


                      FUNDAMENTAL CONCEPTS OF ELECTRICITY

    The word "electric" is actually a Greek derived word meaning AMBER.  Amber
is a translucent (semitransparent) yellowish mineral, which, in the natural
form, is composed of fossilized resin.  The ancient Greeks used the words
"electric force" in referring to the mysterious forces of attraction and
repulsion exhibited by amber when it was rubbed with a cloth.  They did not
understand the fundamental nature of this force.  They could not answer the
seemingly simple question, "What is electricity?".  This question is still
unanswered.  Though electricity might be defined as "that force which moves
electrons," this would be the same as defining an engine as "that force which
moves an automobile."  The effect has been described, not the force.

Electricity may be defined as that force which moves _________.
ANSWER ELECTRONS


    Presently little more is known than the ancient Greeks knew about the
fundamental nature of electricity, but tremendous strides have been made in
harnessing and using it.  Elaborate theories concerning the nature and behavior
of electricity have been advanced, and have gained wide acceptance because of
their apparent truth and demonstrated workability.
    From time to time various scientists have found that electricity seems to
behave in a constant and predictable manner in given situations, or when
subjected to given conditions. These scientists, such as Faraday, Ohm, Lenz, and
Kirchhoff, to name only a few, observed and described the predictable
characteristics of electricity and electric current in the form of certain
rules.  These rules are often referred to as "laws."

Electricity behaves in constant and ___________ ways that are described by rules
that are often referred to as "laws."
ANSWER PREDICTABLE








    Though electricity itself has never been clearly defined, its predictable
nature and easily used form of energy has made it one of the most widely used
power sources in modern time.  By learning the rules, or laws, applying to the
behavior of electricity, and by understanding the methods of producing,
controlling, and using it, electricity may be "learned" without ever having
determined its fundamental identity.

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                                  THE MOLECULE

    One of the oldest, and probably the most generally accepted, theories
concerning electric current flow is that it is comprised of moving electrons.
This is the ELECTRON THEORY.  Electrons are extremely tiny parts, or particles,
of matter.  To study the electron, therefore, the structural nature of matter
itself must first be studied. (Anything having mass and inertia, and which
occupies any amount of space, is composed of matter.)  To study the fundamental
structure or composition of any type of matter, it must be reduced to its
fundamental fractions.

One of the oldest, and probably the most generally accepted, theories concerning
electric current flow is that it is comprised of moving _________.
ANSWER ELECTRONS







Assume the drop of water in figure 1 (A) was halved again and again.  By
continuing the process long enough, the smallest particle of water possible -
the molecule - would be obtained.  All molecules are composed of atoms.
    A molecule of water (H2O is composed of one atom of oxygen and two atoms of
hydrogen, as represented in figure 1 (B). If the molecule of water were further
subdivided, there would remain only unrelated atoms of oxygen and hydrogen, and
the water would no longer exist as such.

All _________ are composed of atoms.
ANSWER MOLECULES





This example illustrates the following fact - the molecule is the smallest
particle to which a substance can be reduced and still be called by the same
name.  This applies to all substances - liquids, solids, and gases.
    When whole molecules are combined or separated from one another, the change
is generally referred to as a PHYSICAL change. In a CHEMICAL change the
molecules of the substance are altered such that new molecules result.  Most
chemical changes involve positive and negative ions and thus are electrical in
nature.  All matter is said to be essentially electrical in nature.

In a ________ change the molecules of the substance are altered such that new
molecules result.
ANSWER CHEMICAL
                                    THE ATOM

    In the study of chemistry it soon becomes apparent that the molecule is far
from being the ultimate particle into which matter may be subdivided.  The salt
molecule may be decomposed into radically different substances - sodium and
chlorine.  These particles that make up molecules can be isolated and studied
separately.  They are called ATOMS.
    The atom is the smallest particle that makes up that type of material called
an ELEMENT.  The element retains its characteristics when subdivided into atoms.
More than 100 elements have been identified.  They can be arranged into a table
of increasing weight, and can be grouped into families of material having
similar properties.  This arrangement is called the PERIODIC TABLE OF THE
ELEMENTS.

The atom is the smallest particle that makes up that type of material called
an _______.
ANSWER ELEMENT
    The idea that all matter is composed of atoms dates back more than 2,000
years to the Greeks.  Many centuries passed before the study of matter proved
that the basic idea of atomic structure was correct.  Physicists have explored
the interior of the atom and discovered many subdivisions in it.  The core of
the atom is called the NUCLEUS.  Most of the mass of the atom is concentrated in
the nucleus.  It is comparable to the sun in the solar system, around which the
planets revolve.  The nucleus contains PROTONS (positively charged particles)
and NEUTRONS which are electrically neutral.
    Most of the weight of the atom is in the protons and neutrons of the
nucleus.  Whirling around the nucleus are one or more smaller particles of
negative electric charge.  THESE ARE THE ELECTRONS.  Normally there is one
proton for each electron in the entire atom so that the net positive charge of
the nucleus is balanced by the net negative charge of the electrons whirling
around the nucleus. THUS THE ATOM IS ELECTRICALLY NEUTRAL.

Whirling around the nucleus are one or more smaller particles called _________.
ANSWER ELECTRONS









    The electrons do not fall into the nucleus even though they are attracted
strongly to it.  Their motion prevents it, as the planets are prevented from
falling into the sun because of their centrifugal force of revolution.   The
number of protons, which is usually the same as the number of electrons,
determines the kind of element in question.

