Download Atomic Structure Review

Please use this electricity information packet
to answer the questions on your electricity
assignments. Do not use your book!
Atomic Structure Review
Low mass particles called electrons orbit a very
dense nucleus composed of two types of high mass
particles called neutrons and protons. Relative to
the size of the particles, the distance between the
nucleus and the orbiting electrons is very large.
Atoms are mostly empty space.
Electrons have a negative charge and very low
mass compared to neutrons and protons.
Electrons are arranged in layers called energy
levels at different distances from the nucleus of their
atoms. There are limits to how many electrons can
be in each energy level.
Protons have a positive charge and very high mass
compared to electrons.
Protons are packed closely together with neutrons
in the nucleus.
Neutrons have no charge and very high mass
compared to electrons.
Neutrons are packed closely together with protons
in the nucleus.
Protons and neutrons have nearly the same mass,
It would take more than 1,800 electrons to balance
the mass of one proton or one neutron.
The protons and neutrons are packed very close
together compared to the electrons in the energy
levels. Usually, positively charged particles
strongly repel each other, but in the nucleus of
atoms another force called the “strong force”
overpowers the force of repulsion and keeps the
protons close together. The strong force is provided
by smaller particles known as “gluons”.
The three main particles (protons, neutrons & electrons)
are made of smaller particles. Protons and neutrons are
made of quarks. Electrons are made of leptons. Many
other small particles play important roles in the nucleus.
If you wish to know more about these particles and their
function, research the term “particle physics” on the
Internet or in a modern encyclopedia.
Conductors & Insulators
In atoms of metallic elements, (3 electrons or less
in the outer energy level) like the lithium atom
shown above, the outer electrons are weakly held
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compared to atoms of elements that have 4 or more
electrons in the outer energy level. Because of this,
Lithium - the simplest metallic
atom.
the electrons in a solid or liquid piece of metal share
their outer electrons rather than keeping them in
orbits around particular atoms. The outer electrons
move randomly from atom to atom within the piece
of metal. This property allows metals to “conduct”
an electrical current easily. Therefore, metals are
known as good conductors of electricity.
Materials called insulators do not conduct
electricity easily because the outer electrons in their
atoms are strongly attracted to each individual atom
and cannot easily be made part of an electrical
current.
Electricity
Electricity is usually thought of as electrons that
are moving or have moved from one atom to
another. If there is a continuous stream of
electrons, they are described as an electrical
current. If an excess of electrons have collected on
an object, but are not moving they are described as
a static electricity.
Static Electricity & Charging
Atoms are electrically “neutral”. This means that
the positive charges (protons) are balanced exactly
by an equal number of negative charges (electrons).
A neutral object that gains electrons becomes
negatively charged.
When a neutral object loses electrons, it becomes
positively charged.
If the charged object was originally a single atom,
molecule or small group of atoms the charged
particle is referred to as an ion.
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A large object can acquire a considerable “charge”.
Lightning is the result of a large accumulation of
charge. Lighting is one of the most dramatic forms
of electrical discharge.

Smaller electrical discharges can be observed when
static electricity causes a spark to jump from one
object to another (like when we pull a sweater off
over our head). Electrical discharges are the result
of “grounding” an object after charge builds up. If
the object is “grounded” continuously, charge will
not build up on the object and electrical discharge
will be prevented. Lightning rods serve this
purpose by draining off charge as it starts to
accumulate on buildings and towers. Lightning
rods are not designed to conduct lightning
discharges to the ground. Lightning carries enough
electrical current to vaporize large diameter copper
wire.

Current Electricity
Current electricity is subdivided into two types,
DC and AC. All current electricity in solids can be
described as a flow of electrons.
DC (direct current) flows only in one direction…
from a negatively charged place to a positively
charged place. In a battery powered circuit the
electrons will flow from the negative terminal to the
positive terminal when connected with a conductor.
This would be a “short circuit” and could ruin the
battery, cause the battery to explode or cause the
conductor to get hot enough to start a fire. You will
learn more about circuits later.
AC (alternating current) reverses direction many
times per second. Household electricity is AC. AC
has one big advantage over DC. We can raise and
lower the voltage using transformers. We will
discuss how this is possible and why it is necessary
later in this unit.
Electrical Circuits
Electrical circuits are pathways for electrons.
 Complete Circuits - Complete circuits give
electrons an unbroken pathway from the source
(battery, etc.) through the conductors and back
to the source.
