Magnetism and Magnetism and ElectromagnetismElectromagnetism

The basics of magnetismThe basics of magnetism

Named for Magnesia, an island in Named for Magnesia, an island in the Aegean Sea >2000 years agothe Aegean Sea >2000 years ago

Lodestones or magnetite, FeLodestones or magnetite, Fe22OO33

Chinese used magnets as Chinese used magnets as compasses in the 12compasses in the 12thth century century

The basics of magnetismThe basics of magnetism

1750 in England, John Mitchell 1750 in England, John Mitchell shows that magnetic poles obey the shows that magnetic poles obey the inverse-square lawinverse-square law1820 Oersted discovered that 1820 Oersted discovered that magnetism is related to electricity… magnetism is related to electricity… Ampere later proposed that electric Ampere later proposed that electric currents are the source of all currents are the source of all magnetismmagnetism

Magnetic Forces and PolesMagnetic Forces and Poles

Like the electrostatic force it can repel or Like the electrostatic force it can repel or attractattract““regions” of magnets called magnetic regions” of magnets called magnetic poles give rise to magnetic forcespoles give rise to magnetic forcesAll magnets have both a north and south All magnets have both a north and south polepoleLike poles repel, opposite poles attractLike poles repel, opposite poles attractNo magnetic monopoles exist in natureNo magnetic monopoles exist in nature

Magnetic FieldsMagnetic Fields

The space around a magnet is The space around a magnet is “altered”… the alteration is called a “altered”… the alteration is called a magnetic fieldmagnetic field

Lines of force… always in closed Lines of force… always in closed loopsloops

Magnetic Field of a Bar Magnet

Earth has a magnetic fieldEarth has a magnetic field

Magnetic materialsMagnetic materials

Magnetic materials (cont’d)Magnetic materials (cont’d)

Magnetic force is due to the motion of Magnetic force is due to the motion of electric charges electric charges Magnetism is produced by two motions of Magnetism is produced by two motions of electrons… their spin and their orbiting electrons… their spin and their orbiting motion about the nucleusmotion about the nucleusThe space around a moving electric charge The space around a moving electric charge is “altered”… the alteration is called a is “altered”… the alteration is called a magnetic fieldmagnetic field

Magnetic materials (cont’d)Magnetic materials (cont’d)

In many substances, magnetism In many substances, magnetism produced cancels outproduced cancels outIn some materials… such cancellation In some materials… such cancellation does not occur… called Ferromagnetic does not occur… called Ferromagnetic materials such as iron, nickel, cobalt, materials such as iron, nickel, cobalt, and alloys e.g. alnico… an alloy of and alloys e.g. alnico… an alloy of aluminum – nickel - cobaltaluminum – nickel - cobalt

ElectromagnetismElectromagnetism

1820, Oersted finds that a current carrying 1820, Oersted finds that a current carrying wire will cause a compass needle to deflectwire will cause a compass needle to deflectImplication: the current carrying wire itself Implication: the current carrying wire itself behaves like a magnet (since it can exert a behaves like a magnet (since it can exert a force on another magnet… like a force on another magnet… like a permanent magnet would)permanent magnet would)Let’s use field theory to understand what’s Let’s use field theory to understand what’s happeninghappening

Magnetic Field for a coil of wire called a Magnetic Field for a coil of wire called a solenoidsolenoid

Magnetic Field for Solenoid with an Magnetic Field for Solenoid with an Iron CoreIron Core

Electromagnetism (cont’d)Electromagnetism (cont’d)

1820, Oersted finds that a current carrying 1820, Oersted finds that a current carrying wire will cause a compass needle to wire will cause a compass needle to deflect… so there was a discovery waiting deflect… so there was a discovery waiting to be made…to be made…

1832, Michael Faraday found that a 1832, Michael Faraday found that a changing magnetic field could produce an changing magnetic field could produce an electric current… electromagnetic electric current… electromagnetic inductioninduction

Principle underlying electric generatorsPrinciple underlying electric generators

Contrasting Electric motors and generatorsContrasting Electric motors and generators

Electric motors – convert electrical Electric motors – convert electrical energy into mechanical energy… the energy into mechanical energy… the motion of electrons into the motion of motion of electrons into the motion of something elsesomething else

Electric generators – convert Electric generators – convert mechanical energy into electrical mechanical energy into electrical energy… the motion of something into energy… the motion of something into the motion of electronsthe motion of electrons

Electricity & MagnetismElectricity & Magnetism

Static, Currents, CircuitsStatic, Currents, Circuits

Magnetic Fields & Electro MagnetsMagnetic Fields & Electro Magnets

Motors & GeneratorsMotors & Generators

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The world is filled with The world is filled with electrical electrical chargescharges::

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What is this electrical What is this electrical potentialpotential called? called?

