Download U3e Test Review Electrical Technology 1

TEST REVIEW ELECTRONS
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Electricity begins with Electrons.
ATOMS
Electron cloud surrounds an
atom’s nucleus
Nucleus is made of
Protons and Neutrons
Electrons – negative charge
Protons – positive charge
Neutrons – zero charge (neutral)
U3e-L1
REVIEW CIRCUITS
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The paths that electrons travel are called circuits.
Circuits must consist of three things:
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Power Source – with positive
and negative terminals.
ELECTRONS
move
• Conductor – the path the
from
negative
(
)
electrons travel along.
• Load terminal
– this is what to
the
electricity
powers ((e.g.
positive
+ )motor,
light bulb)
terminal
LOAD
U3e-L1
REVIEW CONDUCTORS
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Conduct – from Latin for “leading, guiding.”
A conductor is any material that allows electrons
to easily flow.
Remember the atom:
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–
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Conductors’ electrons are not tightly bound to the atom.
Conductors have free electrons.
Which material has free electrons, Wood or
Metal?
Metals conduct electricity easily.
U3e-L1
Review INSULATORS
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Insulate – from Latin for “separate, divided.”
An insulator is any material that impedes the
flow of electrons.
Remember the atom:
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Insulators’ electrons are tightly bound to the atom.
Because the electrons don’t move, insulators cannot
conduct electricity very well, if at all.
Which material has bound electrons, Wood or
Metal?
Wood does not have free electrons.
U3e-L1
Bound
Free-electrons
Aluminum
Copper
Plastic
Cotton
Wood
Silver
Gold
Air
Electrons
INSULATOR
CONDUCTOR
Cotton
Wood
Plastic
Air
Copper
Gold
Silver
Aluminum
BOUND ELECTRONS
FREE ELECTRONS
U3e-L1
Review Joule’s Law
• James Joule (1818 – 1889) – showed that heat
and electrical energy are interchangeable.
• Joule’s Law:
Power = Voltage x Current
P=VI
Watts = Volts x Amperes
U3e-L1
Review Ohm’s Law
• George Ohm (1789 – 1854) – a high school and
university mathematics instructor
• Discovered ~1827
• Voltage = Current x Resistance
V=IR
What are the units of this formula?
Volts = Amperes x Ohms
U3e-L1
TERMINOLOGY
• Current (I) – the motion of electrons from one atom
to the next in a material.
– In our circuit, electrons flow from ___________
NEGATIVE terminal
to the ___________terminal.
POSITIVE
– This motion of electrons through our conductor (wire) is
considered current (like water through a pipe).
• Materials that resist current are
called INSULATORS
___________.
• Materials that provide
LOAD
a path for current are called
___________.
CONDUCTORS
• Current is measured in AMPERES (Amps)
U3e-L2
Review TERMINOLOGY
• Voltage (V) – the electric potential between two
points of opposite charge.
• Voltage is the potential energy of the electrical
power source.
• Voltage is measured in Volts (V).
U3e-L2
Review Electric Schematics
1. What is a schematic?
A schematic is a diagram that
represents the elements of a system
without using realistic pictures
2. Which of the following is a schematic?
U3e-L3
Review March 04, 2010
DRILL
1.
What does the following schematic symbol represent?
DC Power Supply
2.
What does the following schematic symbol represent?
AC Power Supply
3.
4.
How many volts are typical in a residential electrical
outlet? 120 volts
What do graphs of DC and AC power sources look
like? Why?
U3e-L8
Review Problems – Joule’s Law
1) Write the given information:
V = 144 Volts
P = 20,000 Watts
I=?
2) Sketch a schematic diagram of the circuit:
Start with power source
Add conductors
P = 20,000 W
Add load
Add current
I=?
+
V = 144V
U3e-L2
Review Problems – Joule’s Law
1) Write the given
information:
V = 144 Volts
P = 20,000 Watts
I=?
2) Sketch a schematic
diagram of the
circuit:
+
R=?
-
V = 5V
I = .7A
3) Rearrange, Substitute, and Solve
P=VxI
I=P/V
I = 20,000W / 144V
R = 138.9 A
U3e-L2
Review Resistance Calculations
• Resistors in series are added:
R1
R2
R3
Total Resistance:
R T = R1 + R2 + R3
U3e-L3
Review Resistance Calculations
• Resistors in parallel: add their reciprocals
R1
R2
R3
Total Resistance:
1
1 1
1
=
R T R1 + R2 + R3
U3e-L3
Review ELECTRIC MOTORS
What is a schematic?