Safe Circuits - electrons in the circuit
travel through an electrical device that
uses their energy safely (light bulb,
motor, etc.) and back to the electron
source.
Short Circuits - electrons travel in a
direct pathway from the source directly
back to the source without passing
through a device that uses the energy
safely.
 Whenever electrons flow in a
conductor, part of their energy is
converted to heat energy.
 Short circuits can cause
damage to the circuit wiring
and other components through
overheating and may cause
serious burns or fires to occur.
All circuits have two possible conditions.
 In the closed condition the circuit is a
“complete” circuit and is said to be “on”.
 In the open condition the circuit is
“incomplete” or “broken” and is said to
be “off”.
Electricity does not flow through an open circuit.
Properly constructed electrical circuits have several
common features. They must have
 a source of power (AC or DC
power supply),
 conductors (pathways for the
electrons), and
 some sort of device designed to
use the electrical energy
(sometimes called the “load”).
Two other very common features are switches (to
open and close the circuit) and fuses or circuit
breakers (to protect the circuit from overheating).
All of the components of a circuit must be designed
to safely handle the amount of current flow required
by the circuit. It is necessary to consider the
voltage and amperage (or wattage) ratings of all
components before installing them in a circuit.
Failure to use components with sufficient rating will
result in damage to the circuit and may cause one or
more components of the circuit to overheat.
Overheated circuits are responsible for many
vehicle and building fires.
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resistance for the current to reach your
heart or brain. However, some people
have suffered tissue damage while using
our lab equipment in an inappropriate
manner.
 Several students have “tested”
the voltage by placing the power
clips on their tongue. This
resulted in some tissue
destruction.
 One student connected the power
clips to his braces. The result
was the death of one of his teeth.
 Another student connected the
power clips to his earring. The
student suffered considerable
pain in his left earlobe for several
days.
Two Basic Electrical Circuit Classes
All electrical circuits can be classified as series or
parallel circuits (or a combination of the two).
In series circuits, the current passes through devices
in sequence (first through one, then through a
second, etc.). If any of the devices fail to conduct
the current, all current flow stops in the circuit.
In parallel circuits, the current flows through two
or more devices simultaneously. If one device fails,
the current will still flow through the other
device(s).
Safety
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Do not experiment with household
current (110-240vac).
All of the components of a circuit must
be designed to safely handle the amount
of current flow required by the circuit.
It is necessary to consider the voltage,
amperage and wattage ratings of all
components before installing them in a
circuit.
If a short circuit will cause overheating,
a fuse or breaker of the proper rating
must be used to prevent damage (Low
current circuits like flashlights and watches
usually do not require fuses or circuit
breakers).


Failure to use components with
sufficient rating will result in damage to
the circuit and may cause one or more
components of the circuit to overheat.
Overheated circuits are responsible
for many vehicle and building fires.
Our Lab Electricity
 The electricity we use in the electricity labs in
this class is direct current electricity (DC).
We do not experiment with common household
electricity because it is deadly. More people
are killed with common household (110-125
volt AC) current than any other form of
electricity.
 Under most circumstances, the DC
electricity that we use in our labs will
not hurt you. Your body has too much
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The voltage at the source (a wet cell, deepcycle, RV/Marine battery) is about 13.8 volts.
The voltage at your stations is about 11 - 13
volts.
Your station is protected by a 3.1 ampere circuit
breaker and controlled by a SPST (single-pole
single-throw) switch.
When the circuit is closed (switch is “on”), the
LED (light emitting diode) beside the switch
will light up.
When you touch the power clips together, a
“short circuit” will result which will cause your
breaker to “break” or “trip”.
The breaker can be “reset” by pushing the reset
button.
If two or more stations are “short circuited” at
the same time, the main 10 amp circuit breaker
will trip. If this occurs too often, the lab
exercise will be discontinued.
A 10 A circuit breaker near the battery protects
the entire DC lab circuit complex.
Terminals
A terminal is a place where electrons (or
other charged particles) can enter or
leave an electrical component
(battery, switch, light bulb, electrical
outlet, etc.).
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Negative Terminals - Electrons flow out
of this terminal on batteries and other
manmade sources of DC electricity.
Positive Terminal - Electrons flow into
this terminal on batteries and other
manmade sources of DC electricity.
Appliances (radios, GPS units, LED
devices, etc.)
Negative Terminal - This terminal must be
connected to the negative terminal of the
energy source. Electrons flow into this
terminal from the energy source.
