Transcript Model PowerPoint

Defining Electricity and
its Major Components
Mr. Scheu
So what is this mysterious stuff
that we call electricity?
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Electricity surrounds us and for most of us, life without electricity
would be totally different. Electricity can be used in a wide variety
of ways
– For example:
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Electric motors turn electricity into motion. (locomotives)
Light bulbs turn electricity into light
Computers turn electricity into information. (this PowerPoint)
TVs turn electricity into moving pictures. (the Young Frankenstein DVD)
Speakers turn electricity into sound waves. (music on your radio)
Toasters, hair dryers and space heaters turn electricity into heat.
X-ray machines turn electricity into X-rays.
How would life be without electricity?
– we would revert back to fireplaces for heat, wood-fired stoves for
cooking, candles for light and the slide rules for computation, and to
talk over long distances, we are left with smoke signals and postcards.
Objectives
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Today we will:
– Define electrical terms
– Discuss the components of an electrical circuit
– Describe how electrical energy is measured
– Define Ohm’s law and illustrate the
relationship between voltage, amperage,
watts, and ohms of resistance
Electricity Basics
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Electricity—
– a source of energy
that can be converted
to light, heat, or
power.
– A movement of
electrons known as
electrical current
Theories of Current Flow
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Electron Theory of
Current Flow
– Belief that electrons
flow from a negatively
charged atom to a
positively charged
electrons
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Conventional Theory
of Current Flow
– Theory that current
flowed from positively
charged atoms to
negatively charged
atoms
Both Theories are still in use today, and it is
important to not confuse the two.
Electrical Circuits
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source
A simple circuit must contain
Wires
1) A source of electricity to
start the flow of electrons (a
battery, etc.)
2) A conductor that the
electrons flow through
3) a load or consumer to use
the flow of electrons (a light
bulb, motor, etc.)
–
Load—any device that
converts electrical energy
into another form of useable
energy
4) A conductor connected from
the load, back to the source
Complete vs incomplete circuit
load
Generating Electrical Current
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Where is electricity generated?
– Electricity is produced from a generator
(example: power plant)
– Generator—converts energy from other forms,
and causes electrons to flow through the
circuit
 Examples of converted energy include:
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Water
Steam
Wind
Any others?
Other types of generators…
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Storage Batteries (chemical
generators): generate electrical current by
chemical reactions from chemicals stored
inside the batteries
– Wet-cell battery– reaction between the
electrodes and the electrolyte solution
– Dry-cell battery—electrolyte is a compound in
a paste form
Other types of generators…
Mechanical energy: a magnetic force is used
to move electrons; known as electromagnetic
induction
 Piezo electricity: electricity that is produced
when pressure or force is applied
 Thermoelectric process: electricity produced
by heat energy; the more heat, the more current
produced
 Solar power: uses photocells to generate
electrical current
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Journey of Electricity
from being generated to use
Conductors and Insulators
Resistance—tendency of an element or material
to prevent electrical flow
 Conductors—elements and materials that have
low resistance (Gold, Silver, and Copper are
good conductors)
 Insulators—elements that do not readily allow
electrical current to flow through them (glass,
porcelain, cotton, dry wood)
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– Insulating ability may be lost when material becomes
wet
How Electrical Energy is Measured
Electrical current—the flow of electrons
through the conductor; measured in
amperes (A or amps for short)
 Amperage—the rate of electrical current
flow per second
 Similar to flow of water (gallons per
minute) of water pump
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How Electrical Energy is Measured
Voltage (V or volt)– potential force that
causes current to flow in conductor
 Compared to pounds per square inch of
pressure in the water pipe
 Current cannot exist without the pressure
of voltage to force it through the
conductor
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How Electrical Energy is Measured
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Electrons do not flow freely through even the best
conductors, just as water must overcome friction of the
pipe wall to flow through a pipe
Ohm ( Ω )– the unit of measure of the resistance to
electrical flow
– Affected by
 The elements of which the conductors are made
 Length of conductors
– The longer the conductor, the greater the resistance to current flow
 Cross-sectional area of conductors
– The smaller the diameter of the wire, the greater the resistance to flow
 Temperature of conductor
– The hotter the wire, the more resistance to current flow
Relating Voltage, Amperage, and
Ohms of Resistance
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Ohm’s law--the flow of electricity through the conductor is always directly
proportional to the voltage it produces
Amperes= Volts/Ohms
Volts= Amperes x Ohms
Volts
Ohms= Volts/Amperes
Amperage X Ohms
Ohm’s Law in Triangle expression
Example Problems
20 A = 120 V
120 V = 20 A x 6 Ohms
6 Ohms
6 Ohms = 120 V
20 A
Relating Voltage, Amperage, and
Watts
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Watt—a measure of electrical power, or the amount of electrical energy the load or
consumer uses
The higher the wattage the rating, the faster the electrical energy is being converted
Volts= Watts/Amps
Watts= Volts x Amps
Watts
Amps= Watts/Volts
Amperage X Voltage
Wattage formulas in Triangle Expression
Sample Problem:
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Suppose six large 200-watt bulbs are to be
installed in a 120 volt electrical circuit.
How many amps must flow when the
lights burn at rated wattage? The source
of electrical current will supply 120 volts of
pressure. Six bulbs will draw 1,200 watts
of power or energy (6 x 200 = 1,200
watts).
Solution
Which formula must we use?
 A=W/V
 (1200 watts/120 volts) = 10 amps
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Activity
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Complete the worksheet using the given
formulas for calculating amps, volts, ohms
and watts
Review
What is electricity?
What are the 3 components of an electrical
circuit?
 Describe how electrical energy is measured, and
what the different terms, such as amps, volts,
and ohms mean.
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Tomorrow, we will continue our discussion on
electricity as we begin to talk about wiring
outlets and light fixtures and other appliances
within our homes.