus ElectronsElectrons w/ ‘w/ ‘--’ charge ’ charge freely freely

moving moving around the nucleus in around the nucleus in orbitsorbits

ConductorsConductors Allow the Allow the easy flow easy flow of electricityof electricity loosely bound electrons loosely bound electrons that are free that are free

to move from atom to atomto move from atom to atom metalsmetals like aluminum, gold, copper like aluminum, gold, copper

and silver and silver

InsulatorsInsulators InsulatorsInsulators – – resists the flow resists the flow of electronsof electrons

hold more tightly to their valence hold more tightly to their valence electrons: electrons:

plastic, rubber, glassplastic, rubber, glass

Interactions between Interactions between chargescharges same as in magnetismsame as in magnetism

Unlike magnetism were on a magnet Unlike magnetism were on a magnet there is always a + on one end and a – there is always a + on one end and a – on the other end of the magneton the other end of the magnet

electrical charges can electrical charges can exist aloneexist alone Like charge repelLike charge repel Opposite charges attractOpposite charges attract

Electric FieldsElectric Fields Exert a force through the force field in all Exert a force through the force field in all

directions from the charged particledirections from the charged particle When a charged particle enters the force field of When a charged particle enters the force field of

another particle it is either another particle it is either attracted or repelledattracted or repelled The diagram represents The diagram represents stronger force stronger force as the lines as the lines

get get closer & closer togethercloser & closer together

Static ChargeStatic Charge Latin word “Latin word “StasisStasis” which means “” which means “StaysStays”” Objects are typically “Objects are typically “Neutral” w/ the same # of protons and Neutral” w/ the same # of protons and

electronselectrons They can become “They can become “chargedcharged” by ” by gaininggaining or or losinglosing electronselectrons – –

NOT PROTONSNOT PROTONS! – They stay in the nucleus!! – They stay in the nucleus! The The buildupbuildup of these charges is “ of these charges is “Static ElectricityStatic Electricity”” In In Static Electricity Static Electricity the charges the charges build up and build up and STAYSTAY; ;

they don’t flow as they do in they don’t flow as they do in electric currentselectric currents

TransferringTransferring Static Static ChargeCharge FrictionFriction – transferred from rubbing i.e. get shocked after – transferred from rubbing i.e. get shocked after

walking on the walking on the carpetcarpet ConductionConduction – transferred by direct contact w/ another – transferred by direct contact w/ another

object – hair object – hair standing on end w/ standing on end w/ Van de Graff machineVan de Graff machine InductionInduction – the force field of a highly negatively charged – the force field of a highly negatively charged

object pushes the object pushes the electrons away from nearby objects causing electrons away from nearby objects causing them to become + charged, they then are attracted to each other. them to become + charged, they then are attracted to each other. i.e. statically charged balloon attracts small pieces of torn up i.e. statically charged balloon attracts small pieces of torn up paperpaper

Static DischargeStatic Discharge Objects don’t hold a static charge forever – Objects don’t hold a static charge forever – objects tend toward objects tend toward

equilibriumequilibrium – – they “want” to be neutralthey “want” to be neutral When electrons move toward this equilibrium – static discharge occursWhen electrons move toward this equilibrium – static discharge occurs

HumidityHumidity – – water (a polar molecule) vapor in the air pulls electrons off negatively water (a polar molecule) vapor in the air pulls electrons off negatively charged objects, preventing static charges to build upcharged objects, preventing static charges to build up

Sparks & Lightning Sparks & Lightning - - objects reaching static equilibriumobjects reaching static equilibrium

Circuit MeasurementsCircuit Measurements Electric Current Electric Current - - Flow of electrons through a Flow of electrons through a

materialmaterial Electrical Potential Electrical Potential – –

Similar to potential energy (lifting something higher Similar to potential energy (lifting something higher against the force of gravity gives it greater against the force of gravity gives it greater potential to potential to do workdo work, increasing its potential energy.), increasing its potential energy.)

When given the opportunity, objects will move from When given the opportunity, objects will move from higher potential energy to an area of lower potential higher potential energy to an area of lower potential energyenergy

Electrical potential is related to their electrical fields and Electrical potential is related to their electrical fields and not to height – not to height – as electrons build up on one side they as electrons build up on one side they “want” to flow to an area w/ less potential“want” to flow to an area w/ less potential

VoltageVoltage VoltageVoltage – causes current to flow through an electrical circuit– causes current to flow through an electrical circuit VoltVolt – unit of measure to measure this potential– unit of measure to measure this potential A A Voltage Source Voltage Source ((batterybattery or or generatorgenerator) is required to maintain ) is required to maintain

the electrical potential in a circuit.the electrical potential in a circuit.

Electrical CurrentElectrical Current Water flowing thru a pipe depends on more than the angle Water flowing thru a pipe depends on more than the angle

of the pipe. It also depends on the length of the pipe, of the pipe. It also depends on the length of the pipe, diameter of the pipe and if the pipe is clogged or open.diameter of the pipe and if the pipe is clogged or open.