Positive Terminal - This terminal must be
connected to the positive terminal of the
energy source. Electrons flow out this
terminal back to the energy source.
Classifications of Electricity
Static electricity is an accumulation of electrons or
other charged particles can produce a "static
charge" which when discharged becomes
current electricity of short duration. This is
often referred to as "static discharge".
For example, a wool sweater will lose some
of its electrons to a cotton shirt because the
atoms in the cotton have a stronger
attraction for the electrons in the wool. This
results in the sweater having a positive
charge and the shirt having a negative
charge. When the shirt and sweater are
separated, some of the electrons are pulled
back to the sweater causing “static
discharge”. Before the shirt and sweater are
separated, they have an attraction for each
other because of the difference in charge.
This attraction has come to be known as
“static cling”. Some fabric softeners are
formulated to provide a very thin coating of
insulating chemical on the fibers of clothing.
This coating prevents or reduces the transfer
of electrons or ions and effectively prevents
“static cling”.
Other static electricity events can be seen in
rooms with dry air and carpeted floors. A
static charge can be collected as we walk
along the carpet and discharged later when
we touch something that is “grounded” (like
an electrical appliance that is plugged into a
grounded outlet). Although they are short
lived, static discharges that take place in our
houses can be thousands of volts (enough to
zap your computer or CD player if they are
not built properly.).
Another example of static discharge is
lightning. Lightning is static discharge
between clouds or between clouds and earth.
Lightning bolts have millions of volts of
force pushing (or pulling) them. Electrons
and ions (larger charged particles) can be
transferred between clouds or between
clouds and the ground resulting in a
“charge” being built up in both places.
When the difference between the two
opposite charges becomes great enough, a
massive flow of electrons (lightning) occurs
between the two objects.
Current electricity is a flow of electrons...
electrons moving from one place to another.
The electrons are forced to move by the
attraction or repulsion of protons or other
electrons. Current electricity is generally
classified as DC (direct current) or AC
(alternating current).
DC (direct current) is electricity that flows
only in one direction. Static discharge
electricity is DC. Electricity produced by
chemical (voltaic) cells, batteries, and solar
cells is also DC.
AC (alternating current) gets its name
from the fact that the electrons reverse
direction many times per second. The
electricity we use in our homes is AC.
There are many other sources for AC such
as radio waves, light waves, microwaves and
radar waves.
SOURCES OF ELECTRICITY
DC (direct current) is the most “natural”
form of electricity. Every time we
experience the spark or shock from the
discharge of a static electricity charge we
are seeing or feeling direct current
electricity. Of course, lightning is our most
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powerful source of DC. Other sources of
DC are chemical cells, photovoltaic cells,
fuel cells and batteries made from a
combination of cells.
AC (alternating current) occurs in nature,
but the alternating current we use the most is
produced at electrical power plants by the
use of “alternators” turned by steam power.
CONDUCTORS, INSULATORS, RESISTORS
CAUTION!! Anything will conduct
electricity if the voltage is high enough...
even air!
A conductor is a material that allows electrical
charges to pass through it easily. The most
common conductors are metals. In solid
conductors, electrical current is in the form
of electrons, but in liquids, gases and
plasmas the current is a flow of charged
particles called ions.
Metallic conductors are composed of atoms
that have a weak attraction for their outer
electrons. The outer electrons of metallic
atoms are free to roam around from atom to
atom in a sort of “electron soup”. When
connected in a complete circuit to a voltage
source (battery, generator, etc.), the free
electrons are forced to flow in an electrical
current away from the negative terminal,
through the circuit and back to the positive
terminal of the voltage source.
Electrolytic solutions like salt water or
water with a lot of dissolved minerals are
better conductors of electricity than pure
water because they contain more ions.
Ordinary drinking water does not conduct
low voltage electricity very well, but will
conduct household electricity well enough to
kill you.
Insulators are usually composed of atoms that have
a strong attraction for their valence (outer)
electrons making it difficult to move them
from atom to atom. In some insulators, the
electrons are not free to move because they
are involved in a strong chemical bond with
other atoms.
Resistors are made of materials that reduce the flow
of electrons from atom to atom. This
“resistance” occurs because of a strong
attraction between the nucleus of the atoms
in the material and the passing electrons.
VOLTAGE, AMPERAGE, AND RESISTANCE
Voltage refers to the electrical "force" that moves
the electrons. It is sometimes referred to as
"electrical potential" or "electromotive
force" (EMF). The metric unit used to
measure voltage is the volt (V).
