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General Physical General Physical
ScienceScience
Chapter 8Chapter 8
Electricity and MagnetismElectricity and Magnetism
Electrical ChargeElectrical Charge
Electrical charge is one of the 7 Electrical charge is one of the 7
fundamental quantities.fundamental quantities.
Two types of electrical chargeTwo types of electrical charge
–– Positive (+)Positive (+)
––Negative (Negative (--))
–– 3 types of sub3 types of sub--atomic particlesatomic particles
Protons (+)Protons (+)
Electrons (Electrons (--))
Neutrons (no charge)Neutrons (no charge)
Electrical ChargeElectrical Charge
The magnitude of the proton charge The magnitude of the proton charge
is equal to the magnitude of the is equal to the magnitude of the
electron charge.electron charge.
––Charges will exactly cancel.Charges will exactly cancel.
CoulombCoulomb
––Unit of electrical chargeUnit of electrical charge
––+q = greater + charge = electron +q = greater + charge = electron
deficientdeficient
–– --q = greater q = greater -- charge = electron richcharge = electron rich
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Electrical ForceElectrical Force
Exists between two charged particlesExists between two charged particles
Law of chargesLaw of charges–– Unlike charges attract and like charges Unlike charges attract and like charges
repel.repel.
Magnitude of the force = CoulombMagnitude of the force = Coulomb’’s s LawLaw–– The force of attraction or repulsion between The force of attraction or repulsion between
two charged bodies is directly proportional two charged bodies is directly proportional to the product of the two charges and to the product of the two charges and inversely proportional to the square of the inversely proportional to the square of the distance between them. distance between them.
CoulombCoulomb’’s Laws Law
Mathematically F = kqMathematically F = kq11qq22 / r/ r22
–– F = Force (N)F = Force (N)
–– k = proportionality constantk = proportionality constant9.0 x 109.0 x 1099 N mN m22 / C/ C22
Similar to gravitational law, Similar to gravitational law, howeverhowever……
––Much higher value for the constant.Much higher value for the constant.
–– Based on charges, not masses.Based on charges, not masses.
–– can be an attraction or repulsioncan be an attraction or repulsion
Static ChargeStatic Charge
Excess or deficiency of electronsExcess or deficiency of electrons–– Excess; negative chargeExcess; negative charge
–– DefiencyDefiency; positive charge; positive charge
Walk across carpet in winterWalk across carpet in winter
PolarizationPolarization–– separation of chargeseparation of charge
–– rubbing rubber balloon in hairrubbing rubber balloon in hair
Induced polarizationInduced polarization–– A charge causes charge separationA charge causes charge separation
–– reason balloon sticks to wallreason balloon sticks to wall
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PhotocopierPhotocopier
Se drum + chargeSe drum + charge
Light reflected off paper Light reflected off paper removes some of the removes some of the drum chargedrum charge
Toner has a Toner has a -- chargecharge–– sticks to + areas on sticks to + areas on
drumdrum
Paper + charge gets Paper + charge gets toner from drumtoner from drum
Toner Toner ‘‘fusedfused’’ by heatby heat
Electrical Charge and Electrical Electrical Charge and Electrical
ForceForce
Learning GoalsLearning Goals
––Describe electrical charge in terms of Describe electrical charge in terms of
protons and electronsprotons and electrons
–– State similarities and differences State similarities and differences
between Newtonbetween Newton’’s Law of Universal s Law of Universal
Gravitation and CoulombGravitation and Coulomb’’s Laws Law
Questions: 1Questions: 1--44
Problems: 1, 3Problems: 1, 3
Electrical CurrentElectrical Current
CurrentCurrent
––Rate of flow of electrical chargeRate of flow of electrical charge
––Measured in Amperes (A)Measured in Amperes (A)
1 A = 1C / 1s1 A = 1C / 1s