In an atom the number of _______ is usual the same as the number of electrons.
ANSWER PROTONS







     Figure 2 shows a simplified picture of several atoms of different materials
based on the conception of planetary electrons describing orbits about the
nucleus.   For example, hydrogen has a nucleus consisting of 1 proton, around
which rotates 1 electron.  The helium atom has a nucleus containing 2 protons
and 2 neutrons with 2 electrons encircling the nucleus.  Near the other extreme
of the list of elements is curium (not shown in the figure), an element
discovered in the 1940's, which has 96 protons and 96 electrons in each atom.

The ______ atom has a nucleus containing 2 protons, 2 neutrons and 2 electrons.
ANSWER HELIUM






    The Periodic Table of the Elements is an orderly arrangement of the elements
in ascending atomic number (number of planetary electrons) and also in atomic
weight (number of protons and neutrons in the nucleus).  The various kinds of
atoms have distinct masses or weights with respect to each other.  The element
most closely approaching unity (meaning 1) is hydrogen whose atomic weight is
1.008 as compared with oxygen whose atomic weight is 16.  Helium has an atomic
weight of approximately 4, lithium 7, fluorine 19, and neon 20 as shown in
figure 2.

The atomic weight of oxygen is ____.
ANSWER 16









    Figure 3 is a pictorial summation of the discussion that has just been
presented.  Visible matter, at the left of the figure, is broken down first to
one of its basic molecules, then to one of the molecule's atoms.  The atom is
then further reduced to its subatomic particles - the protons, neutrons, and
electrons.

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     Subatomic particles are electric in nature.  That is, they are the
particles of matter most affected by an electric force.  Whereas the whole
molecule or a whole atom is electrically neutral, most subatomic particles are
not neutral (with the exception of the neutron).  Protons are inherently
positive, and electrons are inherently negative.  It is these inherent
characteristics which make subatomic particles sensitive to electric force.
    When an electric force is applied to a conducting medium, such as copper
wire, electrons in the outer orbits of the copper atoms are forced out of orbit
and impelled along the wire.  The direction of electron movement is determined
by the direction of the impelling force.  The protons do not move, mainly
because they are extremely heavy.  The proton of the lightest element, hydrogen,
is approximately 1,850 times heavier than its electron.  Thus, it is the
relatively light electron that is moved by electricity.

Subatomic particles are ________ in nature.
ANSWER ELECTRIC







    When an orbital electron is removed from an atom it is called a FREE
ELECTRON.  Some of the electrons of certain metallic atoms are so loosely bound
to the nucleus that they are comparatively free to move from atom to atom. Thus,
a very small force or amount of energy will cause such electrons to be removed
from the atom and become free electrons.  It is these free electrons that
constitute the flow of an electric current in electrical conductors.

It is the ____ _________ that constitute the flow of electric current in an
electrical conductor.
ANSWER FREE ELECTRONS


    If the internal energy of an atom is raised above its normal state, the atom
is said to be EXCITED.  Excitation may be produced by causing the atoms to
collide with particles that are impelled by an electric force.  In this way,
energy is transferred from the electric source to the atom.  The excess energy
absorbed by an atom may become sufficient to cause loosely bound outer electrons
to leave the atom against the force that acts to hold them within.  An atom that
has thus lost or gained one or more electrons is said to be IONIZED.  If the
atom loses electrons it becomes positively charged and is referred to as a
POSITIVE ION.  Conversely, if the atom gains electrons, it becomes negatively
charged and is referred to as a NEGATIVE ION.  An ion may then be defined as a
small particle of matter having a positive or negative charge.

An atom that has thus lost or gained one or more electrons is said to be
 _______.
ANSWER IONIZED



                   CONDUCTORS, SEMICONDUCTORS, AND INSULATORS

    Substances that permit the free motion of a large number of electrons are
called CONDUCTORS.  Copper wire is considered a good conductor because it has
many free electrons.  Electrical energy is transferred through conductors by
means of the movement of free electrons that migrate from atom to atom inside
the conductor.  Each electron moves a very short distance to the neighboring
atom where it replaces one or more electrons by forcing them out of their
orbits.  The replaced electrons repeat the process in other nearby atoms until
the movement is transmitted throughout the entire length of the conductor.

Substances that permit the free motion of a large number of electrons are
called __________.
ANSWER CONDUCTORS





The greater the number of electrons that can be made to move in a material under
the application of a given force the better are the conductive qualities of that
material.  A good conductor is said to have a low opposition or low resistance
to the current (electron) flow.  Among the most commonly known metals used as
conductors are silver, copper, and aluminum.  The best conductors are silver,
copper, and aluminum, in that order.  However, copper is used more extensively
because it is less expensive.  A material's ability to conduct electricity also
depends on its dimensions.

A good conductor is said to have a low opposition or low __________ to the
current (electron) flow.
ANSWER RESISTANCE





    In contrast to good conductors, some substances such as rubber, glass, and
dry wood have very few free electrons.  In these materials large amounts of
energy must be expended in order to break the electrons loose from the influence
of the nucleus.  Substances containing very few free electrons are called POOR
CONDUCTORS, NONCONDUCTORS, or INSULATORS.  Actually, there is no sharp dividing
line between conductors and insulators, since electron motion is known to exist
to some extent in all matter.  Electricians simply use the best conductors as
wires to carry current and the poorest conductors as insulators to prevent the
current from being diverted from the wires.