The speed of electricity through the best of
conductors is close to 300,000,000 meters
per second (about 186,000 miles per
second).
Normal flashlight voltages range between
1.5 VDC and 18 VDC. A car battery
usually produces 13 to 15 VDC. In case you
haven't figured it out already, VDC means
"volts direct current". House electricity
usually is moved along with a force of 110125 VAC (volts alternating current). Some
household appliances (water pumps, clothes
dryers, stoves, air conditioners, etc.) may
need 220-240 VAC, which is also available
at your main electrical panel.
You should remember that more people are
killed with 110-120 VAC electricity than
any other voltage. It is dangerous if not
used safely. KEEP YOURSELF OUT OF
THE CIRCUIT!!
Amperage refers to the "current" or number of
electrons flowing past a point each second.
The metric unit used to measure electrical
current is the ampere (A) and is equal to
6.24 x 1018 electrons
(6,240,000,000,000,000,000) passing a
point in a second. In order to make things
easier we call this number of electrons a
coulomb (C). So, one coulomb per second is
equal to one ampere. (1C/s=1A). The term
ampere is usually shortened to amp.
Excessive current flow through a
conductor or device can cause overheating.
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Resistance is a term used to describe how much a
material restricts the flow of electricity.
Resistance to the flow of electricity comes
from the attractive force of the protons in the
nuclei of the atoms making up the material.
A strong attraction between the protons and
passing electrons produces higher resistance
to electrical current (the flow of electrons).
The metric unit used to measure electrical
resistance is the ohm. The symbol for the
ohm is the Greek letter omega .
Resistance causes electricity to be
transformed into heat and, in most cases
represents an unintentional loss of energy
(inefficiency).
Some materials have a very low resistance
to electric current and are called
CONDUCTORS. Conductors are made of
materials in which electrons can easily be
made to jump from atom to atom.
Materials with a very high resistance are
called INSULATORS.
In order for electrons to "flow" in a material,
the outer electrons of the atoms making up
the material must be "loose", or weakly
attracted by the nuclei of the atoms making
up the material.
We have yet to discover a material that is
the perfect insulator or conductor. All
materials have some resistance and some
conductance (the opposite of resistance). If
the voltage is high enough, anything will
conduct electricity.
Resistors are devices specifically designed
to "resist" or restrict the flow of electrons.
Resistors are primarily used in electronic
devices.
Note: Some resistors are “variable resistors”.
That means that the resistance can be
changed by a rotary or slide mechanism.
Another name for a variable resistor is
potentiometer or “pot”. Volume controls,
light dimmers & motor speed controls are all
variable resistors.
Fuses & Circuit Breakers
Overheated electrical components may
result in an electrical fire or other damage to
the device. Fuses and circuit breakers are
designed to interrupt the flow of current if it
becomes excessive. Fuses have a metal strip
inside that melts when the circuit is
overloaded. Circuit breakers have an
automatic thermal or magnetic switch that
turns the circuit off when too much current
is being used. Fuses are cheaper than circuit
breakers, but they are not reusable. Because
fuses are easily replaced, people without a
good knowledge of electricity can
accidentally cause a hazardous situation by
replacing a fuse with one that has more
current carrying capacity. Using a larger
fuse is dangerous because the wiring may
not be able to safely conduct the same
amount of current as the larger fuse.
Since circuit breakers are not easily or
cheaply replaced, they are considered to be a
safer device for protecting home circuits.
Wire size must always be considered
when working with electricity. Larger
diameter wire of the same material can
conduct more current than smaller wire.
Wire size is rated with the “gauge” system.
Larger wire will conduct electricity better
with less loss of voltage due to resistance.
Most house wiring is 12 gauge (12 AWG).
Larger wire (10 ga.) is used for clothes
dryers and hot water heaters. Even larger
wire (8 ga.) is used for electric stoves.
Extension cord wire is usually 18 ga. or 16
ga. and cannot safely conduct as much
current as house wiring. A short extension
cord is preferable over a long one because as
the cord length increases so does the energy
loss due to resistance. Extension cords with
larger wire size are preferable because they
will conduct electricity with less loss of
energy due to resistance. Never use a fuse
or circuit breaker with a higher amperage
rating than that of the wire in the circuit.
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Electricity From Cells & Batteries (DC)
DC (direct current) is electricity that flows
only in one direction. Static discharge
electricity is DC. Electricity produced by
chemical (voltaic) cells, batteries, and solar
cells is also DC.
