Chapter 7Chapter 7

ElectricityElectricity

Section 1Section 1ElectricityElectricity

Structure of AtomsStructure of AtomsAtoms contain the following…Atoms contain the following…

ParticleParticle ChargeCharge LocationLocation

ProtonProton +1+1 NucleusNucleus

NeutronNeutron 00 NucleusNucleus

ElectronElectron -1-1 Outside the Outside the nucleusnucleus

Positive and Negative ChargesPositive and Negative Charges

In most atoms, the negative charge cancels In most atoms, the negative charge cancels out the positive charge. These atoms are out the positive charge. These atoms are

said to be said to be electrically neutralelectrically neutral..

Static ElectricityStatic Electricity

The accumulation The accumulation of excess electrical of excess electrical charge on an charge on an object.object.

Ex:Ex: Walking on carpet.Walking on carpet.

Electrons are transferred Electrons are transferred from the carpet to your from the carpet to your shoes.shoes.

LightningLightning is a very large is a very large static chargestatic charge

Charges Exert ForcesCharges Exert Forces

The force on the atoms The force on the atoms depends on…depends on…

1.1. The distance The distance between the atoms.between the atoms.

2.2. The amount of The amount of charge on the charge on the

atoms.atoms.

Opposite charges attract

Like charges repel

• An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled.

• Any charge that is placed in an electric field will be pushed or pulled by the field.

Electric Fields

Earth’s Electric FieldEarth’s Electric Field

Law of Conservation of ChargeLaw of Conservation of Charge

A charge can be transferred from object to A charge can be transferred from object to object, but cannot be created or object, but cannot be created or

destroyed.destroyed.

Static ChargeStatic Charge

Charging Objects By ContactCharging Objects By Contact

Charges can be Charges can be transferred by transferred by rubbing or touching rubbing or touching objects.objects.

Ex:Ex: Rubbing your Rubbing your shoes on carpet shoes on carpet oror rubbing your hair with rubbing your hair with a balloon.a balloon.

Charging By InductionCharging By Induction (Charging at a distance)(Charging at a distance)

Charged objects brought near a neutral object will cause electrons to rearrange

their positions on the neutral object.

Charging at a DistanceCharging at a Distance

The balloon on the The balloon on the left is electrically left is electrically neutral.neutral.

The balloon on the The balloon on the right is right is negativelynegatively charged and charged and produces a produces a positively positively charged areacharged area on the on the sleeve by repelling sleeve by repelling electrons.electrons.

• Lightning is a large static discharge.

Lightning

• A static discharge is a transfer of charge between two objects because of a buildup of static electricity.

• Eventually, enough charge builds up to cause a static discharge between the cloud and the ground.

Lightning

• As the electric charges move through the air, they collide with atoms and molecules. These collisions cause the atoms and molecules in air to emit light.

Thunder

• Lightning also generates powerful sound waves.

• The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat.

• The heat causes air in the bolt's path to expand rapidly, producing sound waves that you hear as thunder.

GroundingGrounding

Connecting an object to Earth.Connecting an object to Earth.

Providing a path for a charge to reach the Providing a path for a charge to reach the Earth Earth prevents an excess charge from prevents an excess charge from building up.building up.

ElectroscopeElectroscope

A device used to A device used to detect an electric detect an electric charge.charge.

Section 2Section 2Electric CurrentElectric Current

Electric CurrentElectric Current

The The netnet movement of electrons in a movement of electrons in a single direction.single direction.

Flows from Flows from higher voltagehigher voltage to to lower voltage.lower voltage.

Measured in Amperes. (amps)Measured in Amperes. (amps)

Voltage DifferenceVoltage Difference

The differences in The differences in electrical chargeselectrical charges..

Measured in Measured in VoltsVolts..

CircuitsCircuits

A closed path that the electric current A closed path that the electric current follows.follows.

A battery can provide the voltage difference A battery can provide the voltage difference needed to keep current flowing.needed to keep current flowing.

ResistanceResistance

Resistance is the tendency for a material Resistance is the tendency for a material to oppose the flow of electrons, changing to oppose the flow of electrons, changing

electrical energy into thermal energy electrical energy into thermal energy

and light.and light.Resistance is measured in ohms Resistance is measured in ohms

Ohm’s LawOhm’s Law

Current (in amps) = Current (in amps) = voltage difference (in volts) voltage difference (in volts)

resistance (in ohms)resistance (in ohms)

I = I = VV

RR

Section 3Section 3Electrical EnergyElectrical Energy

CircuitsCircuits

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

Series and ParallelSeries and Parallel

Series CircuitSeries Circuit

Have only one Have only one loop to flow loop to flow through.through.

EX: flashlights, some EX: flashlights, some holiday lights.holiday lights.

Parallel CircuitsParallel Circuits

Contain Contain two or moretwo or more branches for the current branches for the current to move through.to move through.

The current can flow The current can flow through through bothboth or or eithereither of of the branches.the branches.

Advantage:Advantage: When one When one branch opens the current branch opens the current continues to flow through continues to flow through the other branches.the other branches.

Household CircuitsHousehold Circuits

A combination of A combination of parallel circuits parallel circuits connected in a connected in a network.network.

Protection From OverheatingProtection From Overheating

FusesFuses: Contain a small : Contain a small piece of metal that piece of metal that melts when it melts when it becomes overheated, becomes overheated, breaking the circuit breaking the circuit and stopping flow of and stopping flow of current.current.

Circuit BreakerCircuit Breaker

A circuit breaker contains a piece of metal that bends when the current in it is so large that it gets hot.