Poor conductors are called __________.
ANSWER INSULATORS




    Listed below are some of the best conductors and best insulators arranged in
accordance with their respective abilities to conduct or to resist the flow of
electrons.
                            Conductors     Insulators
                             Silver         Dry air
                             Copper         Glass
                             Aluminum       Mica
                             Zinc           Rubber
                             Brass          Asbestos
                             Iron           Bakelite

Glass is considered a(an) _________.
ANSWER INSULATOR







    A semiconductor is a material that is neither a good conductor nor a good
insulator.  Germanium and silicon are substances that fall into this category.
These materials, due to their peculiar crystalline structure, may under certain
conditions act as conductors; under other conditions, as insulators.  As the
temperature is raised, however, a limited number of electrons become available
for conduction.

A _____________ is a material that is neither a good conductor nor a good
insulator.
ANSWER SEMICONDUCTOR
                               STATIC ELECTRICITY
    In a natural, or neutral state, each atom in a body of matter will have the
proper number of electrons in orbit around it.  Consequently, the whole body of
matter comprised of the neutral atoms will also be electrically neutral.  In
this state, it is said to have a "zero charge," and will neither attract nor
repel other matter in its vicinity.  Electrons will neither leave nor enter the
neutrally charged body should it come in contact with other neutral bodies.  If,
however, any number of electrons are removed from the atoms of a body of matter,
there will remain more protons than electrons, and the whole body of matter will
become electrically positive.  Should the positively charged body come in
contact with another body having a normal charge, or having a negative (too many
electrons) charge, an electric current will flow between them.  Electrons will
leave the more negative body and enter the positive body.  This electron flow
will continue until both bodies have equal charges.

Electrons flow from more ____________ body to the more positive body.
ANSWER NEGATIVE






    When two bodies of matter have unequal charges, and are near one another, an
electric force is exerted between them because of their unequal charges.
However, since they are not in contact, their charges cannot equalize.  The
existence of such an electric force, where current cannot flow, is referred to
as static electricity.  "Static" means "not moving."   This is also referred to
as an ELECTROSTATIC FORCE.

The existence of an electric force produced by two unequal charges, where
current cannot flow, is referred to as ______ electricity.

ANSWER STATIC






    One of the easiest ways to create a static charge is by the friction method.
With the friction method, two pieces of matter are rubbed together and electrons
are "wiped off" one onto the other.  If materials that are good conductors are
used, it is quite difficult to obtain a detectable charge on either.  The reason
for this is that equalizing currents will flow easily in and between the
conducting materials.  These currents equalize the charges almost as fast as
they are created.

One of the easiest ways to create static electricity is by ________.
ANSWER FRICTION






    A static charge is easier to obtain by rubbing a hard nonconducting material
against a soft, or fluffy, nonconductor.  Electrons are rubbed off one material
and onto the other material.  This is illustrated in figure 4.
    When the hard rubber rod is rubbed in the fur, the rod accumulates
electrons.  Since both fur and rubber are poor conductors, little equalizing
current can flow, and an electrostatic charge is built up.  When the charge is
great enough, equalizing currents will flow regardless of the material's poor
conductivity.  These currents will cause visible sparks, if viewed in darkness,
and produce a cracking sound.

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                                 CHARGED BODIES

    One of the fundamental laws of electricity is that LIKE CHARGES REPEL EACH
OTHER and UNLIKE CHARGES ATTRACT each OTHER.  A positive charge and negative
charge, being unlike, tend to move toward each other.  In the atom the negative
electrons are drawn toward the positive protons in the nucleus.  This attractive
force is balanced by the electron's centrifugal force caused by its rotation
about the nucleus.  As a result, the electrons remain in orbit and are not drawn
into the nucleus.  Electrons repel each other because of their like negative
charges, and protons repel each other because of their like positive charges.

Like charges _____ each other.
ANSWER REPEL

    The law of charged bodies may be demonstrated by a simple experiment.   Two
pith (paper pulp) balls are suspended near one another by threads, as shown in
figure 5.
    If the hard rubber rod is rubbed to give it a negative charge, and then held
against the right hand ball in part (A), the rod will impart a negative charge
to the ball.  The right-hand ball will be charged negative with respect to the
left hand ball.  When released, the two balls will be drawn together, as shown
in figure 5 (A), they will touch and remain in contact until the left hand ball
acquires a portion of the negative charge of the right-hand ball, at which time
they will swing apart as shown in figure 5 (C).  If, positive charges are placed
on both balls (fig. 5 (B)), the balls will also be repelled from each other.



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                            COULOMB'S LAW OF CHARGES

    The amount of attracting or repelling force which acts between two
electrically charged bodies in free space depends on two things - (1) their
charges, and (2) the distance between them.  The relationship of charge and
distance to electrostatic force was first discovered and written by a French
scientist named Charles A. Coulomb.  Coulomb's Law states that CHARGED BODIES
ATTRACT OR REPEL EACH OTHER WITH A FORCE THAT IS DIRECTLY PROPORTIONAL TO THE
PRODUCT OF THEIR CHARGES, AND IS INVERSELY PROPORTIONAL TO THE SQUARE OF THE
DISTANCE BETWEEN THEM.