Some DC devices (radios, TVs, CB radios,
CD players, etc.) can be damaged if the
current flows the wrong way. To prevent
damage from “polarity reversal”, some
manufacturers insert a diode in series with
one of the power socket wires. Diodes will
allow electricity to flow only in one
direction. If a device is “diode protected”
against polarity reversal, no damage will
occur if the positive and negative power
leads are reversed. The device simply will
not work because the diode prevents any
current flow.
Batteries are made up of “cells”. Normally,
when we think of cells and batteries we
think of the type used in flashlights, portable
radios, cars & trucks, garage door openers,
etc. These are “electrochemical” cells and
batteries. A single electrochemical cell may
also be known as a “voltaic” cell (named
after Allesandro Volta, the Italian physicist
who invented the “voltaic cell” and “voltaic
pile”). The term “wet cell” refers to the
liquid electrolyte used in the cells of most
automotive, marine and aircraft batteries.
“Dry cells” contain electrolyte in solid or
paste form.
Normal flashlight voltages range between
1.5 VDC and 18 VDC. A car battery
usually produces 13 to 15 VDC.
Different voltages in batteries are achieved
by connecting different numbers of cells in
series with each other. This means the
negative terminal of one cell is in contact or
connected to the positive terminal of the
next cell.
Different current ratings (amperage) and
charge holding capacities are achieved by
connecting different numbers of cells in
parallel with each other. This means the
negative terminal of one cell is connected to
the negative terminal of the next cell.
Likewise, the positive terminals of the cells
are all connected to each other.
If both higher voltage and higher current
(amperage) ratings are required, a seriesparallel battery can be constructed with
several series batteries can be connected in
parallel with each other (the negative
terminals of all the batteries connected
together and the positive terminals of all the
batteries hooked together). Most automotive
batteries are series-parallel construction.
We have all used cells and batteries. The
common designations of “D”, “C”, “AA”
and “AAA” all apply to the different sizes of
cells even though they are improperly
labeled as batteries on the package.
Miniature flashlights often operate with a
single cell. Larger flashlights may use six
cells or more. The operating voltage of a
flashlight that takes a single “AA” or
“AAA” cell is about 1.5 volts. The operating
voltage of a 2-cell flashlight is usually about
3V and a six-cell flashlight normally has an
operating voltage of 9V.
Photovoltaic cells (also known as solar
cells) are devices that, when connected as
part of a complete circuit, produce direct
current electricity when exposed to light.
Up to the limits of the device, an increase in
light intensity will increase electrical current
available for the circuit. Like the cells we
use in flashlights, photovoltaic cells may be
connected in series or parallel or seriesparallel to produce higher voltages and
currents. Like automotive batteries,
photovoltaic arrays (batteries) are usually a
large number of cells connected in a seriesparallel configuration.
Fuel cells, like the common flashlight
cell are also electrochemical devices, but
they produce electricity by using a fuel
that may be replenished. Natural gas
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(methane) is often used as the fuel in
earth-bound applications. The United
States Space Shuttle fleet uses fuel cells
powered by hydrogen to produce
electricity and water.
Electricity From Electrical Power
Companies (AC)
AC (alternating current) gets its name
from the fact that the electrons reverse
direction many times per second. The
electricity we use in our homes is AC.
There are many other sources for AC such
as radio waves, light waves, microwaves and
radar waves.
Electric company generators (often called
alternators), which get their energy from
high-pressure steam or other gases, produce
most AC. Steam is produced by boiling
water with a coal or oil-burning boiler. The
steam is allowed to build up pressure before
it is released through nozzles to spin highspeed turbines. Steam driven turbines are
connected to the alternators that produce the
electricity.
How Electricity Is “Generated”
When a magnetic field and a conductor
move across each other, electrons are forced
to move along the conductor if it is a part of
a complete circuit. One of the two, either
the magnetic field or the conductor, must
be moving in order to force the electrons
into motion.
Whenever electricity starts to flow in a
conductor, a magnetic field expands or
“grows” outward from the conductor. In
wires the magnetic field surrounds the wire
for its entire length as long as the current of
electrons is flowing. When the electrons
stop flowing, the magnetic field collapses
back into the wire. Keep in mind that this
expanding and collapsing magnetic field
is a magnetic field in motion (but only
while it is either expanding or collapsing).