General: I = q / tGeneral: I = q / t
–– I=CurrentI=Current
–– q=chargeq=charge
–– t=timet=time
q = I x tq = I x t
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CurrentCurrent
ConductorsConductors
–– current flows readilycurrent flows readily
Does not Does not ‘‘flowflow’’ in the traditional sensein the traditional sense
––metals are good electrical conductorsmetals are good electrical conductors
–– ‘‘looseloose’’ electronselectrons
Also reason for good thermal conductivityAlso reason for good thermal conductivity
InsulatorsInsulators
–– current d/n flowcurrent d/n flow
–– electrical wire coatingelectrical wire coating
CurrentCurrent
SemiconductorsSemiconductors
–– intermediate between conductor and intermediate between conductor and
insulatorinsulator
–– allows some (but not free) current flowallows some (but not free) current flow
–– graphite (resistors)graphite (resistors)
–– Silicon/Germanium mixturesSilicon/Germanium mixtures
computer chipscomputer chips
the the ‘‘semiconductorsemiconductor’’ industryindustry
ExampleExample
A current of 0.50 A flows in a wire A current of 0.50 A flows in a wire
for 2.0 minutes. (a) How much (net) for 2.0 minutes. (a) How much (net)
charge goes past a point in the wire charge goes past a point in the wire
in this time? (b) How many in this time? (b) How many
electrons make up this charge?electrons make up this charge?
What do we know?What do we know?
–– a) 0.50 A (C/s), 2.0 min (120 s); q = I a) 0.50 A (C/s), 2.0 min (120 s); q = I
x tx t
–– q = 0.50 C/s x 120 s = 60Cq = 0.50 C/s x 120 s = 60C
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ExampleExample
60 C60 C
Charge on a single electron is 1.6 x Charge on a single electron is 1.6 x
1010--1919CC
How many electrons = 60 CHow many electrons = 60 C
–– 60 C = x(1.6 x 1060 C = x(1.6 x 10--1919C)C)
–– x = 60 C / 1.6 x 10x = 60 C / 1.6 x 10--1919CC
–– x = 3.8 x 10x = 3.8 x 102020 electronselectrons
–– 380,000,000,000,000,000,000 380,000,000,000,000,000,000
electrons!electrons!
VoltageVoltage
Greater separation Greater separation of charges means of charges means more work more work required to required to separate more separate more charges.charges.
Electrical potential Electrical potential energyenergy–– Voltage (potential)Voltage (potential)
–– Work per unit Work per unit chargecharge
–– PE per unit chargePE per unit charge
VoltageVoltage
Measure of electrical potential is the Measure of electrical potential is the volt. (Work per unit charge)volt. (Work per unit charge)
–– 1 V = 1 J / 1 C1 V = 1 J / 1 C
Measurement of the Measurement of the ‘‘frictionfriction’’ for for electrical current flow is called electrical current flow is called resistance.resistance.–– Ohm Ohm -- ΩΩ
Ohms Law Ohms Law -- relationship between relationship between voltage, current, and resistancevoltage, current, and resistance
–– V = IRV = IR
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Current FlowCurrent Flow
Voltage Voltage -- water pressure; Current = water pressure; Current =
water flow; Resistance = water water flow; Resistance = water
wheelwheel
Current FlowCurrent Flow
You must have a complete circuit for You must have a complete circuit for
electricity to flowelectricity to flow
By convention, current flow is the By convention, current flow is the
way that positive charges would way that positive charges would
flow.flow.
–– convention was developed before our convention was developed before our
understanding of protons and neutrons.understanding of protons and neutrons.
––No practical difference because of this No practical difference because of this
convention.convention.
Electrical PowerElectrical Power
Power = current x voltagePower = current x voltage
–– P = IVP = IVBut V = IRBut V = IR
–– P = IP = I22RR
Heat lossHeat loss
–– All metals have some resistanceAll metals have some resistanceLight bulbs (watts)Light bulbs (watts)
–– Lower T, lower resistanceLower T, lower resistance
–– Superconductivity at very low Superconductivity at very low temperatures.temperatures.
