Download Elec spring 2013

ELECTRICAL SYSTEMS
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ELECTRICITY STANDARDS
5.1 Measure and calculate voltage, current, resistance, and power
consumption in series and parallel circuits, using the appropriate
instrument.
5.2 Components of a circuit, including sources, conductors, circuit
breakers, fuses, controllers, and loads. Examples of some controllers are
switches, relays, diodes, and variable resistors.
5.3 Relationships among voltage, current, and resistance in a simple circuit,
using Ohm’s law.
5.4 Resistance is affected by external factors. (e.g., temperature of
conductor, length of conductor, cross-sectional area of conductor and
material of the conductor).
5.5 Compare and contrast alternating current (AC) and direct current (DC),
and give examples of each.
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Four Parts to an Electrical Circuit
Power Source
Conductor
Load
Control
Provide the force (EMF) to cause electrons
to move. A battery, Generator,
Photovoltaic Cells, Thermocouples
Provides a path for the electrons to flow
through the circuit. Copper is formed into
wires, bars or channels.
The part of the circuit that changes the
energy of moving electrons into some
other useful form of energy. Lights,
Motors, Heating elements are examples.
Regulates the flow of electrons in a circuit.
Switches, potentiometers, thermostats,
transistors are just some examples.
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Schematic Diagrams
A standard way to represent electrical components using graphic symbols.
Battery
AC Generator
Open Switch
Closed Switch
(Off Position)
(On Position)
Ground
i.e. Earth
Resistor
Lamp
(incandescent)
Potentiometer
Draw a schematic for a flashlight.
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Schematic Diagrams
A standard way to represent electrical components using graphic symbols.
Capacitor
Diode
LED
Light Emitting Diode
Transformer
Solenoid
Relay Switch
GFCI
Outlet - GFCI
Ground Fault Circuit Interrupter
Use on Doorbell
Fuse
Circuit
Breaker
In a blue print of a house a
GFCI is represented with a
schematic like the one on
the left
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Parts of the Atom
 An atom has three parts.
Proton
Is positively charged and located in the
nucleus
Neutron
Has no charge and is located in the nucleus
Electron
Is negatively charged and is located in the
electron cloud and orbits the nucleus.
There are the same number
of protons (positive charge)
as electrons (negative charge)
in a balanced atom.
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Creating Free Electrons and
Positive Ions
 When two electrons with like charges get close they
repel one another.
The atom that
is missing an
electron is now
a Positive Ion
A Free Electron is formed and
will randomly drift in the material.
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Insulators and Conductors
 Conductors are noted for having many free electrons.
Metals such as copper, aluminum, gold have many free
electrons and are used in many electrical applications.
Insulators will have few free electrons as
the atoms in these materials have a strong
attraction between the electrons and
protons
Materials such as rubber, glass, ceramics, and most plastics.
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Measuring Devices
 Voltmeter- Measures volts or electrical pressure
 Ohm Meter- measures resistance to electron flow
 Ammeter – measures current or the speed at which
electrons flow.
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Series Circuits
 Provide only one path for electrons to flow.
Electrons flow from
negative to positive. The
negative charged electrons
are repelled from the
negative terminal and
attracted to the positive
terminal.
If one light bulb
goes out…….
they all go out
because the path
is open.
When a circuit is closed the electrons pass
through the conductor to each of the loads and
back to the power source.
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Parallel Circuits
 A circuit in which the loads are connect on different
branches.
Me Too!
Me Too!
I’m a branch
Me Too!
Branches
distribute the
electricity down
different paths.
If one light bulb goes out …...
there is still a path for the electrons to flow through the circuit
so none of the others will go out.
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Combinations of series and parallel
circuits
 When a circuit is wired in series/parallel only parts
of a circuit may be effected when a light fails.
L1
L3
L5
L2
L4
If lamp L3 burns out,
which lamps will remain
on and which will go out?
Only lamp L2 and L3 will be
out the rest will remain on.
If lamp L1 burns out,
which lamps will remain
on and which will go out?
If lamp L1 burns out all the other
lamps, L2, L3, L4, and L5 will also
go out because the path of the
electrons has been open.
Houses are wire in a series/parallel with
several branches with multiple outlets,
lights ceiling fans on each branch.