Charged bodies attract or repel each other with a force the is ________
proportional to their charges, and is inversely proportional to the square of
the distance between them.
ANSWER DIRECTLY



                                 ELECTRIC FIELDS

    The space between and around charged bodies in which their influence is felt
is called an ELECTRIC FIELD OF FORCE.  The electric field is always terminated
on material objects and extends between positive and negative charges.  It can
exist in air, glass, paper, or a vacuum. ELECTROSTATIC FIELDS and DIELECTRIC
FIELDS are other names used to refer to this region of force.
    Fields of force spread out in the space surrounding their point of origin
and, in general, DIMINISH IN PROPORTION TO THE SQUARE OF THE DISTANCE FROM THEIR
SOURCE.

The space between and around charged bodies in which their influence is felt
is called an ________ _____ of force.
ANSWER ELECTRIC FIELD




    The field about a charged body is generally represented by lines which are
referred to as ELECTROSTATIC LINES OF FORCE.  These lines are imaginary and are
used merely to represent the direction and strength of the field.  To avoid
confusion, the lines of force exerted by a positive charge are always shown
leaving the charge, and for a negative charge they are shown as entering.
Figure 6 illustrates the use of lines to represent the field about charged
bodies.
    Figure 6 (A) represents the repulsion of like-charged bodies and their
associated fields.  Part (B) represents the attraction between unlike-charged
bodies and their associated fields.

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                                    MAGNETISM

    A substance is said to be a magnet if it has the property of magnetism -
that is, if it has the power to attract such substances as iron, steel, nickel,
or cobalt, which are known as MAGNETIC MATERIALS.  A steel knitting needle,
magnetized by a method to be described later, exhibits two points of maximum
attraction (one at each end) and no attraction at its center.  The points of
maximum attraction are called MAGNETIC POLES.  All magnets have at least two
poles.  If the needle is suspended by its middle so that it rotates freely in a
horizontal plane about its center, the needle comes to rest in a approximately
north - south line of direction.  The same pole will always point to the north,
and the other will always point toward the south.  The magnetic pole that points
northward is called the NORTH POLE, and the other the SOUTH POLE.

The points of maximum attraction on a magnet are called the ________ _____.
ANSWER MAGNETIC POLES




    A MAGNETIC FIELD exists around a simple bar magnet.  The field consists of
imaginary lines along which a MAGNETIC FORCE acts.  These lines emanate from the
north pole of the magnet, and enter the south pole, returning to the north pole
through the magnet itself, thus forming closed loops.
    A MAGNETIC CIRCUIT is a complete path through which magnetic lines of force
may be established under the influence of a magnetizing force.  Most magnetic
circuits are composed largely of magnetic materials in order to contain the
magnetic flux.  These circuits are similar to the ELECTRIC CIRCUIT, which is a
complete path through which current is caused to flow under the influence of an
electromotive force.

A ________ circuit is similar to an electric circuit.
ANSWER MAGNETIC




     Magnets may be conveniently divided into three groups.

     1. NATURAL MAGNETS, found in the natural state in the form of a mineral
        called magnetite.
     2. PERMANENT MAGNETS, bars of hardened steel (or some form of alloy such as
        alnicol that have been permanently magnetized.
     3. ELECTROMAGNETS, composed of soft iron cores around which are wound coils
        of insulated wire.  When an electric current flows through the coil, the
        core becomes magnetized.  When the current ceases to flow, the core
        loses most of its magnetism.

Natural magnets are formed of a mineral called ________.
ANSWER MAGNETITE











    Permanent magnets and electromagnets are sometimes called ARTIFICIAL MAGNETS
to further distinguish them from natural magnets, and are discussed in grater
detail in other lessons.

Magnets that are not natural magnets are called _________ magnets.
ANSWER ARTIFICIAL
                                 NATURAL MAGNETS

    For many centuries it has been known that certain stones (magnetite, Fe3O4)
have the ability to attract small pieces of iron.  Because many of the best of
these stones (natural magnets) were found near Magnesia in Asia Minor, the
Greeks called the substance MAGNETITE, or MAGNETIC.
    Before this, ancient Chinese observed that when similar stones were
suspended freely, or floated on a light substance in a container of water, they
tended to assume a nearly north - and south position.  Probably Chinese
navigators used bits of magnetite floating on wood in a liquid filled vessel as
crude compasses.  At that time it was not known that the earth itself acts like
a magnet, and these stones were regarded with considerable superstitious awe.
Because bits of this substance were used as compasses they were called
LOADSTONES (or lodestones), which means "leading stones."

Bits of magnet may be used as crude compasses, and are called __________.
ANSWER LOADSTONES

Natural magnets are also found in the United States, Norway, and Sweden.  A
natural force at the poles, is shown in figure 7 (A).


                               ARTIFICIAL MAGNETS

    Natural magnets no longer have any practical value because more powerful and
more conveniently shaped permanent magnets can be produced artificially.
Commercial magnets are made from special steels and alloys - for example,
alnico, made principally of aluminum, nickel, and cobalt.  The name is derived
from the first two letters of the three principal elements of which it is
composed.  An artificial magnet is shown in figure 7 (B).

