Download Basic Electricity

Basic Electricity
Lesson 2
03/11/2007
by FJM
Everything in the world, whether solid,
liquid, or gas, is made up of atoms.
• Each atom contains some number of
electrons, protons, neutrons, and
other sub-atomic stuff.
• The nucleus (central region) of each
atom contains the protons (positive
charge) and neutrons (no charge).
Electrons (negative charge) live in a
cloud around the outside.
• Since electrons and protons are
charged particles, each atom prefers
to have the same number of electrons
as protons.
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• Atoms of one or more types are
organized into molecules.
• There are only a hundred or so types
of atoms,
• There are an almost infinite number
of different molecules.
• Molecules are the building blocks
from which all real objects are made..
• Molecules are not always so simple.
• Some organic molecules can
comprise hundreds of atoms
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• For historical reasons, we divide the
science and engineering of electrons
into two parts; electricity, and
electronics.
– Electricity is the domain of motors,
light bulbs, generators, and other "large
scale" items.
– Electronics has come to mean the
domain of vacuum tubes, transistors,
integrated circuits, and other "small
scale" items.
• .
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• We have come to realize that orbits
are not a very meaningful concept for
electrons.
• We now describe electrons as existing
in a "cloud" that surrounds the atomic
nucleus.
• At any given instant, an electron has
some statistical likelihood of being
somewhere in that cloud..
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• Some materials are willing to let a few
electrons move from molecule to molecule.
• Materials that let electrons move through
them are called "conductors".
• Although some are better than others, most
metals are good conductors of electricity.
Silver, Gold, and Platinum are very good
conductors but are expensive, so they are
not often used.
• Copper and Aluminum are reasonably good
conductors and are fairly inexpensive.
• Thus the wiring in our houses is copper,
and the high voltage electric lines that we
see crossing the country use aluminum
cables..
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• Materials that do not let electrons move
through them are called "insulators”.
• Glass is an example of a type of material
that keeps its electrons tightly controlled.
• Glass is made of silicon molecules,
organized very tightly in to crystalline
structures.
– Glass is an extremely good insulator.
• Many plastics are good insulators too.
– Plastics are cheap, flexible, and durable.
– That is why the wiring in our houses is covered
with a layer of plastic.
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A single cell from a flashlight creates an electrical force of
1.5 Volts.
A transistor radio battery creates an electrical force of 9
Volts. (There are six little cells of 1.5 Volts each inside of the
9 Volt battery.)
Household electrical outlets are 110 or 120 Volts,
What should you know about voltage?
– Electrons don't move from atom to atom without a reason.
– When electrons are flowing, there is an electrical force
somewhere, pushing them along.
– You might see references to Electromotive Force, or "EMF".
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Current
• Current is the flow rate of electrons through
the circuit.
. The water in your pipes is under pressure
• This pressure is similar to Voltage.
• Voltage is the pressure pushing on the
electrons in a circuit.
• If all of the faucets in your house are
closed, no water flows through the pipes.
• If you open one faucet, some water flows. If
you open all of the faucets, a lot of water
flows.
• This flow of water is similar to electrical
Current.
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Voltage causes Current.
• Voltage and current are not the same
thing, although they are closely
related.
• In simple terms, Voltage causes
Current.
• Given a Voltage and a path for the
electrons, current will flow.
• Given the path, but no Voltage, or
Voltage without the path, there will be
no current.
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Alessandro Volta
• In 1791, Volta was experimenting with
metals and acids and was able to assemble
a pile of cells to form a battery
• He touched a silver spoon and a piece of tin
to his tongue (saliva is slightly acidic) and
connected them with a piece of copper wire.
• He experienced a "sour" taste, and realized
he was experiencing an electrical
phenomenon.
• Each cell was a disk of zinc and a disk of
silver, separated by a layer of brine-soaked
pasteboard.
• We now refer to that original battery as a
Voltaic Pile.
• In Volta's honor, we refer to electrical
pressure as "Voltage" and
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What Causes Voltage?
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Electrons have a negative charge, and Protons have a positive
charge.
– Like-charged particles repel.
– Opposite-charged particles attract.
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Each charged particle that is out of balance exerts some
electrical pressure as it tries to get back into balance.
Electrons push, as they try to get away from each other.
Protons pull, as they try to attract electrons towards them.
The total amount of pressure between two points is measured
as Voltage.
Given a path, electrons will flow away from a negative charge
and towards a positive charge
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The Resistor
• The resistor is a device that is common to
practically every circuit known to man.
• Resistors are designed to have specific values of
resistance. Resistance opposes the flow of
electrons.
• A resistor is a device that limits the amount of
current flowing through a circuit for a particular
applied voltage.
– If the resistance stays the same and the voltage goes down, then
the current decreases.
– If the voltage stays the same, and the resistance goes up, then
the current decreases.
– If the voltage stays the same, and the resistance goes down, then
the current will increase.
• The basic unit of resistance is the ohm.
– 1 Ohm of resistance is defined as ... the resistance of a circuit in
which a 1-amp current flows when 1 volt is applied.
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The Resistor Code
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The Capacitor
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Capacitance is the ability to store an electric field.
The basic unit of capacitance is the Farad (abbreviated "F").
In a capacitor, there are two electric plates separated by an
insulating material As the current flows, electrons build up on
one plate. At the same time, electrons flow out of the other
plate.
Eventually, the capacitor is completely "charged up" and no
more current will flow.
With direct current, a capacitor would eventually become
charged up and no more current would flow through the
capacitor.
With alternating current, and the current switched directions
backwards, then the capacitor would start to "discharge" as
the current began to flow the opposite direction.
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Milli, Micro, Nano, Pico,
1 mili = 1/1,000th
or .001 times the unit. (10-3)
1 micro = 1/1,000,000
or 0.000 001 times the unit (10-6 )
1 nano = 1/1,000,000,000
or 0.000 000 001 times the unit (10-9 )
1 pico = 1/1,000,000,000,000
or 0.000 000 000 001 times the unit (10-12 )
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Digital Multipliers
Table 1 Digit multipliers
Multiplier (this times the first two digits
!gives you the value in Pico-Farads)
Third digit
0
1
1
10
2
100
3
1,000
4
10,000
5
100,000
6 not used
7 not used
8
.01
9
.1
A capacitor marked 104 is 10 with 4 more zeros or 100,000pF which is
otherwise referred to as a .1 uF capacitor.
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Electro-Magnet
•We can create an electro-magnet by wrapping many turns of wire
on a core, then causing an electrical current to flow through this coil
of wire.
•When the battery is not connected, there is no current flow, and
therefore no magnetic field.
•When the battery is connected, current flows through the coil, and
a magnetic field is created,
•The magnetic field curves around from one end of the coil to the
other.
–The field is strongest at the ends of the coil, and gets weaker as we get
farther away.
–We call the two ends of the coil the "poles"., one is "North" and the other is
"South“
– When the battery is not connected, there is no current flow, and therefore no
magnetic field.
–When the battery is connected, current flows through the coil, and a magnetic
field is created, as shown by the red lines.
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