Download Electricity Basics

Electricity
Let’s Review…
Atoms have 3 subatomic
particles
Charged Atom (atom with a
positive or negative charge)
• Protons = positive
• Object must gain or lose
• Electrons = negative
electrons
• Neutrons = neutral
• ONLY THE ELECTRONS
Neutral Atom
• “Normal” state
• # Protons = # Electrons
MOVE
• Measured in Coulombs
Charge & Force
Attraction
Forces pull together
“Opposites
Attract”
+ -
Repulsion
Forces push apart
+
Rules of Charge
Like charges repel (+/+ or -/-)
Opposite charges attract (+/-)
+
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
Static
• Due to build up of charges in or on an
object
Current
• The flow of electrons in a circuit
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
• 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
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)
• 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
•
•
•
•
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
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
• Opposition to the flow of electrons
• Unit = Ohm (Ω)
• Symbol = R
• Highest resistance in:
• Poor conductors
• Thin wires
• Long wires
Ohm’s Law
Relates Electric Current, Voltage, & Resistance
V=IxR
Voltage
Current
Resistance
(volts, V)
(amps)
(ohms, Ω)
Ohm’s Law Example
Calculate the voltage across a 3Ω resistor if
a 0.5 amp current is flowing through it.
V=IxR
Ohm’s Law Example
Calculate the voltage across a 3Ω resistor if
a 0.5 amp current is flowing through it.
V=IxR
V=?
R=3Ω
I = 0.5 amp
Ohm’s Law Example
Calculate the voltage across a 3Ω resistor if
a 0.5 amp current is flowing through it.
V=IxR
V=?
R=3Ω
I = 0.5 amp
V = (0.5 amp)*(3 Ω )
Ohm’s Law Example
Calculate the voltage across a 3Ω resistor if
a 0.5 amp current is flowing through it.
V=IxR
V=?
R=3Ω
I = 0.5 amp
V = (0.5 amp)*(3 Ω )
V = 1.5 v
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=IxR
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=IxR
V = 120 v
I=?
R = 240 Ω
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=IxR
V = 120 v
I=?
R = 240 Ω
120 v = I * 240 Ω
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=IxR
V = 120 v
I=?
R = 240 Ω
120 v = I * 240 Ω
I = 120v / 240 Ω
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=IxR
V = 120 v
I=?
R = 240 Ω
120 v = I * 240 Ω
I = 120v / 240 Ω
I = 0.5 amp
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=IxV
Power Example
If a CD player uses 4.5v with 0.2 amp
current, how much power does it use?
P=IxV
Power Example
If a CD player uses 4.5v with 0.2 amp
current, how much power does it use?
P=IxV
P= ?
I = 0.2 amp
V= 4.5 v
Power Example
If a CD player uses 4.5v with 0.2 amp
current, how much power does it use?
P=IxV
P= ?
I = 0.2 amp
V= 4.5 v
P=I*V
Power Example
If a CD player uses 4.5v with 0.2 amp
current, how much power does it use?
P=IxV
P= ?
I = 0.2 amp
V= 4.5 v
P=I*V
P = (0.2amp)(4.5v)
Power Example
If a CD player uses 4.5v with 0.2 amp
current, how much power does it use?
P=IxV
P= ?
I = 0.2 amp
V= 4.5 v
P=I*V
P = (0.2amp)(4.5v)
P = 0.9 W
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=Pxt
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
• 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
Positive Side of
Power Source
• Wire
• Power Source
• Bulb
Negative Side of
Power Source
• Resistance
• Switch (open)
(closed)
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
• Light bulb turns on because the electrical
current CAN now flow through the
complete 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
A complete circuit turns the
light bulbs on
Series Circuit Examples
This Light
Bulb is
Burnt Out
The burnt bulb stops the
electron flow to the rest of
the 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
A
PATH #1
PATH #2
Current divides and has
more than one path
B
Parallel Circuit Examples
A
B
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