Electrical Current Electrical Current is measured in is measured in AmperesAmperes Amount of Electrical Current ( amps) depends on more Amount of Electrical Current ( amps) depends on more

than just Voltage, it depends on the Resistance found in than just Voltage, it depends on the Resistance found in the circuit.the circuit.

Electrical ResistanceElectrical Resistance the the oppositionopposition to the flow of electricity – to the flow of electricity – measured in measured in OhmsOhms – symbol is the – symbol is the Greek letter Omega Greek letter Omega -- Water flowing thru a pipe depends on more than the angle Water flowing thru a pipe depends on more than the angle

of the pipe. It also depends on the length of the pipe, of the pipe. It also depends on the length of the pipe, diameter of the pipe and if the pipe is clogged or open.diameter of the pipe and if the pipe is clogged or open.

Electricity will take the Electricity will take the path of least resistancepath of least resistance The The greater the resistance, the less current greater the resistance, the less current there is for a there is for a

given voltage.given voltage. a. a. Longer wires Longer wires have have greater resistance greater resistance than short wiresthan short wires b. b. Thin wires Thin wires have have more resistance more resistance than thick wirethan thick wire c. High conductors have less resistance than insulatorsc. High conductors have less resistance than insulators

Series CircuitsSeries Circuits Series Circuits Series Circuits – provides – provides only one path only one path for the for the

electrons to followelectrons to follow 1. A break in the circuit stops the flow of electricity to all other 1. A break in the circuit stops the flow of electricity to all other

parts of the circuitparts of the circuit 2. With multiple light bulbs (more resistance) the current 2. With multiple light bulbs (more resistance) the current

reduces & the dimmer the lights becomereduces & the dimmer the lights become 3. 3. Ammeters Ammeters should be wired in seriesshould be wired in series

Parallel CircuitsParallel Circuits Parallel circuits Parallel circuits – the different parts of the circuit are on – the different parts of the circuit are on

separate branchesseparate branches A break (burn out light bulb) in the circuit doesn’t stop the A break (burn out light bulb) in the circuit doesn’t stop the

flow to the remaining devicesflow to the remaining devices Multiple light bulbs will remain the same brightness since Multiple light bulbs will remain the same brightness since

the resistance is not decreasing as it does in a series the resistance is not decreasing as it does in a series circuit.circuit.

Each pathway can be separately switched off w/out Each pathway can be separately switched off w/out affecting the othersaffecting the others

Household circuits – Wired in parallelHousehold circuits – Wired in parallel, with a standard of , with a standard of 120 volts120 volts

Voltmeters are wired in parallelVoltmeters are wired in parallel

Parallel CircuitsParallel Circuits The The more paths the LESS the resistancemore paths the LESS the resistance

Water example again: added pipes coming from Water example again: added pipes coming from a large tank will allow more water to flow out a large tank will allow more water to flow out that a single pipe.that a single pipe.

Therefore Therefore as resistance degreases, current as resistance degreases, current increases; they are inversely proportionalincreases; they are inversely proportional

Schematic DiagramsSchematic Diagrams All circuits need at least the followingAll circuits need at least the following

Power supply, wire, resistors, other items include Power supply, wire, resistors, other items include switches, connectors, meters, etc. switches, connectors, meters, etc.

There is a set of standard symbols used to There is a set of standard symbols used to represent these items in a diagram of the circuitrepresent these items in a diagram of the circuit

Batteries -Batteries -Electrochemical Electrochemical cellscells 1. 1. Converts chemical energy into electrical energyConverts chemical energy into electrical energy

2. Consists of two different metals – the 2. Consists of two different metals – the electrodeselectrodes 3. Electrodes immersed in a chemical “bath” that conducts 3. Electrodes immersed in a chemical “bath” that conducts

electricity called the electricity called the electrolyteelectrolyte 4. The part of the electrodes above the electrolyte is the 4. The part of the electrodes above the electrolyte is the

terminalterminal and used to connect the battery to the circuit. and used to connect the battery to the circuit.There is a chemical reaction between the electrodes and the electrolyte resulting ina buildup of electrons on one of the terminals (it becomes the “-“ terminal)The other terminal gives up its electrons and becomes the “+” terminal.This difference sets up the electrical potential of the system = VoltsWhen cells are connected in series the voltages of the cells are added together

Dry cell & Wet cellDry cell & Wet cell Wet Cell Wet Cell – the electrolyte is a liquid (car battery)– the electrolyte is a liquid (car battery)

i. In a car battery, Electrolyte is sulfuric acid the “+” terminal i. In a car battery, Electrolyte is sulfuric acid the “+” terminal is lead oxide and the “-“ terminal is lead metalis lead oxide and the “-“ terminal is lead metal

Dry Cell Dry Cell – the electrolyte is not really dry; but is a paste– the electrolyte is not really dry; but is a paste i. Standard AA, C, D type batteries, electrolyte is a paste. The i. Standard AA, C, D type batteries, electrolyte is a paste. The

“+” terminal is“+” terminal is

That’s all That’s all