Electricity

Let’s Review…Let’s Review…Atoms have 3 subatomic

particles• Protons = positive• Electrons = negative• Neutrons = neutral

Neutral Atom• “Normal” state• # Protons# Protons = = # Electrons# Electrons

Charged Atom (atom with a positive or negative charge)• Object must gain or lose

electrons• ONLY THE ELECTRONS

MOVE• Measured in Coulombs

Charge & ForceCharge & ForceAttraction

Forces pull together

RepulsionForces push apart

Rules of ChargeLike charges repel (+/+ or -/-)Opposite charges attract (+/-)

+ +

+ -““OppositesOpposites

Attract”Attract”

ElectricityElectricityDefinition: Electricity is the energy associated with

charged particles as they move from place to place

The type of material determines how charges move through them

Conductors• Materials that allow electric charges to move easily• Metals

Insulators• Materials that do NOT allow electrons to flow freely• Rubber, plastic

Forms of ElectricityForms of ElectricityStatic

• Due to build up of charges in or on an object

Current• The flow of electrons in a circuit

Static ElectricityStatic Electricity• Static electricity is electricity “AT REST”• Occurs between 2 objects that become

oppositely charged• Objects involved have unequal electric

charges• Examples

• Clothes sticking together in the dryer (if no dryer sheet is used)

• Hair standing up after being brushed (on days with low humidity)

LightningLightning• Large discharge of static electricity

(electrons transferred from a cloud to the Earth)• Friction from movement of water drops in a

cloud build up positive and negative charges• Bolts can deliver 100 million volts

• Safest place to be in a lightning storm is inside

• Lightning rods are grounded to Earth to distribute the charge

Electric CircuitElectric CircuitAn electric circuit is a path for the

electrons to flow• Flowing Electrons = current

Electricity can only flow through a CLOSED circuit (not an open one)

Hi-LiteHi-LiteThis!This!

Voltage (Potential Difference)Voltage (Potential Difference)• The PUSH that makes electrons flow

(electrons have potential to flow but won’t on their own)

• A difference between energy levels is needed for flow• Electrons flow in a circuit when there is an energy

difference from one end of the energy source to the other end of the energy source (like a battery)

• Units = VOLTS (V)• Symbol = V (capital)• Measured with a Voltmeter

Electric CurrentElectric Current• The FLOW of electric charges in a circuit• Units = Amperes (amps)• Symbol = I• Speed of Current is affected by

• Type, length, & thickness of wire• Voltage• When Voltage , Current

2 Types of Electric Current2 Types of Electric CurrentDirect Current (DC)

• Electron flow is always in the same direction• Ex: Batteries

Alternating Current (AC)• Electrons reverse the direction of flow 60

times per second• Ex: Electricity in the Home

ResistanceResistance• Opposition to the flow of electrons• Unit = Ohm (Ω)• Symbol = R

• Highest resistance in:• Poor conductors • Thin wires• Long wires

Ohm’s LawOhm’s LawRelates Electric Current, Voltage, & Resistance

V = I x R

Voltage

(volts, V)

Current

(amps)

Resistance

(ohms, Ω)

Ohm’s Law ExampleOhm’s Law ExampleCalculate the voltage across a 3Ω resistor if

a 0.5 amp current is flowing through it.

V = I x R

Ohm’s Law ExampleOhm’s Law ExampleCalculate the voltage across a 3Ω resistor if

a 0.5 amp current is flowing through it.

V = I x RV = ?R = 3 ΩI = 0.5 amp

Ohm’s Law ExampleOhm’s Law ExampleCalculate the voltage across a 3Ω resistor if

a 0.5 amp current is flowing through it.

V = I x RV = ?R = 3 ΩI = 0.5 amp

V = (0.5 amp)*(3 Ω )

Ohm’s Law ExampleOhm’s Law ExampleCalculate the voltage across a 3Ω resistor if

a 0.5 amp current is flowing through it.

V = I x R

V = 1.5 v

V = ?R = 3 ΩI = 0.5 amp

V = (0.5 amp)*(3 Ω )

Ohm’s Law Example 2Ohm’s Law Example 2A radio with a resistance of 240 Ω is

plugged into a 120 v outlet. What is the current flowing through the outlet?

V = I x R

Ohm’s Law Example 2Ohm’s Law Example 2A radio with a resistance of 240 Ω is

plugged into a 120 v outlet. What is the current flowing through the outlet?