The artificial magnet material that is made from a combination of aluminum,
nickel, and cobalt is called ______.
ANSWER ALNICO






    An iron, steel, or alloy bar can be magnetized by inserting the bar into a
coil of insulated wire and passing a heavy direct current through the coil, as
shown in figure 8 (A).  This aspect of magnetism is treated later.  The same bar
may also be magnetized if it is stroked with a bar magnet, as shown in
figure 8 (B).  It will then have the same magnetic property that the magnet used
to induce the magnetism has namely, there will be two poles of attraction, one
at either end.  This process produces a permanent magnet by INDUCTION - that is,
the magnetism is induced by the influence of the stroking magnet.

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    Artificial magnets maybe classified as "permanent" or "temporary" depending
on their ability to retain their magnetic strength after the magnetizing force
has been removed.  Hardened steel and certain alloys are relatively difficult to
magnetize and are said to have a LOW PERMEABILITY because the magnetic lines of
force do not easily permeate, or distribute themselves readily through the
steel. (Permeability is a measure of the relative ability of a substance to
conduct magnetic lines of force as compared with air.  It is discussed in
greater detail in another lesson.)  Once magnetized, however, these materials
retain a large part of their magnetic strength and are called PERMANENT MAGNETS.
Permanent magnets are used extensively in electric instruments, meters,
telephone receivers, permanent-magnet (PM) loudspeakers, and magnetos.


The measure of the relative ability of a substance to conduct magnetic lines of
force as compared with air is called ____________.
ANSWER PERMEABILITY


    Conversely, substances that are relatively easy to magnetize -- such as soft
iron and annealed silicon steel -- are said to have HIGH PERMEABILITY.  Such
substances retain only a small part of their magnetism after the magnetizing
force is removed and are called TEMPORARY MAGNETS.  Silicon steel and similar
materials are used in transformers where the magnetism is constantly changing
and in generators and motors where the strength of the fields can be readily
changed.)
    The magnetism that remains in a temporary magnet after the magnetizing force
is removed is called RESIDUAL MAGNETISM.  The fact that temporary magnets retain
even a small amount of magnetism is an important factor in the buildup of
voltage in self-excited d-c generators.

Temporary magnets are used in ____________ where the magnetism is constantly
changing.
ANSWER TRANSFORMERS


                              NATURE OF  MAGNETISM

    A popular theory of magnetism considers the molecular alignment of the
material. This is known as Weber's Theory.  This theory assumes all magnetic
substances to be composed of tiny molecular magnets.  All unmagnetized materials
have the magnetic forces of its molecular magnets neutralized by adjacent
molecular magnets thereby eliminating any magnetic effect.  A magnetized
material will have most of its molecular magnets lined up so that the north pole
of each molecule points in one direction, and the south pole faces the opposite
direction.  A material with its molecules thus aligned will then have one
effective north pole, and one effective south pole.

The theory of magnetism that assumes molecular alignment is known as _______
theory.
ANSWER WEBER'S








An illustration of Weber's Theory is shown in figure 9 (A) where a steel bar is
magnetized by stroking.  When a steel bar is stroked several times in the same
direction by a magnet, the magnetic force from the north pole of the magnet
causes the molecules to align themselves.  The polarity of the magnet formed is
dependent upon the direction of the magnetizing force as it is brought over the
random magnetic molecules.

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    Some justification of Weber's Theory occurs when a magnet is split in half.
It is found that each half possess both a north and a south magnetic pole as
shown in figure 9 (B).  The polarities of the poles are in the same respective
directions as the poles of the original magnet.  If a magnet is further divided
into small parts, it will be found that each part, down to its last molecule,
will all have similar north and south poles.  Each part would exhibit its own
magnetic properties.

When a magnet is cut in half each half possess both a north and a south ____.
ANSWER POLE







    Further support of Weber's theory comes from the fact that when a bar magnet
is held out of alignment with the earth's magnetic field and repeatedly jarred
or heated, the molecular alignment is disarranged and the material becomes
demagnetized.  For example, measuring devices which make use of permanent
magnets become inaccurate when subjected to severe jarring or exposure to
opposing magnetic fields.

If a bar magnet is severely jarred or exposed to opposing magnetic fields it may
become ____________.
ANSWER DEMAGNETIZED



                                  DOMAIN THEORY

    A more modern theory of magnetism is based on the electron spin principle.
From the study of atomic structure it is known that all matter is composed of
vast quantities of atoms, each atom containing one or more orbital electrons.
The electrons are considered to orbit in various shells and subshells depending
upon their distance from the nucleus.  The structure of the atom has previously
been compared to the solar system, wherein the electrons orbiting the nucleus
correspond to the planets orbiting the sun.  Along with their orbital motion
about the sun, these planets also revolve on their axes.   It is believed that
the electron also revolves on its axis as it orbits the nucleus of an atom.

A more modern theory of magnetism is based on the electron ____ principle.
ANSWER SPIN


    It has been experimentally proven that an electron has a magnetic field
about it along with an electric field. The effectiveness of the magnetic field
of an atom is determined by the number of electrons spinning in each direction.
If an atom has equal numbers of electrons spinning in opposite directions, the
magnetic fields surrounding the electrons cancel one another, and the atom is
unmagnetized.  However, if more electrons spin in one direction than another,
the atom is magnetized.  An atom such as iron with an atomic number of 26 has 26
protons in the nucleus and 26 revolving electrons orbiting its nucleus.  If 13
electrons are spinning in a clockwise direction and 13 electrons are spinning in
a counterclockwise direction, the opposing magnetic fields will be neutralized.
When more than 13 electrons spin in either direction, the atom is magnetized.

