electricity
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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
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