V = I x RV = 120 vI = ?R = 240 Ω

Ohm’s Law Example 2Ohm’s Law Example 2A radio with a resistance of 240 Ω is

plugged into a 120 v outlet. What is the current flowing through the outlet?

V = I x R120 v = I * 240 Ω V = 120 v

I = ?R = 240 Ω

Ohm’s Law Example 2Ohm’s Law Example 2A radio with a resistance of 240 Ω is

plugged into a 120 v outlet. What is the current flowing through the outlet?

V = I x R

I = 120v / 240 Ω

V = 120 vI = ?R = 240 Ω

120 v = I * 240 Ω

Ohm’s Law Example 2Ohm’s Law Example 2A radio with a resistance of 240 Ω is

plugged into a 120 v outlet. What is the current flowing through the outlet?

V = I x R

I = 0.5 amp V = 120 vI = ?R = 240 Ω I = 120v / 240 Ω

120 v = I * 240 Ω

PowerPower• RATE at which energy is flowing• The measure of the RATE at which

electricity does work or provides energy• Symbol = P• Units = Watts (W)

P = I x V

Power ExamplePower ExampleIf a CD player uses 4.5v with 0.2 amp current, how much power does it use?

P = I x V

Power ExamplePower ExampleIf a CD player uses 4.5v with 0.2 amp current, how much power does it use?

P = I x V

P= ?I = 0.2 ampV= 4.5 v

Power ExamplePower ExampleIf a CD player uses 4.5v with 0.2 amp current, how much power does it use?

P = I x V

P = I * VP= ?I = 0.2 ampV= 4.5 v

Power ExamplePower ExampleIf a CD player uses 4.5v with 0.2 amp current, how much power does it use?

P = I x V

P = (0.2amp)(4.5v)P= ?I = 0.2 ampV= 4.5 v

P = I * V

Power ExamplePower ExampleIf a CD player uses 4.5v with 0.2 amp current, how much power does it use?

P = I x V

P = 0.9 W

P= ?I = 0.2 ampV= 4.5 v

P = (0.2amp)(4.5v)P = I * V

ELECTRICAL EnergyELECTRICAL Energy• Home use of electric energy is based on

the AMOUNT OF ELECTRICAL POWER used per hour

• Measured in kilowatt hours (1000 Watts per hour) = kWh

E = P x t

Electrical Energy ExampleElectrical Energy ExampleYou use your hairdryer for 20 minutes everyday. The hairdryer uses 1000 kW.

How many kilowatt-hours does your hairdryer use in 6 days?

t = 20min/day*6days = 120min = 2hr

E = 1000 kW*2HrE = 2000 kWh

CircuitsCircuits• Closed loop made up of at least two

electrical elements• Consists of at least a power source, wire,

and a device that uses electrical energy (like a light bulb)

Symbols for Circuit DiagramsSymbols for Circuit Diagrams• Wire

• Power Source

• Bulb

• Resistance

• Switch (open) (closed)

Positive Side of Power Source

Negative Side of Power Source

Open CircuitOpen Circuit• Light will not go on because the wire IS

NOT CONNECTED to the battery on both sides; current will NOT flow

Closed CircuitClosed Circuit• Light bulb turns on because the electrical

current CAN now flow through the complete circuit

Series CircuitSeries Circuit• All parts of the circuit are connected one after

another in a loop• There is only one path for the electrons to follow• If one part goes out

• The circuit goes from closed to open• Electricity will not flow• All parts go out

• The voltage is split through each part of the circuit

• The current is the same throughout the circuit• Example: Christmas Tree Lights

Series Circuit ExamplesSeries Circuit Examples

A complete circuit turns the light bulbs on

Series Circuit ExamplesSeries Circuit Examples

The burnt bulb stops the electron flow to the rest of

the circuit

This Light Bulb is Burnt Out

Parallel CircuitParallel Circuit• There is more than one path or branch for

the electrons• If a break occurs in one branch, the

electrons can still flow in the other• The voltage is the same throughout each

branch• The current is split through each branch• Example: Household Wiring

Parallel Circuit ExamplesParallel Circuit Examples

Current divides and has more than one path

A B

PATH #1

PATH #2

Parallel Circuit ExamplesParallel Circuit Examples

Even though Bulb “B” is burnt out, the current still goes

through the other circuit and Bulb “A” remains lit

This Light Bulb is Burnt Out B

A