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ExampleExample
Find the current and resistance of a Find the current and resistance of a 60W, 120V light bulb in operation.60W, 120V light bulb in operation.
What do we know?What do we know?
–– Power = 60W, Voltage = 120 VPower = 60W, Voltage = 120 V
–– P = IV means 60 = I x 120P = IV means 60 = I x 120
–– I = 60/120 = 0.50 AI = 60/120 = 0.50 A
–– P = IP = I22R means 60 = 0.50R means 60 = 0.5022 x x ΩΩ
–– ΩΩ = 60 / 0.50= 60 / 0.5022 = 240= 240ΩΩ
Current, Voltage and Electrical Current, Voltage and Electrical
PowerPower
Learning GoalsLearning Goals
––Define Define currentcurrent..
––Define Define voltagevoltage, and state how Ohm, and state how Ohm’’s s
law relates it to current and resistance.law relates it to current and resistance.
–– Explain electrical power and identify the Explain electrical power and identify the
parameters used to describe it.parameters used to describe it.
Questions: 5Questions: 5--88
Exercises: 5Exercises: 5--23 odd 23 odd
Simple Electrical CircuitsSimple Electrical Circuits
Two types of currentTwo types of current
––Direct (battery)Direct (battery)
–– Alternating (wall outlet)Alternating (wall outlet)
US ac typically 60 HzUS ac typically 60 Hz
Two basic types of electrical circuitsTwo basic types of electrical circuits
–– SeriesSeries
–– ParallelParallel
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Series CircuitSeries Circuit
Hooked up as a Hooked up as a
chainchain
–– Same current at all Same current at all
points.points.
–– Total resistance Total resistance
sum of individual sum of individual
resistances.resistances.
–– Total voltage drop Total voltage drop sum of individual sum of individual
drops.drops.
–– RRtt = = ΣΣRRii
Parallel CircuitParallel Circuit
Hooked up like a Hooked up like a
rope.rope.
–– Voltage across each Voltage across each
resistance the resistance the
same.same.
–– Current will vary in Current will vary in
each branch.each branch.
–– 1/R1/Rtt = = ΣΣ(1/R(1/Rii))
–– For two resistors:For two resistors:
RRtt= (R= (R11RR22) / (R) / (R11+R+R22))
ExampleExample
Three resistors have values of 6.0Three resistors have values of 6.0Ω, Ω,
6.0Ω, 6.0Ω, and 3.0and 3.0Ω. Ω. What is their total What is their total resistance when connected in parallel, resistance when connected in parallel, and how much current will be drawn and how much current will be drawn from a 12V battery if it is connected to from a 12V battery if it is connected to the circuit?the circuit?
What do we know?What do we know?–– 6.06.0Ω, 6.0Ω, Ω, 6.0Ω, and 3.0and 3.0ΩΩ
–– 1/R1/Rtt=1/R=1/R11 + 1/R+ 1/R22 + 1/R+ 1/R33 = 1/6 + 1/6 + 1/3 = 1/6 + 1/6 + 1/3 = 2/3= 2/3
–– RRtt = 3/2= 3/2ΩΩ
–– V = IR means I=V/R = 12/1.5 = 8.0AV = IR means I=V/R = 12/1.5 = 8.0A
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Parallel CircuitsParallel Circuits
Total resistance Total resistance
always less than always less than
the lowest the lowest
resistanceresistance
Household wiringHousehold wiring
–– all in parallelall in parallel
–– rest will work if one rest will work if one
failsfails
–– Christmas lightsChristmas lights
‘‘Shunt resistorShunt resistor’’
Electrical SafetyElectrical Safety
FusesFuses
–– Edison baseEdison base
end similar to end similar to lightbulblightbulb
can switch fuse ratingscan switch fuse ratings
–– TypeType--SS
bases differentbases different
cannot switch fuse ratingscannot switch fuse ratings
––Circuit breakersCircuit breakers
–– Fuses/CB always on Fuses/CB always on ‘‘hothot’’ sideside
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ElectricalElectrical
Safety Safety Case groundingCase grounding
–– ‘‘33rdrd’’ wirewire
Polarized PlugPolarized Plug
Simple Electrical Circuits and Simple Electrical Circuits and
Electrical SafetyElectrical Safety Learning GoalsLearning Goals
––Define Define voltagevoltage and state how Ohmand state how Ohm’’s s
Law relates it to current and resistanceLaw relates it to current and resistance
–– Explain electrical power and identify the Explain electrical power and identify the
parameters used to describe it.parameters used to describe it.