Static ElectricityStatic Electricity

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Static ElectricityStatic Electricity

The The build upbuild up of an electric charge on of an electric charge on the the surfacesurface of an object. of an object.The charge builds up but The charge builds up but does not does not flow.flow.Static electricity is Static electricity is potential energypotential energy. . It does It does notnot move. It is move. It is storedstored..

Static Discharge…Static Discharge…

Occurs when there is a Occurs when there is a lossloss of static of static electricity due to three possible electricity due to three possible things:things:

FrictionFriction - rubbing - rubbing

ConductionConduction – direct contact – direct contact

InductionInduction – through an electrical – through an electrical field (not direct contact)field (not direct contact)

Electricity that Electricity that movesmoves……

CurrentCurrent: The flow of electrons from : The flow of electrons from one place to another.one place to another.

Measured in Measured in amperesamperes (amps) (amps)

KineticKinetic energy energy

How can we How can we controlcontrol currents? currents?

With With circuitscircuits..

CircuitCircuit: is a : is a pathpath for the flow of for the flow of electrons. We use electrons. We use wireswires..

There are 2 types of currents:There are 2 types of currents:

Direct Current (DC)Direct Current (DC) – Where – Where electrons flow in the electrons flow in the samesame direction direction in a wire. in a wire.

There are 2 types of currents:There are 2 types of currents:

Alternating Current (AC)Alternating Current (AC) – electrons – electrons flow in flow in differentdifferent directions in a wire directions in a wire

There are 2 types of circuits:There are 2 types of circuits:

Series CircuitSeries Circuit: the components are : the components are lined up along lined up along oneone path. If the path. If the circuit is broken, circuit is broken, all all components turn components turn off.off.

Series CircuitSeries Circuit

There are 2 types of circuits:There are 2 types of circuits:

Parallel CircuitParallel Circuit – there are – there are severalseveral branching paths to the components. branching paths to the components. If the circuit is broken at any one If the circuit is broken at any one branch, branch, only the components on that only the components on that branch will turn offbranch will turn off..

Parallel CircuitParallel Circuit

Conductors vs. InsulatorsConductors vs. Insulators

ConductorsConductors – material through which – material through which electric current flows electric current flows easilyeasily..

InsulatorsInsulators – materials through which – materials through which electric current electric current cannot movecannot move..

ExamplesExamples

ConductorsConductors::MetalMetal

WaterWater

InsulatorsInsulators::StyrofoamStyrofoam

RubberRubber

PlasticPlastic

PaperPaper

What is Resistance?What is Resistance?

The The oppositionopposition to the flow of an to the flow of an electric current, producing electric current, producing heatheat..The The greatergreater the resistance, the the resistance, the lessless current gets through.current gets through.GoodGood conductors have conductors have lowlow resistance.resistance.Measured in Measured in ohms.ohms.

What Influences Resistance?What Influences Resistance?

Material of wireMaterial of wire – aluminum and copper – aluminum and copper have low resistancehave low resistanceThicknessThickness – the thicker the wire the – the thicker the wire the lower the resistancelower the resistanceLengthLength – shorter wire has lower – shorter wire has lower resistanceresistanceTemperatureTemperature – lower temperature has – lower temperature has lower resistancelower resistance

What is Voltage?What is Voltage?

The The measure of energymeasure of energy given to the given to the charge flowing in a circuit.charge flowing in a circuit.

The The greatergreater the voltage, the the voltage, the greater greater the force or “pressure”the force or “pressure” that drives that drives the charge through the circuit.the charge through the circuit.

Difference b/t Volts and AmpsDifference b/t Volts and Amps

Example – you could say that…Example – you could say that…AmpsAmps measure measure how muchhow much water comes water comes out of a hose.out of a hose.

VoltsVolts measure measure how hardhow hard the water the water comes out of a hose.comes out of a hose.

Ohm’s LawOhm’s Law

Resistance = Voltage / CurrentResistance = Voltage / Current

Ohms = Volts / AmpsOhms = Volts / Amps

Practice with Ohm’s LawPractice with Ohm’s Law

OhmsOhms VoltsVolts AmpsAmps

44 100100 2525

1515 150150 1010

22 3030 1515

99 4545 55

66 4848 88

What is an electromagnet?What is an electromagnet?

ElectromagnetElectromagnet – a magnet made – a magnet made from a from a current bearing coilcurrent bearing coil of wire of wire wrapped around an wrapped around an iron or steel core.iron or steel core.

What is a generator?What is a generator?

GeneratorGenerator – a machine that changes – a machine that changes mechanicalmechanical energy to energy to electricalelectrical energyenergy

Usually use Usually use movingmoving magnets to magnets to create create currentscurrents in coils of wire. in coils of wire.

What is a motor?What is a motor?

MotorMotor – a device that changes – a device that changes electrical electrical energy to energy to mechanical mechanical energy that can do energy that can do workwork..