When more electrons spin in one direction than the other the atom is thought to
be __________.
ANSWER MAGNETIZED








An example of a magnetized atom of iron is shown in figure 10.  Note that in
this specific illustration the electrons magnetic fields in all except the M
shell neutralize each other.  As illustrated in the diagram, there exists 15
electrons spinning in one direction and only 11 electrons spinning in an
opposite direction.  Therefore, the unopposed magnetic fields of 4 electrons
will cause this iron atom to become an infinitely small magnet.

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    When a number of such atoms are grouped together to form an iron bar, there
is an interaction between the magnetic forces of various atoms.  The small
magnetic force of the field surrounding an atom affects adjacent atoms, thus
producing a small group of atoms with parallel magnetic fields.  This group of
magnetic atoms is known as a DOMAIN.  Throughout a domain there is an intense
magnetic field without the influence of any external magnetic field.  Since
about 10 million tiny domains can be contained in 1 cubic millimeter, it is
apparent that every magnetic material is made up of a large number of domains.
The domains in any substance are always magnetized but are randomly orientated
throughout a material.  Thus, the strong magnetic field of each domain is
neutralized by opposing magnetic forces of other domains.  When an external
field is applied to a magnetic substance the domains will line up with the
external field.  The magnetic strength of a magnetized material is determined by
the number of domains aligned by the magnetizing force.

A number of atoms with similar magnetic poles group together to form a ______.
ANSWER DOMAIN





                       MAGNETIC FIELDS AND LINES OF FORCE

    If a bar magnet is dipped into iron filings, many of the filings are
attracted to the ends of the magnet, but none are attracted to the center of the
magnet.  As mentioned previously, the ends of the magnet where the attractive
force is the greatest are called the POLES of the magnet.  By using a compass,
the line of direction of the magnetic force at various points near the magnet
may be observed.  The compass needle itself is a magnet.

If a bar magnet is dipped into iron filings, many of the filings are attracted
to the _____ of the magnet.
ANSWER ENDS









The north end of the compass needle always points toward the south pole, S, as
shown in figure 11 (A), and thus the sense of direction (with respect to the
polarity of the bar magnet) is also indicated.  At the center, the compass
needle points in a direction that is parallel to the bar magnet.

The ______ end of a compass needle always points toward the south pole of
another magnet.
ANSWER NORTH
    When the compass is placed successively at several points in the vicinity of
the bar magnet the compass needle aligns itself with the field at each position.
The direction of the field is indicated by the arrows and represents the
direction in which the north pole of the compass needle will point when the
compass is placed in this field.  Such a line along which a compass needle
aligns itself is called a MAGNETIC LINE OF FORCE.  This magnetic line of force
does not actually exist but is an imaginary line used to illustrate and describe
the pattern of the magnetic field.  As mentioned previously, the magnetic
lines of force are assumed to emanate from the north pole of a magnet, pass
through the surrounding space, and enter the south pole.  The lines of force
then pass from the south pole to the north pole inside the magnet to form a
closed loop.  Each line of force forms an independent closed loop and does not
merge with or cross other lines of force.

The _______ lines of force pass from the south to the north pole of the magnet
through the center of the magnet.
ANSWER MAGNETIC






The lines of force between the poles of a horseshoe magnet are shown in
figure 11 (B).

    Although magnetic lines of force are imaginary, a simplified version of many
magnetic phenomena can be explained by assuming the magnetic lines to have
certain real properties.  The lines of force can be compared to rubber bands
which stretch outward when a force is exerted upon them and contract when the
force is removed.

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The characteristics of magnetic lines of force can be described as follows:
     1. Magnetic lines of force are continuous and will always form closed
        loops.
     2. Magnetic lines of force will never cross one another.
     3. Parallel magnetic lines of force traveling in the same direction repel
        one another.  Parallel magnetic lines of force traveling in opposite
        directions tend to unite with each other and form into single lines
        traveling in a direction determined by the magnetic poles creating the
        lines of force.
     4. Magnetic lines of force tend to shorten themselves.  Therefore, the
        magnetic lines of force existing between two unlike poles cause the
        poles to be pulled together.
     5. magnetic lines of force pass through all materials, both magnetic and
        nonmagnetic.

Magnetic lines of force pass through all materials, both magnetic and _________.
ANSWER NONMAGNETIC
    The space surrounding a magnet, in which the magnetic force acts, is called
a MAGNETIC FIELD.  Michael Faraday was the first scientist to visualize the
magnet field as being in a state of stress and consisting of uniformly
distributed lines of force.  The entire quantity of magnetic lines surrounding a
magnet is called MAGNETIC FLUX.  Flux in a magnetic circuit corresponds to
current in an electric circuit.
    The number of lines of force per unit area is called FLUX DENSITY and is
measured in lines per square inch or lines per square centimeter.  Flux density
is expressed by the equation where B is the flux density,  (Greek phi) is the
total number of lines of flux, and A is the crosssectional area of the magnetic
circuit.  If A is in square centimeters, B is in lines per square centimeter, or
GAUSS.  The terms FLUX and FLOW of magnetism are frequently used in textbooks.
However, magnetism itself is not thought to be a stream of particles in motion,
but is simply a field of force exerted in space.

