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