How does the magnetic field move
electrons? If we imagine a flexible, clear
plastic hose full of steel marbles, we can see
the action of a magnetic field. If we hook
the ends of the tube together to form a
continuous loop and if a strong enough
magnet is used, the steel marbles can be
made to move around the loop without
actually touching them. As we move the
magnet along the outside of the tube, the
magnetic field forces the marbles to move
along the loop with the magnet. Alternating
current (AC) is generated in much the same
way.
Inside generators are giant magnets that spin
near large coils of wire. When the magnetic
field from the magnets moves through the
wires it causes electrons to move in the
wires that lead from the coils to the
electrical transmission lines outside.
Getting The Electricity To Us
One of the problems in the early days of
electrical power generation was resistance.
Remember that resistance is the term used to
describe forces within the atoms that oppose
the flow of electrons through a conductor.
Mr. Edison’s first commercial generators
produced DC electricity. Those customers
close to the generating plant had plenty of
voltage, but those who lived at the end of the
line had much lower voltage (dimmer
lights). Mr. Edison’s solution was to build
lots of small power plants. Mr.
Westinghouse had a better plan.
Thanks to Mr. Westinghouse and his
employees, the electric power companies
now use alternating current. They use AC
because its voltage can be "stepped up" or
"stepped down" by the use of devices
known as "transformers". This feature of
AC gives us many advantages. The main
advantage is that every house in the United
States can receive pretty much the same
voltage electricity from the power company.
Due to voltage drops caused by resistance in
the power lines, this convenience was not
possible with DC power plants. Of course,
this means that “step-up” transformers
must be located in many places between the
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power company generators and our
communities in order to counteract the
effects of resistance in the lines. Near our
homes and businesses are “step-down”
transformers to give us the lower voltage
required to run our appliances.
Transformers
Transformers are devices containing two or
more coils of wire that are very close
together, but not physically connected. The
coils of wire are wrapped around an iron or
iron alloy core to make the transformers
more efficient.
The wire making up each coil is coated with
a very tough, high voltage insulating
material to prevent "short circuits" due to
contact between the wires. Each coil has
hundreds or even thousands of "turns" or
wraps of wire. Electric power company
transformers are located outside our homes.
They can be seen high on utility poles or
mounted in large, insulated boxes on the
ground.
Back at the electric power company, their
alternator is connected to one of the coils
(the primary coil) in the first “step-up”
transformer outside the power generation
building. When the power company
alternators are in operation, the other coils
inside the transformer (secondary coils) are
subjected to the expanding and contracting
magnetic field caused by the alternating
current. This expanding and contracting
magnetic field causes electrons to flow in
the secondary coils of wire even though they
are not physically connected to the primary
coil.
Here is the advantage of AC. If the
unconnected coil (the secondary coil) has a
different number of "turns" than the
primary coil, the voltage will be different
than it is in the primary coil.
More turns on the primary than on the
secondary will cause the voltage to be
lowered. More turns on the secondary than
on the primary will cause the voltage to be
raised.
The transformer on the pole near your house
is a "step down" transformer because it
lowers the voltage from thousands of volts
to about 240 volts.
Other examples of "step down"
transformers are the “power cubes” or
“power supplies” that allow us to operate
portable CD players, radios, etc., on
household electricity. Inside the black
plastic boxes are coils of wire that make up
a “step down” transformer and a diode
circuit that converts the AC to DC.
Note: These devices are using electricity any
time they are plugged into the wall outlet
even if the CD player or other device is not
turned on. When the transformer is plugged
in electricity constantly flows through the
coils of wire inside the box. The resistance
of the wire causes the electricity to be
converted to heat energy even nothing is
being powered by the unit.
Most televisions and microwave ovens have
a “step up” transformer in the back that
boosts the voltage from 120 V to 30,000 V
or higher. Do not disassemble these
appliances or poke things inside the
ventilation holes! The electricity stored in
the television and microwave oven circuits
can kill you!
Electricity Information Packet
Pg 10
1995 Sci-Ed Services
Circuit Diagram Symbols
Circuit diagrams are used to illustrate the
design of electrical circuits. These diagrams
(often called “schematic diagrams” or just
“schematics”) use symbols for various
components rather than a drawing that
closely resembles the actual appearance of
the component. Switches, fuses, conductors,
lights, etc., come in thousands of different
sizes and shapes. The use of circuit symbols
saves a lot of drawing time and space when
designing a circuit. Some common circuit
symbols are shown below.
CONDUCTORS MUST BE DRAWN AS
STRAIGHT LINES OR STRAIGHT LINES
WITH 90o TURNS.
2 conductors, crossing each other, but not
electrically connected.