Questions: 9Questions: 9--1313
MagnetismMagnetism
LodestonesLodestones
–– 66thth Century BCCentury BC
––MagicMagic
Artificial MagnetsArtificial Magnets
––ChineseChinese
––Made from natural magnetsMade from natural magnets
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MagnetismMagnetism
Two regions of magnetic strengthTwo regions of magnetic strength
––North pole (N) points northNorth pole (N) points north
–– South pole (S) points southSouth pole (S) points south
Law of PolesLaw of Poles
–– Like poles repel and unlike poles attract.Like poles repel and unlike poles attract.
–– Attraction/repulsion inversely related to Attraction/repulsion inversely related to
the square of the distance between the the square of the distance between the
poles.poles.
MagnetismMagnetism
All magnets contain both N and S All magnets contain both N and S
polepole
––DipolesDipoles
Magnetic fieldMagnetic field
–– Imaginary lines indicating the direction Imaginary lines indicating the direction
a compass would point if it were placed a compass would point if it were placed
near a magnet.near a magnet.
–– Lines of forceLines of force
MagnetismMagnetism
Use metal filings to Use metal filings to
‘‘seesee’’ magnetic magnetic
field.field.
–– iron filings become iron filings become
magnetizedmagnetized
induced magnetisminduced magnetism
ScrewdriversScrewdrivers
–– serve to show lines serve to show lines
of force.of force.
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MagnetismMagnetism
Source of magnetism is Source of magnetism is
moving/spinning electrons!moving/spinning electrons!
––Can generate magnetic field with Can generate magnetic field with
moving electric fieldmoving electric field
Strength directly proportional to currentStrength directly proportional to current
–– ElectromagnetsElectromagnets
Electromagnetic FieldsElectromagnetic Fields
MagnetismMagnetism
Ferromagnetic Ferromagnetic materialsmaterials–– internal magnetic internal magnetic
domainsdomains
–– Random Random arrangement means arrangement means nonnon--magneticmagnetic
–– Can induce Can induce alignment with alignment with external magnetexternal magnet Tends to randomize Tends to randomize
with removal of with removal of external magnet.external magnet.
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MagnetsMagnets
–– ‘‘SoftSoft’’ iron iron --temporary temporary
magnetismmagnetism
–– ‘‘HardHard’’ magnetic magnetic
material = material = permanent magnetpermanent magnet
‘‘HardHard’’ ironiron
Ni, Co, some other Ni, Co, some other
elementselements
CeramicsCeramics
–– ElectromagnetsElectromagnets
MagnetsMagnets
Curie TemperatureCurie Temperature–– will convert a permanent will convert a permanent
magnet to a nonmagnet to a non--magnetic material.magnetic material.
EarthEarth’’s magnetic fields magnetic field–– Proposed by William Proposed by William
GilbertGilbert
–– Aurora Borealis and Aurora Borealis and Aurora Aurora AustralisAustralis
–– Origin unknownOrigin unknown Theorize due to EarthTheorize due to Earth’’s s
rotationrotation
EarthEarth’’s Magnetic Fields Magnetic Field
Approximates bar Approximates bar
magnetmagnet
Known to Known to ‘‘shiftshift’’
with timewith time
Magnetic and true Magnetic and true
poles d/n coincidepoles d/n coincide
–– must apply must apply
magnetic correction magnetic correction
for for ‘‘truetrue’’ directiondirection
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IsogonicIsogonic Lines in AviationLines in Aviation
MagnetismMagnetism
Learning GoalsLearning Goals
–– State the law of poles and describe State the law of poles and describe
the magnetic field.the magnetic field.