The space surrounding a magnet is called a ________ _____ .
ANSWER MAGNETIC FIELD





    A visual representation of the magnetic field around a magnet can be
obtained by placing a plate of glass over a magnet and sprinkling iron filings
onto the glass.  The filings arrange themselves in definite paths between the
poles.  This arrangement of the filings shows the pattern of the magnetic field
around the magnet, as in figure 12.  The magnetic field surrounding a
symmetrically shaped magnet has the following properties:
     1. The field is symmetrical unless disturbed by another magnetic substance.
     2. The lines of force have direction and are represented as emanating from
        the north pole and entering the south pole.

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                        LAWS OF ATTRACTION AND REPULSION

    If a magnetized needle is suspended near a bar magnet, as in figure 13, it
will be seen that a north pole repels a north pole and a south pole repels a
south pole.  Opposite poles, however, will attract each other.  Thus, the first
two laws of magnetic attraction and repulsion are:
     1. LIKE magnetic poles REPEL each other.
     2. UNLIKE magnetic poles ATTRACT each other.


Like magnetic poles _____ each other.
ANSWER REPEL










    The flux patterns between adjacent UNLIKE poles of bar magnets, as indicated
by lines, are shown in figure 14 (A).  Similar patterns for adjacent LIKE poles
are shown in figure 14 (B).  The lines do not cross at any point and they act as
if they repel each other.

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    Figure 15 shows the flux pattern (indicated by lines) around two bar magnets
placed close together and parallel with each other.  Figure 15 (A) shows the
flux pattern when opposite poles are adjacent; and figure 15 (B) shows the flux
pattern when like poles are adjacent.

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    The THIRD LAW of magnetic attraction and repulsion states in effect that the
force of attraction or repulsion existing between two magnetic poles decreases
rapidly as the poles are separated from each other.  Actually, the force of
attraction or repulsion varies directly as the product of the separate pole
strengths and inversely as the square of the distance separating the magnetic
poles, provided the poles are small enough to be considered as points.  For
example, if the distance between two north poles is increased from 2 feet to 4
feet, the force of repulsion between them is decreased to one-fourth of its
original value.  If either pole strength is doubled, the distance remaining the
same, the force between the poles will be doubled.

The THIRD LAW of magnetic attraction and repulsion states in effect that the
force of attraction or repulsion existing between two magnetic poles _________
_______ as the poles are separated from each other.
ANSWER DECREASES RAPIDLY
                              THE EARTH'S MAGNETISM

    As has been stated, the earth is a huge magnet; and surrounding the earth is
the magnetic field produced by the earth's magnetism.  The magnetic polarities
of the earth are as indicated in figure 16.  The geographic poles are also shown
at each end of the axis of rotation of the earth.  The magnetic axis does not
coincide with the geographic axis, and therefore the magnetic and geographic
poles are not at the same place on the surface of the earth.
    The early users of the compass regarded the end of the compass needle that
points in a northerly direction as being a north pole.  The other end was
regarded as a south pole.  On some maps the magnetic pole of the earth towards
which the north pole of the compass pointed was designated  a north magnetic
pole.  This magnetic pole was obviously called a north pole because of its
proximity to the north geographic pole.

As has been stated, the earth is a ____ ______.
ANSWER HUGE MAGNET


    When it was learned that the earth is a magnet and that opposite poles
attract, it was necessary to call the magnetic pole located in the northern
hemisphere a SOUTH MAGNETIC POLE and the magnetic pole located in the southern
hemisphere a NORTH MAGNETIC POLE.  The matter of naming the poles was arbitrary.
Therefore, the polarity of the compass needle that points toward the north must
be opposite to the polarity of the earth's magnetic pole located there.
    Because the magnetic poles and the geographic poles do not coincide, a
compass will not (except at certain positions on the earth) point in a true
(geographic) north-south direction - that is, it will not point in a line of
direction that passes through the north and south geographic poles, but in a
line of direction that makes an angle with it.  This angle is called the angle
of VARIATION OR DECLINATION.

The angle that a compass is off is called the angle of variation or ___________.
ANSWER DECLINATION


                               MAGNETIC SHIELDING

    There is not a known INSULATOR for magnetic flux.  If a nonmagnetic material
is placed in a magnetic field, there is no appreciable change in flux - that is,
the flux penetrates the nonmagnetic material.  For example, a glass plate placed
between the poles of a horseshoe magnet will have no appreciable effect on the
field although glass itself is a good insulator in an electric circuit.  If a
magnetic material (for example, soft iron) is placed in a magnetic field, the
flux may be redirected to take advantage of the greater permeability of the
magnetic material as shown in figure 17.  Permeability, as discussed earlier, is
the quality of a substance which determines the ease with which it can be
magnetized.

Is there a good insulator for magnetic flux? (YES/NO)
ANSWER NO





    The sensitive mechanism of electric instruments and meters can be influenced
by stray magnetic fields which will cause errors in their readings.  Because
instrument mechanisms cannot be insulated against magnetic flux, it is necessary
to employ some means of directing the flux around the instrument.  This is
accomplished by placing a soft-iron case, called a MAGNETIC SCREEN OR SHIELD,
about the instrument.  Because the flux is established more readily through the
iron (even though the path is longer) than through the air inside the case, the
instrument is effectively shielded, as shown by the watch and soft-iron shield
in figure 18.