2 conductors that are electrically connected.
A single cell - 1.5 volts
A 6 volt battery consisting of four 1.5 v cells
connected in series.
A 1.5 volt battery consisting of three 1.5 v
cells connected in parallel.
-
Heavy dots are
TERMINALS
+
series
+
+
A 2-terminal switch known as a SPST
(single pole, single throw)
A 3-terminal switch known as a SPDT
(single pole, double throw)
“open” position
“closed” position
“closed” (on)
“open” (off)
A fuse or circuit breaker.
An incandescent lamp (solid wire filament).
A diode.
A resistor.
parallel
Electricity Information Packet
+
+
1.5 V
1.5 V
1.5 V
1.5 V
A 1.5 volt battery - 4 cells in parallel
-
A 1.5 volt battery - 4 cells in parallel
-
+
+
A 6 volt battery - 4 cells in series
1.5 V
1.5 V
1.5 V
1.5 V
+
1.5 V
1.5 V
1.5 V
1.5 V
A 6 volt battery - 4 cells in series
+
A 6 volt battery - 4 cells in series
+
1.5v
cell
1.5v
cell
_
+
_
1.5v
cell
_
“Incomplete Circuit”
(“Open Circuit”)
(”Off”)
“Complete Circuit”
(“Closed Circuit”)
(”On”)
_
1.5v
cell
+
_
Short Circuit
1.5v
cell
+
2-Cell Flashlight Circuit
(3 v)
+
A complete circuit with a
3v battery, a lamp, a fuse
and a switch in the closed
position.
Pg 11
1995 Sci-Ed Services
+
An incomplete circuit with
a 3v battery, 2 lamps in
series, a fuse and a switch
in the open position.
+
A complete circuit with a
3v battery, 3 lamps in
parallel, a fuse and a switch
in the closed position. Note
that the fuse protects the
entire circuit.
Electricity Information Packet
Pg 12
1995 Sci-Ed Services
Dome Light
Battery
-
+
Light Switches
Positive wires return
electrons from the
different devices to the
battery.
Tail Light
Fuse Block
Cable from
negative terminal
bolted to the metal
frame of the truck.
In a truck (and other vehicles), only the positive
side of the circuit is wire. The conductor for the
negative side of the circuit is the metal frame
and body of the truck.
Electricity Information Packet
Pg 13
1995 Sci-Ed Services
The ratings in the following tabulation are those permitted by the National Electrical Code for flexible
cords and for interior wiring of houses, hotels, office buildings, industrial plants, and other buildings.
The values are for copper wire. For aluminum wire the allowable carrying capacities shall be taken as
84% of those given in the table for the respective sizes of copper wire with the same kind of covering.
(Source: Handbook of Chemistry & Physics, 74th Edition, 1993-94, pg. 15-29)
Size
A.W.G.
18
16
14
12
10
8
6
5
4
3
2
1
0
00
000
Diameter
of Solid
Wires Mils
(.001 inches)
40.3
50.8
64.1
80.8
101.9
128.5
162.0
181.9
204.3
229.4
257.6
289.3
325.0
364.8
409.6
Rubber
Insulation
Amperes
3*
6*
15
20
25
35
50
55
70
80
90
100
125
150
175
Varnished
Cabric
Insulation
Amperes
18
25
30
40
60
65
85
95
110
120
150
180
210
Other
Insulations
and Bare
Conductors
Amperes
6**
10**
20
30
35
50
70
80
90
100
125
150
200
225
275
* The allowable carrying capacities of No. 18 and 16 are 5 and 7 amperes respectively, when in flexible
cords.
** The allowable carrying capacities of No. 18 and 16 are 10 and 15 amperes respectively, when in cords
for portable heaters. Types AFS, AFSJ, HC, HPD, and HSJ.
Resistance in wire (values are for wire that is 1000 feet in length at 20oC.
Gauge
Ohms
Ohms
Ohms
Gauge
Ohms
Ohms
No.
per 1000 per 1000 per 1000
No.
per 1000 per 1000
feet
feet
feet
feet
feet
o
o
o
o
@0 C
@ 20 C
@ 50 C
@0 C
@ 20oC
10
.9203
.9989
1.117
22 14.87
16.14
12
1.463
1.588
1.775
24 23.65
25.65
14
2.327
2.525
2.823
26 37.61
40.18
16
3.700
4.016
4.489
28 59.80
64.90
18
5.883
6.385
7.138
30 95.08
103.2
20
9.355
10.15
11.35
32 151.2
164.1
Ohms
per 1000
feet
@ 50oC
18.05
28.70
45.63
72.55
115.4
183.4
Electricity Information Packet
Pg 14
1995 Sci-Ed Services
SUMMARY
Atoms are composed of these “subatomic
particles”…
In the nucleus
- protons (+ charge)
- neutrons (no charge)
- and other smaller particles
Orbiting the nucleus in the electron cloud are
the electrons ( - charge)
Atoms are electrically balanced or neutral
because they have an equal number of protons
and electrons.