–– Identify the cause of magnetism, and Identify the cause of magnetism, and
tell why some materials can be tell why some materials can be
magnetized and others cannot.magnetized and others cannot.
–– Analyze some aspects of EarthAnalyze some aspects of Earth’’s s
magnetic field.magnetic field.
Questions: 14Questions: 14--1818
ElectromagnetismElectromagnetism
Interaction of electrical and magnetic Interaction of electrical and magnetic
effects.effects.
––Moving electric fields generate magnetic Moving electric fields generate magnetic
fieldsfields
––Magnetic fields deflect a moving electric Magnetic fields deflect a moving electric
charge.charge.
Telephone receiver.Telephone receiver.
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Telephone ReceiverTelephone Receiver
MicrophoneMicrophone–– Diaphragm that can Diaphragm that can
vibrate and change vibrate and change resistance (carbon resistance (carbon micmic))
Varies electric Varies electric currentcurrent
SpeakerSpeaker–– electromagnetic coilelectromagnetic coil
–– current varies current varies strengthstrength
–– diaphragm vibratesdiaphragm vibrates
Magnetic Force on a Moving Magnetic Force on a Moving
Electric Charge.Electric Charge.
Motors and GeneratorsMotors and Generators
No moving current No moving current -- no forceno force
Moving current Moving current -- force on wireforce on wire
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Motors and GeneratorsMotors and Generators
BrushesBrushes
–– reverse currentreverse current
–– cause attraction to cause attraction to
become repulsion become repulsion
and repulsion to and repulsion to
become and become and
attraction.attraction.
GeneratorsGenerators
Same basic Same basic
principle as motorsprinciple as motors
AC AC -- rotate a wire rotate a wire
loop between loop between
magnetsmagnets
–– FaradayFaraday
How do we How do we
transmit? transmit?
Electrical TransmissionElectrical Transmission
TransformersTransformers
–– Cause change in Cause change in
voltagevoltage
–– windingswindings
–– iron coreiron core
Use to decrease Use to decrease
currentcurrent
–– Decreases IDecreases I22R lossR loss
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TransformersTransformers
For a transformer:For a transformer:
–– VV22 = (N= (N22 / N/ N11) x V) x V11
NN11 = number of windings in primary coil= number of windings in primary coil
NN22 = number of windings in secondary coil= number of windings in secondary coil
VV11 = voltage at primary coil= voltage at primary coil
VV22 = voltage at secondary coil= voltage at secondary coil
Will not work with dcWill not work with dc
ElectronicsElectronics
Emission and control of electronsEmission and control of electrons
TelevisionTelevision
Diodes and TransistorsDiodes and Transistors
Integrated circuitsIntegrated circuits
ElectromagnetismElectromagnetism
Learning GoalsLearning Goals
–– Identify some electromagnetic Identify some electromagnetic
interactions and applications.interactions and applications.
––Distinguish between Distinguish between motorsmotors and and
generatorsgenerators..
–– Explain the principle and use of Explain the principle and use of
transformers.transformers.
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ElectromagnetismElectromagnetism
Questions: 19Questions: 19--2424
Exercises: 25, 27Exercises: 25, 27
Key Terms; Matching, Multiple Key Terms; Matching, Multiple
Choice, and FillChoice, and Fill--inin--thethe--Blank Blank
Questions; Visual Connection and Questions; Visual Connection and
Applying your KnowledgeApplying your Knowledge
General Physical General Physical
ScienceScience
Chapter 8Chapter 8
Electricity and MagnetismElectricity and Magnetism
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