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Combinations of series and parallel
circuits
Most circuits in a house are series/parallel. Each branch is is
in series with the circuit breaker. Each light or outlet is in
parallel with other items on the branch. Even if one device
stops working, the others will still work.
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Ohm’s Law
 V= Voltage
 I= Amperage
 R= Resistance
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Ohms Law Putting the 3 together
Ohm’s Law is a basic law about electricity.
It shows the mathematical relationship between Electromotive
Force or Voltage (E or V) Current (I) and Resistance (R)
This simple memory device may
be used. Place your finger
over the unknown quantity
and the math equation will
be be displayed
A battery supplies 6 volts
and the resistance is 12
ohms. What is the current?
Current = Voltage/Resistance
Voltage = Current x Resistance
Resistance = Voltage/Current
V
IxR
A current is 3 amps and a
resistance is 40  What is
the voltage?
Voltage = Current x Resistance
Current=Volts/Resistance
6volts/12 =.5amps
3amps x 40 = 120Volts
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V
Ohm’s Law Practice
IxR
1. A circuit has an applied voltage of 100 volts and a resistance
of 1000. What is the current flowing in the circuit?
I=V/R
V = 100 v
I=.1 Amps
I = 100V/1000Ω
I=?
R = 1000Ω
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V
Ohm’s Law Practice
IxR
2. A circuit has an applied voltage of 3 volts and a current flow
of .5amps. What is the resistance required?
V=3v
I = 0.5 amps
R=V/I
R=3v/0.5amps
R= 6 Ω
R=?
3. A circuit has an a current flow of 15amps with an appliance
that has 8  of resistance. What is the applied voltage?
V=?
I = 15 amps
V= I x R
V = 15 amps x 8 Ω
V=120 volts
R=8Ω
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DC  Direct Current
 Current that is produced in a circuit by a steady voltage source.
Electrons flow
from – to +
In direct current the
voltage will go to
maximum or PEAK
(almost) instantly so
on a graph it looks
like this. 
Volts
Direct current is when electrons flow in one direction in a circuit
only.
 http://www.walter-fendt.de/ph14e/electricmotor.htm
0
Time
1 sec
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AC  Alternating Current
 Current that is produced by a voltage source that
changes polarity, or alternates, with time.
In alternating current the voltage goes to PEAK positively then
reverses to zero, the current then goes to PEAK in the negative.
Volts
When the electrons have gone once in each direction makes
cycle and is represented with a sine wave as seen in the graph.
0
Time
http://www.walter-fendt.de/ph14e/generator_e.htm
Draw this graph
on your paper
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Electrical Power
 The rate at which electrical energy is delivered is POWER.
Power is also the rate at which an electrical circuit does the
work to convert the energy of moving electrons into some
other form of energy.
 The unit of measure for Power is the watt.
The letter symbol for Power is P.
The watt is based on on the unit of work, joules per second.
100 watts light bulb uses 100 watts in one hour or 100 watt-hours.
If the 100 watts light bulb uses 100 watts in one hour after ten
hours the bulb has used 1000 watt-hours or 1 Kilowatt-hour.
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The Power Formula
Or V
The formula is P = E x I
 We can calculate the power used by an appliance or
item. Power is equal to the Electromotive Force
(voltage) multiplied by the current.
Using the same technique as the
Ohm’s Law Memory device. To
solve the problems at the Right.
P
An appliance is rated for 120 volts
and draws 10 amps. What is the
power used in one hour?
Formula: P = E x I
Math: P = 120 volts x 10 amps
Answer: P = 1200 watts
ExI
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Questions
15. What is the power used of a circuit that has 120
volts and a current of 12 amps?
A.
B.
C.
D.
12 watts
12 volts
1440 watts
0.1 volts
V = 30 v
I = 12 amps
P=IE P= 12 amps x 120 volts P= 1440 watts
R=?
P= ?
The correct answers is _____
C.
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Questions
16. If a speaker is rated for 8 Ω and it has 0.25 amps
of current flowing to it then what is the
Electromotive force at the speaker?
A.
B.
C.
D.
.5 watts
1 watts
2 watts
16 watts
V=?
I = 0.25 amps
V = IR V=0.25amps x 8 Ω V= 2 volts
R=8Ω
P= ?
