Great Ideas in Science: Lecture 4 Electricity and Magnetism
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Transcript of Great Ideas in Science: Lecture 4 Electricity and Magnetism
Great Ideas in Science:Great Ideas in Science:Lecture 4Lecture 4
Electricity and Electricity and MagnetismMagnetism
Professor Robert HazenProfessor Robert Hazen
UNIV 301UNIV 301
Great IdeaGreat Idea: : Electricity and Electricity and magnetism are two different magnetism are two different
aspects of one aspects of one Force — the electromagnetic force.Force — the electromagnetic force.
Electricity and magnetism Electricity and magnetism are two aspects of the are two aspects of the
same force.same force.All All magnetsmagnets have both north and have both north and
south south polespoles
Static electricityStatic electricity is manifest as a is manifest as a force between force between chargedcharged objects objects
Electricity produces magnetic Electricity produces magnetic effectseffects
Moving magnets produce Moving magnets produce electricityelectricity
TonightTonight’’s Outlines Outline
NatureNature’’s Other Forcess Other Forces MagnetismMagnetism Static ElectricityStatic Electricity Batteries and Electric CircuitsBatteries and Electric Circuits Magnetic Effects from Electricity Magnetic Effects from Electricity Electrical Effects from Electrical Effects from
MagnetismMagnetism Electromagnetic RadiationElectromagnetic Radiation
MagnetismMagnetism Magnetic ForceMagnetic Force
Natural magnetic Natural magnetic mineralsminerals
Earth is a giant magnetEarth is a giant magnet Used in navigationUsed in navigation
William GilbertWilliam Gilbert All magnets are dipolesAll magnets are dipoles Like repels, unlike Like repels, unlike
attractsattracts Earth is a dipole Earth is a dipole
magnetmagnet
Magnetic FieldMagnetic Field
Magnetism at Different Magnetism at Different Scales Scales
Northern LightsNorthern Lights
Magnetic BacteriaMagnetic Bacteria
Static ElectricityStatic Electricity NewtonNewton’’s First Laws First Law
GreeksGreeks’’ Observations Observations Electrical chargeElectrical charge
ElectricityElectricity Static electricityStatic electricity Two kinds of chargeTwo kinds of charge Opposites attract Opposites attract Like repelsLike repels
Benjamin Franklin, Benjamin Franklin, ca.1750ca.1750
Benjamin Franklin – single electrical Benjamin Franklin – single electrical fluidfluid Transfer of electronsTransfer of electrons Positive and negative chargesPositive and negative charges
Atomic structureAtomic structure
LightningLightning Lightning occurs when the negatively-Lightning occurs when the negatively-charged clouds interact with the positive charged clouds interact with the positive
charged groundcharged ground
LightningLightning Lightning occurs when the negatively-Lightning occurs when the negatively-charged clouds interact with the positive charged clouds interact with the positive
charged groundcharged ground
The Lightning RodThe Lightning RodElectrons are conducted Electrons are conducted
harmlessly harmlessly
from clouds into the groundfrom clouds into the ground
CoulombCoulomb’’s Law, ca.1785s Law, ca.1785
221
d
qkqF
CoulombCoulomb’’s Law, ca.1785s Law, ca.1785
Charles CoulombCharles Coulomb ExperimentsExperiments
CoulombCoulomb’’s Law:s Law: Force is related to charge and Force is related to charge and
distance distance
1 Coulomb = 6.3 x 101 Coulomb = 6.3 x 101818 electrons electrons
221
d
qkqF
Force of Electricity vs. Force of Electricity vs. GravityGravity
CoulombCoulomb’’s Law:s Law:FFee = k = kee(q(q11 X q X q22)/d)/d22
Gravitational Force:Gravitational Force:FFgg = k = kgg(m(m11 X m X m22)/d)/d22
The Electrical FieldThe Electrical Field
The force felt by The force felt by a charge a charge located at a located at a particular pointparticular point
Differs from the Differs from the magnetic dipole magnetic dipole fieldfield
Frogs and Animal Frogs and Animal ElectricityElectricityca. 1790ca. 1790
Frogs and Animal Frogs and Animal ElectricityElectricityca. 1790ca. 1790
Alessandro VoltaAlessandro Volta’’s s Response (ca.1800)Response (ca.1800)
Alessandro VoltaAlessandro Volta’’s s Response (ca.1800)Response (ca.1800)
The BatteryThe Battery
The BatteryThe Battery
Three Parts of an Electric Three Parts of an Electric CircuitsCircuits
1.1. Source of electrical energySource of electrical energy
2.2. Closed pathClosed path
3.3. Device to use electrical Device to use electrical energyenergy
Electric CircuitsElectric Circuits
Electric CircuitsElectric Circuits
Two Kinds of Two Kinds of Electric CircuitsElectric Circuits
Series circuit vs. parallel circuitSeries circuit vs. parallel circuit
OhmOhm’’s Laws Law Flow of ElectricityFlow of Electricity
Current (amps)Current (amps) 1 amp=1 coulomb/sec1 amp=1 coulomb/sec
Voltage (volts)Voltage (volts) Amount of power in circuitAmount of power in circuit
Electrical Resistance (ohms)Electrical Resistance (ohms)
OhmOhm’’s Laws Law Current is directly proportional to voltage and Current is directly proportional to voltage and
inversely proportional to resistanceinversely proportional to resistance Equation: Equation:
LoadLoad Equation:Equation:
IRV
IVP
Hans Christian Oersted, Hans Christian Oersted, 18201820
The ElectromagnetThe Electromagnet
Magnetic Effects Magnetic Effects from Electricityfrom Electricity
Magnetic Effects Magnetic Effects from Electricityfrom Electricity
The Electric MotorThe Electric MotorNorth and South poles flip during rotary North and South poles flip during rotary
motion.motion.
The Electric MotorThe Electric MotorNorth and South poles flip during rotary North and South poles flip during rotary
motion.motion.
Michael Faraday, 1831Michael Faraday, 1831Electrical Effects from Electrical Effects from
MagnetismMagnetism
Michael Faraday, 1831Michael Faraday, 1831Electrical Effects from Electrical Effects from
MagnetismMagnetism Electromagnetic inductionElectromagnetic induction Electrical fields and currents can be Electrical fields and currents can be
produced by changing magnetic produced by changing magnetic fieldsfields
Electric GeneratorsElectric Generators
Move a coil of wires next to Move a coil of wires next to magnets to create electricitymagnets to create electricity
Car alternatorCar alternator
Turbines (power plants)Turbines (power plants) Wind Wind WaterWater Steam - Coal/Nuclear power Steam - Coal/Nuclear power
plantsplants
James Clark Maxwell, James Clark Maxwell, 18551855
MaxwellMaxwell’’s Laws, 1855s Laws, 1855
Four equations describe the behaviors of Four equations describe the behaviors of
electricity and magnetismelectricity and magnetism
1. Coulomb1. Coulomb’’s Law of static electricity s Law of static electricity
2. All magnets have both north and south 2. All magnets have both north and south
polespoles
3. Electricity produces magnetic effects3. Electricity produces magnetic effects
4. Moving magnets produce electricity4. Moving magnets produce electricity
These equations lead to prediction of waves:These equations lead to prediction of waves:
1. Waves travel 186,000 miles per second1. Waves travel 186,000 miles per second
2. Light is a consequence of electricity 2. Light is a consequence of electricity
and and
magnetism switching back and forthmagnetism switching back and forth
The Electromagnetic The Electromagnetic SpectrumSpectrum
MaxwellMaxwell’’s equations predict more wavess equations predict more waves Hertz discovers radio wavesHertz discovers radio waves