A schematic is a diagram that represents the
elements of a system without using realistic pictures.
How would a schematic which includes an electric
motor look?
Switch = Commutator
Motor
V = 9V
U3e-L8
I
Review ELECTRIC MOTORS
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Now that you know what switches look like in
electrical schematics, draw an electrical schematic
for a lamp plugged into a wall outlet.
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Remember that AC power supplies look like
in electrical schematics.
U3e-L8
Review ELECTRIC MOTORS
Lamp
120 V
U3e-L8
Review TERMINOLOGY
• Resistance (R) –a measure of the degree to which
an object opposes an electric current through it .
• Resisting an electric current often generates heat.
– This is the principle behind how light bulbs work.
• Resistance is measured in Ohms (W – the Greek
letter Omega)
U3e-L2
Review Electric Motors
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Michael Faraday (1791-1867)
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London, England.
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Physicist and Chemist
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First person to successfully
create an electric motor.
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Discovered that electric currents
create a magnetic field, and vice
versa.
U3e-L8
Review ELECTRIC MOTORS
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Electric motors are used everyday in many ways.
A motor’s purpose is to turn electrical energy into
mechanical energy.
Motors work on simple principles of magnetism:
• Opposite poles _____________
ATTRACT
• Like poles _____________
REPEL
N
S
S
S
N
N
U3e-L8
Review Direct Current
• If voltage is constantly 1.5 V, what does its
graph over time look like?
2
1
Voltage (volts)
3
1.5 V
0
2
4
6 8 10 12 14
Time (seconds)
U3e-L8
Review Alternating Current
0
120
+/-120 V
-120
Voltage (volts)
• If voltage is alternating 120 V to -120 V, what
does its graph over time look like?
0
2
4 6 8 10 12 14
Time (seconds)
U3e-L8
Review Electrical Technology
• Electricity can be used in a thousand different ways.
For example:
– Electric motors turn electricity into motion.
– Light bulbs, fluorescent lamps and LEDs turn
electricity into light.
– Computers turn electricity into information.
– Telephones turn electricity into communication.
– TVs turn electricity into moving pictures.
– Speakers turn electricity into sound waves.
– Stun guns turn electricity into pain.
– Toasters, hair dryers and space heaters turn
electricity into heat.
– Radios turn electricity into electromagnetic waves that
can travel millions of miles.
– X-ray machines turn electricity into X-rays.
U3e-L1
Review March 2, 2010
DRILL
ELECTRICAL
1. An electric motor converts _________
energy into __________
MECHANICAL energy.
2. List 4 household objects that use electric
motors.
Fans
ALMOST
Refrigerators
Pumps
Garbage disposer
EVERY
MECHANICAL
Printers
Microwave trays
MOVEMENT
IN
YOUR
HOUSE
Washing machines
DVD players
Vacuums
VCRs
U3e-L6
U3e-L6
U3e-L6
Review Problems – Joule’s Law
Complete problem #5 on your worksheet
U3e-L2
Review Problems – Joule’s Law
5. A Lexus RX 100h hybrid has a 144 Volt battery
system in its trunk. The electric motor that the
batteries power can generate 20,000 Watts of
power. Sketch a schematic diagram of this circuit.
What is the current traveling through this high
voltage circuit?
1) Write the given information:
144
volts
A schematicVis= a
diagram
that
P = 20,000 watts
represents the
elements of a system
I=?
without using realistic pictures
U3e-L2
ReviewProblems – Joule’s Law
1) Write the given information:
V = 144 Volts
P = 20,000 Watts
I=?
2) Sketch a schematic diagram of the circuit:
Start with power source
Add conductors
P = 20,000 W
Add load
Add current
I=?
+
V = 144V
U3e-L2
Review Problems – Joule’s Law
1) Write the given
information:
V = 144 Volts
P = 20,000 Watts
I=?
2) Sketch a schematic
diagram of the
circuit:
+
R=?
-
V = 5V
I = .7A
3) Rearrange, Substitute, and Solve
P=VxI
I=P/V
I = 20,000W / 144V
R = 138.9 A
U3e-L2
• STUDY FOR TEST TOMORROW
• HAND IN REVIEW BEFORE TEST
U3e-L2