These notes are for Physics 3 students. They give a background on current, resistance, voltage, and circuits

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Electricity :

Electricity

Let’s Review… :

Let’s Review… Atoms have 3 subatomic particles
Protons = positive
Electrons = negative
Neutrons = neutral
Neutral Atom
“Normal” state
# Protons = # Electrons Charged Atom (atom with a positive or negative charge)
Object must gain or lose electrons
ONLY THE ELECTRONS MOVE
Measured in Coulombs

Charge & Force :

Charge & Force Attraction
Forces pull together
Repulsion
Forces push apart
Rules of Charge
Like charges repel (+/+ or -/-)
Opposite charges attract (+/-) “Opposites
Attract”

Electricity :

Electricity Definition: 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 Electricity :

Forms of Electricity Static
Due to build up of charges in or on an object
Current
The flow of electrons in a circuit

Static Electricity :

Static 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)

Lightning :

Lightning 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 Circuit :

Electric Circuit An 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-Lite
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 Current :

Electric 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 Current :

2 Types of Electric Current Direct 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

Resistance :

Resistance Opposition to the flow of electrons
Unit = Ohm (Ω)
Symbol = R
Highest resistance in:
Poor conductors
Thin wires
Long wires

Ohm’s Law :

Ohm’s Law Relates Electric Current, Voltage, & Resistance
V = I x R Voltage
(volts, V) Current
(amps) Resistance
(ohms, Ω)

Ohm’s Law Example :

Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it.
V = I x R

Ohm’s Law Example :

Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it.
V = I x R V = ?
R = 3 Ω
I = 0.5 amp

Ohm’s Law Example :

Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it.
V = I x R V = ?
R = 3 Ω
I = 0.5 amp V = (0.5 amp)*(3 Ω )

Ohm’s Law Example :

Ohm’s Law Example Calculate 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 Ω
I = 0.5 amp V = (0.5 amp)*(3 Ω )

Ohm’s Law Example 2 :

Ohm’s Law Example 2 A 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 2 :

Ohm’s Law Example 2 A 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 V = 120 v
I = ?
R = 240 Ω

Ohm’s Law Example 2 :

Ohm’s Law Example 2 A 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 120 v = I * 240 Ω V = 120 v
I = ?
R = 240 Ω

Ohm’s Law Example 2 :

Ohm’s Law Example 2 A 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 v
I = ?
R = 240 Ω 120 v = I * 240 Ω

Ohm’s Law Example 2 :

Ohm’s Law Example 2 A 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 v
I = ?
R = 240 Ω I = 120v / 240 Ω 120 v = I * 240 Ω

Power :

Power 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 Example :

Power Example If a CD player uses 4.5v with 0.2 amp current, how much power does it use?
P = I x V

Power Example :

Power Example If 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 amp
V= 4.5 v

Power Example :

Power Example If a CD player uses 4.5v with 0.2 amp current, how much power does it use?
P = I x V P = I * V P= ?
I = 0.2 amp
V= 4.5 v

Power Example :

Power Example If 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 amp
V= 4.5 v P = I * V

Power Example :

Power Example If 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 amp
V= 4.5 v P = (0.2amp)(4.5v) P = I * V

ELECTRICAL Energy :

ELECTRICAL 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 Example :

Electrical Energy Example You 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*2Hr
E = 2000 kWh

Circuits :

Circuits 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 Diagrams :

Symbols for Circuit Diagrams Wire
Power Source
Bulb
Resistance
Switch (open) (closed) Positive Side of Power Source Negative Side of Power Source

Open Circuit :

Open Circuit Light will not go on because the wire IS NOT CONNECTED to the battery on both sides; current will NOT flow

Closed Circuit :

Closed Circuit Light bulb turns on because the electrical current CAN now flow through the complete circuit

Series Circuit :

Series 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 Examples :

Series Circuit Examples A complete circuit turns the light bulbs on

Series Circuit Examples :

Series Circuit Examples The burnt bulb stops the electron flow to the rest of the circuit This Light Bulb is Burnt Out

Parallel Circuit :

Parallel 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 Examples :

Parallel Circuit Examples Current divides and has more than one path A B PATH #1 PATH #2

Parallel Circuit Examples :

Parallel 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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