ElectricityElectricityElectric Charge Electric Charge

Static ElectricityConductorsInsulatorsElectroscopeTransferring Charge

Static ElectricityStatic Electricity

Static Electricity the net accumulation of electric

charges on an object

Behavior of Charges opposite charges attract like charges repel

Static ElectricityStatic Electricity

Static Discharge the movement of

electrons to relieve a separation in charge

ConductorsConductors

Conductor material that allows electrons to

move through it easily ex: metals like copper and silver

InsulatorsInsulators

Insulator material that doesn’t allow electrons

to move through it easily ex: plastic, wood, rubber, glass

Transferring ChargeTransferring Charge

Friction Objects will either gain or lose e-

through friction, acquiring a + or – charge

Balloons Socks on carpet Car in winter Dryer

Transferring ChargeTransferring Charge

By Contact (Conduction) Touching objects can transfer charge

by creating a pathway for it to flow from one object to the other

Van De Graaff generator

Transferring ChargeTransferring Charge

Induction Transfer of charge without contact

(objects come close to one another) Wall Doorknob Van de Graaf

ElectricityElectricityElectric CurrentElectric CurrentCircuitPotential DifferenceCurrentResistanceOhm’s Law

CircuitCircuit

Circuit closed path through

which electrons can flow

Potential DifferencePotential Difference

Potential Difference (voltage) difference in electrical potential

between two places (usually the + and – terminals of a battery)

measured in volts (V)

CurrentCurrent

Current flow of electrons through a conductor measured in amperes (A)

ResistanceResistance

Resistance opposition to the flow of electrons measured in ohms ()

Copper - low resistance Tungsten - high resistance

ResistanceResistance

Resistance depends on… the conductor

wire thickness• less resistance

in thicker wires

wire length • less resistance in shorter wires

temp - less resistance at low temps

Concept Check!

If we increase resistance, what will happen to the current (flow of electrons)?

What about if we decrease resistance?

Ohm’s LawOhm’s Law

Ohm’s Law

V = I × RV: potential difference (Volts, V)

I: current (Amps, A)

R: resistance (Ohms, )

• If resistance increases, then the current decreases. • If voltage increases, then the current increases.

Ohm’s LawOhm’s LawA lightbulb with a resistance of 160 is

plugged into a 120-V outlet. What is the current flowing through the bulb?

Electrical PowerElectrical Power

Electrical Power rate at which electrical energy is converted to another form of energy

P = I × VP: power (W)

I: current (A)

V: potential difference (V)

Electrical PowerElectrical Power A calculator has a 0.01-A current flowing through it.

It operates with a potential difference of 9 V. How much power does it use?

ElectricityElectricityElectrical CircuitsElectrical CircuitsCircuit componentsSeries circuitsParallel circuitsHousehold circuits

CircuitCircuit

Circuit closed path through

which electrons can flow

Circuit ComponentsCircuit Components

A - battery C - light bulb

B - switch D - resistor

Series CircuitsSeries Circuits

Series Circuit current travels in a single path

• one break stops the flow of current current is the same throughout circuit

• lights are equal brightness each device receives a fraction of the total

voltage • get dimmer as lights are added

Parallel CircuitsParallel Circuits

Parallel Circuits current travels in multiple paths

• one break doesn’t stop flow current varies in different branches

• takes path of least resistance• “bigger” light would be dimmer

each device receives the total voltage• no change when lights are added

Household CircuitsHousehold Circuits

Combination of parallel circuits too many devices can cause wires to

overheat

Safety Features: fuse - metal melts, breaking circuit circuit breaker - bimetallic strip bends

when hot, breaking circuit

MagnetismMagnetismI. Characteristics of Magnets

Magnetism Magnetic poles Magnetic field Magnetic domain

A. MagnetismMagnetism

force of attraction or repulsion between unlike or like poles

due to the arrangement of electrons

closely related to electricity

B. Magnetic PolesMagnetic Poles

like poles repel

unlike poles attract

a broken magnet creates new poles

C. Magnetic FieldMagnetic Field

area around a magnet where magnetic forces act

field lines show direction of field (NS)

D. Magnetic DomainMagnetic Domain

groups of atoms with aligned magnetic poles

in a magnetized object, domains are all aligned

domain

MagnetismMagnetismII. Uses of Magnetic Fields

Electromagnet Speaker Motor

A. ElectromagnetElectromagnet

strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core

acts like a bar magnet when current is on

B. SpeakerSpeaker

electrical energy mechanical energy

wire coil moves back & forth as its magnetic field interacts with the field of a fixed magnet

forced vibration causes the cone to move sound

C. MotorMotor

electrical energy mechanical energy

electromagnet rotates between the poles of a fixed magnet

commutator reverses the poles of the e’magnet

C. Motor

brushes & wires to battery field magnet

armature & commutatorassembled motor

MagnetismMagnetismIII. Producing Electric Current

Electromagnetic Induction Electric Generator DC & AC Transformer

A. Electromagnetic InductionElectromagnetic Induction

producing a current by moving a wire through a magnetic field

some microphones work just like mini-speakers in reverse

sound waves cause coil to move current

Dynamic Microphone

Coil

B. Electric GeneratorElectric Generator

mechanical energy electrical energy

armature is rotated between magnet poles

magnetic field induces a current in the wire coil

MOTORGENERATOR

B. Electric Generator Hydroelectric Dam

PE of lake water is converted to KE

mechanical KE turns the generator shaft which creates electrical energy

C. DC & ACDirect Current (DC)

current flows in one direction dry cells

Alternating Current (AC) current reverses its direction

at regular intervals electrical outlets

D. TransformerTransformer

increases or decreases AC voltage primary coil AC produces a magnetic field that

induces AC in the secondary coil voltage ratio = ratio of turns in each coil

D. TransformerStep-up Transformer

increases the voltage more turns power plants

Step-down Transformer decreases the voltage fewer turns household appliances

(hairdryers, etc.)