When atoms become electrically unbalanced by
the loss or gain of an electron they are called
ions.
Particles with like charges repel each other.
from the source, through the devices and back to
the source.
A short circuit bypasses the main electrical
device(s) in a circuit. This is a dangerous form
of complete circuit that allows the electricity to
flow directly from the source through the wires
and directly to the source without going through
the intended device(s). Short circuits cause
dangerous overheating of the wires and power
source and may cause a fire or damage to the
circuit.
Voltage - also called electrical potential , potential
difference or electromotive force (EMF). Voltage
is often thought of as "electrical pressure".
When voltage is increased more electrons
move through the circuit over a given
period of time.
Particles with unlike charges attract each other.
Electron flow - occurs when outer electrons of
atoms are forced to jump to neighboring atoms
either by repulsion or attraction.
Conductors - materials made of atoms, which
have a weak attraction for their outer electrons.
These materials have a low resistance to the flow
of electricity.
Insulators - materials made of atoms, which have
a strong attraction for their outer electrons.
These materials have a high resistance to the
flow of electricity.
Circuits – The two main classes of circuits are
parallel and series. In a series circuit, the
current flows first through one device and then
through another. In a parallel circuit the
current is split and goes simultaneously to two or
more main devices.
A complete (unbroken or closed) circuit is one
that has a continuous pathway for the electricity
to travel from the source, through the devices
and back to the source.
An incomplete (broken or open) circuit does not
have a continuous pathway for the electricity
The metric unit used to measure voltage is the
volt. Two symbols are used for voltage.
- in electrical formulas E = volts
- in all other work V = volts
Current - the quantity of electrons flowing past a
point during a given unit of time.
The metric unit used to measure current is the
ampere (amp).
1 amp is equal to the
passage of 6.24 x 1018 electrons in 1 second (1
coulomb/sec).
Two units are used to express current:
- in electrical formulas I = amperes (current)
- in all other electrical applications A = amperes
Direct Current
Electrons flow constantly in one direction.
Alternating Current
Electrons are forced to reverse their direction of
travel many times per second.
Two reversals (alternations) equal one complete
cycle.
A current that goes through one cycle
each second is said to have a frequency of
1 Hz.
Electricity Information Packet
Pg 15
1995 Sci-Ed Services
A current that undergoes more cycles per
second than another current is said to
have a higher frequency.
Resistance - all materials have some resistance to
the flow of electrons because the positively
charged nuclei of the atoms exert a holding force
on the electrons, which opposes the voltage
(electromotive force). This holding action results
in a conversion of electrical energy into heat
energy. All materials will undergo some
“resistance heating” when subjected to electrical
current. Some materials, like the wires in
toasters, produce useful heat. In other materials,
like the filaments in light bulbs and the wiring in
transformers produce heat which is often
wasted.
"Conductors" have less resistance than
"insulators".
Resistance to electrical current causes
heating of the conducting material.
The metric unit used to measure electrical
resistance is the ohm. Resistance is expressed by
two symbols:
- in formulas R= ohms (resistance)
- in most other electrical applications = ohm
More about conductors and insulators
All conductors have some resistance to the flow
of electrons. The "perfect" conductor has not
been discovered yet.
All insulators have a breakdown voltage at which
electrons begin to flow. The "perfect" insulator
has not been discovered yet.
Electrical components are rated according to the
amount of voltage and current they can handle.
Ohm's Law
Ohm stated the relationship between voltage,
current and resistance somewhat like this:
It takes 1 volt to push 1 amp through a resistance
of 1 ohm.
or E=IR
Ohm's Law Formulas
The basic formula (E=IR) can be rewritten to
solve for current and resistance as well as for
voltage.
E
I =
R =
R
E
I
To calculate the amps used by a device, use the
formula
I=
P
or
amps = watts
voltage
E
amps = I or A
voltage = E or V
watts = P or W
To calculate the watts used by a device, use the
formula
P = IE
or
watts = amps X volts