P= IE
P= 0.25 amps x 2 volts P= 0.5 watts
A.
The correct answers is _____
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Electrical Safety
Fuses have an internal wire that burns out if a
current is too great.
House Fuse
Car fuses
In-line fuse Holder
and fuse
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Electrical Safety
Circuit breakers
which will shut
off the circuit if
the current flows
to much.
Electrical Panel
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A relay Switch
One circuit is used to
control a second circuit.
When Magnet coil is
turned on it will attract the
steel plate and move the
switch closer turning on
that circuit.
Transformer
The primary coil in a Transformer
produces a magnetic field that
will influence the electrons in the
second coil and current will flow.
Used to step-up or step down
voltage.
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 End of show for 2011
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Potential Difference or Voltage
 Potential difference is electrical potential or the difference
in voltage between two points.
1000 gallons
Just as in this example
there is the potential to
move 1000 Gallons of
water from the upper tank
to the lower tank.
A battery is rated by the number of volts it has or the potential difference
it has between the positive and negative terminals at full charge.
 Potential Difference is measured in Volts
Potential Difference letter symbol is either V or sometimes E
Anytime there is a difference in voltage between two objects
(terminals) there is Potential Difference.
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MasterCard
The Law of Charges
Visa
American Express
Discover
 Like charges
+
Repel
Repel
+
Unlike charges
Attract Attract
+
It should be noted that an area of influence (an electrical field)
exists around each charge. Objects do not have to touch to repel
or attract.
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Electromotive Force
 Electromotive force is the amount of push or force
that is in the wires pushing the electrons.
Electromotive force would
be equal to the pounds per
square inch (PSI) that is the
force of the water going
through the pipe.
60 pounds per
square inch
 Electromotive Force or EMF unit of measure is the Volts
Electromotive force Letter symbol is either V or sometimes E
Electromotive force only exists when electricity is flowing.
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Electrical
Current
 Current is the number
of electrons to pass at one point
in one second. It is the flow of electrons.
Current would be like the
number of gallons per
minute are passing a point
in the pipe.
Gallons per
Minute
Current unit of measure is the Amperes or Amps.
 Currents Letter symbol is an I
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Resistance
 Resistance is opposition to current flow.
Resistance is the friction from the
valve and the sides of the pipe.
The valve and pipe walls
restricts the flow of water
The length of the conductor
(wire) will have an effect on the
current. The shortest extension
cord should be used when using
machines.
Resistance unit of measure is the Ohm or the
omega symbol .
 The letter symbol is an R
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Series Circuits
Only One Path
Here there are two
light bulbs in series.
Power Source
What is missing?
Control – Control
is by disconnecting
a terminal
anywhere in the
circuit or remove a
lamp.
Load
Conductor
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Parallel Circuits
A parallel circuit has
more than one path
each charge can
follow.
Disconnecting a
lamp terminal or
removing a lamp
would only stop one
of the two lamps.
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Electrical Safety
Correct wiring is not enough to prevent
electrical accidents.
Most household circuits usually have an
average voltage of 120 volts. Each device that
is turned on increases the current. If the
current exceeds the circuit’s safety limit, the
wire may overheat.
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Questions
17. If one light on a string of holiday lights burns out
and the rest do not the string is wired?
A.
B.
C.
D.
In series
In parallel
With a fuse.
In combination.
B.
The correct answer is _____
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Questions
18. Current that flows in one direction?
A.
B.
C.
D.
Is AC and supplied by a battery
Is AC and is supplied by a generator
Is DC and is supplied by a generator
Is DC and supplied by a battery.
D.
The correct answer is _____
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Questions
19. A house is typically wired in?
A.
B.
C.
D.
Series
Parallel
Series/Parallel
The dark
C.
The correct answer is _____
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Questions
20. AC current that has 60 hertz is typical in USA.
This means that?
A.
B.
C.
D.
The voltage is at a peak usable 60 volts.
The cycles per second are at 60 times a second
The watts will never exceed 60 watts
The amperes going into a residential home is 60 amps
B.
The correct answer is _____
End of slide show
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Current
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Electrical Current and Magnetic
fields
Electromagnetic fields around a live wire
Compass influenced by current
Electromagnets and Solenoids
How electromagnets work
How speakers work
Electromagnetic induction
How generators work
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