Electricity & Magnetism Static, Currents, & Electro Magnets Motors & Generators.

Electricity & MagnetismElectricity & Magnetism

Static, Currents, & Electro MagnetsStatic, Currents, & Electro Magnets

Motors & GeneratorsMotors & Generators

Atoms…Atoms…

Have Have neutronsneutrons, , protonsprotons, and , and electronselectrons..

Protons are Protons are positivelypositively charged chargedElectrons are Electrons are negativelynegatively charged charged

Electrons…Electrons…

Are located on the Are located on the outerouter edges of edges of atoms…they can be atoms…they can be movedmoved..

A A concentrationconcentration of electrons in an of electrons in an atom creates a net atom creates a net negativenegative charge.charge.

If electrons are If electrons are strippedstripped away, the away, the atom becomes atom becomes positivelypositively charged. charged.

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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 of an electric charge on the on the surfacesurface of an object. of an object.

The charge builds up but The charge builds up but does does not flow.not flow.

Static electricity is Static electricity is potential potential energyenergy. 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 of static electricity due to three static electricity due to three possible things:possible things:

FrictionFriction - rubbing - rubbingConductionConduction – direct contact – direct contactInductionInduction – through an electrical – through an electrical field (not direct contact)field (not direct contact)

LightningLightning

Large Large static discharge static discharge between the earth between the earth and clouds.and clouds.

Lightning was found to be Lightning was found to be static electricity static electricity by Ben Franklin.by Ben Franklin.

GroundingGrounding

Conductive path to Earth.Conductive path to Earth.

Lightning rods & plumbing.Lightning rods & plumbing.

The electroscope can be used The electroscope can be used to detect electric chargeto detect electric charge

Electricity that Electricity that movesmoves……CurrentCurrent: The flow of electrons : The flow of electrons

from one place to another.from one place to another.Measured in Measured in amperesamperes (amps) (amps)KineticKinetic energy energyThe amount of electric charge is measured The amount of electric charge is measured

in in coulombscoulombs..1 coulomb is the charge carried by 6.24 x 1 coulomb is the charge carried by 6.24 x

10^18 e¯.10^18 e¯.1 amp (A) is 1 coulomb per sec (C/s)1 amp (A) is 1 coulomb per sec (C/s)

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 in a wire. direction in a wire.

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

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

Conductors vs. InsulatorsConductors vs. Insulators

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

InsulatorsInsulators – materials through – materials through which electric current which electric current cannot cannot movemove..

ExamplesExamples

ConductorsConductors::MetalMetalWaterWater

InsulatorsInsulators::StyrofoamStyrofoamRubberRubberPlasticPlasticPaperPaper

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 – aluminum and copper have low resistancecopper have low resistance

ThicknessThickness – the thicker the wire the – the thicker the wire the lower the resistancelower the resistance

LengthLength – shorter wire has lower – shorter wire has lower resistanceresistance

TemperatureTemperature – lower temperature has – lower temperature has lower resistancelower resistance

Electric CurrentElectric Current

The reason The reason electric charge electric charge flows from one flows from one place to another is voltage.place to another is voltage.

VoltageVoltage is the difference in electrical potential is the difference in electrical potential between two places where e¯ are flowing.between two places where e¯ are flowing.

Voltage is the “Voltage is the “pushpush” that makes electric ” that makes electric charges move.charges move.

Measured in Measured in volts (V).volts (V).

HIGH LOW

BatteriesBatteriesBatteriesBatteries are e¯ pumps. are e¯ pumps.

They provide a voltage difference to a circuit.They provide a voltage difference to a circuit.Types: Types: wet-cellswet-cells & & dry-cellsdry-cells

Kirchoff’s LawsKirchoff’s Laws Kirchoff’s First Law Kirchoff’s First Law states that current states that current

entering a junction is equal to the entering a junction is equal to the current leaving the junction. current leaving the junction.

Kirchoff’s Second Law Kirchoff’s Second Law states that the states that the sum of the voltage drops around a sum of the voltage drops around a complete circuit loop or path is equal to complete circuit loop or path is equal to the applied voltage to the circuit.the applied voltage to 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 water

comes out of a hose.comes 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

Where: Current = IWhere: Current = I Voltage = VVoltage = V Resistance = RResistance = R

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 iron or steel core.core.

What is a generator?What is a generator?

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

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..

That’s It !!!!That’s It !!!!