The best shield for magnetic flux is soft-____.
ANSWER IRON

                               MAGNETIC MATERIALS

    Early magnetic studies classified materials merely as being magnetic and
nonmagnetic.  Present studies classify materials into one of three groups;
namely, paramagnetic, diamagnetic, and ferromagnetic.
    PARAMAGNETIC materials are those that become only slightly magnetized even
though under the influence of a strong magnetic field.  This slight
magnetization is in the same direction as the magnetizing field.  Materials of
this type are aluminum, chromium, platinum, and air.
    DIAMAGNETIC materials can also be only slightly magnetized when under the
influence of a very strong field.  These materials, when slightly magnetized,
are magnetized in a direction opposite to the external field.  Some diamagnetic
materials are copper, silver, gold, and mercury.

Silver is considered a ___________ material.
ANSWER DIAMAGNETIC

    Paramagnetic and diamagnetic materials have a very low permeability.
Paramagnetic materials have a permeability slightly greater than one;
diamagnetic materials have a permeability less than one.  Because of the
difficulty in obtaining some magnetization of paramagnetic and diamagnetic
materials, these materials are considered for all practical purposes as
nonmagnetic materials.
    The most important group of materials for applications of electricity and
electronics are the FERROMAGNETIC MATERIALS.  Ferromagnetic materials are those
which are relatively easy to magnetize such as iron, steel, cobalt, Alnico, and
Permalloy, the latter two being alloys.  Alnico consists primarily of aluminum,
nickel, and cobalt.  These new alloys can be very strongly magnetized with
Alnico capable of obtaining a magnetic strength great enough to lift five
hundred times its own weight.

Paramagnetic and diamagnetic materials have a very low ____________.
ANSWER PERMEABILITY
    Ferromagnetic materials all have a high permeability. However, as previously
discussed, a material, such as steel used to make a permanent magnet, is
considered to have a relatively low permeability in comparison to other
ferromagnetic materials.

                                 MAGNETIC SHAPES

    Because of the many uses of magnets, they are found in various shapes and
sizes.  However, magnets usually come under three general classifications;
namely, bar magnets, horseshoe magnets, and ring magnets.
    The bar magnet is most often used in schools and laboratories for studying
the properties and effects of magnetism.  In the preceding test material, the
bar magnet proved very helpful in demonstrating magnetic effects.

The ___ ______ is most often used in schools and laboratory for studying the
properties and effects of magnetism.
ANSWER BAR MAGNET


    Another type of magnet is the ring magnet used for computer memory cores.  A
common application for a temporary ring magnet would be the shielding of
electrical instruments as previously discussed.
    The shape of the magnet most frequently used in electrical or electronic
equipment is called the horseshoe magnet.  A horseshoe magnet is similar to a
bar magnet but is bent in the shape of a horseshoe.  The horseshoe magnet
provides much more magnetic strength than a bar magnet of the same size and
material because of the closeness of the magnetic poles.  The magnetic strength
from one pole to the other is greatly increased due to the concentration of the
magnetic field in a smaller area. Electrical measuring devices quite frequently
use horseshoe type magnets.

The shape of the magnet most frequently used in electrical or electronics
equipment is called the _________ ______.
ANSWER HORSESHOE MAGNET





                                 CARE OF MAGNETS

    A piece of steel that has been magnetized can lose much of its magnetism by
improper handling.  If it is jarred or heated, there will be a disalignment of
its domains resulting in the loss of some of its effective magnetism.  Had this
steel formed the horseshoe magnet of a meter, the meter would no longer be
operable or would give inaccurate readings.  Therefore, care must be exercised
when handling instruments containing magnets. Severe jarring or subjecting the
instrument to high temperature will damage the device.

Severe jarring may ______ a device that contains a magnet.
ANSWER DAMAGE




    A magnet may also become weakened from loss of flux.  Thus, when storing
magnets one should always try to avoid excess leakage of magnetic flux.  A
horseshoe magnet should always be stored with a keeper, a soft iron bar used to
join the magnetic poles.  By use of the keeper while the magnet is being stored,
the magnetic flux will continuously circulate through the magnet and not leak
off into space.
    When storing bar magnets, the same principle must be remembered.  Therefore,
bar magnets should always be stored in pairs with a north pole and a south pole
placed together.  This provides a complete path for the magnetic flux without
any flux leakage.

A magnet may become ________ from the loss of flux.
ANSWER WEAKENED







    The study of electricity and magnetism and how they interact with each other
is given more thorough coverage in later lessons. The discussion of magnetism up
to this point has been mainly intended to clarify terms and meanings, such as
"polarity," "fields," "lines of force," etc.  Only one fundamental relationship
between magnetism and electricity is discussed in this lesson.  This
relationship pertains to magnetism as used to generate a voltage and it is
discussed in the material that follows.

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                            DIFFERENCE IN POTENTIAL

    The force that causes free electrons to move in a conductor as an electric
current may be referred to as follows:

    1. Electromotive force (emf).
    2. Voltage.
    3. Difference in potential.

    When a difference in potential exists between two charged bodies that are
connected by a conductor, electrons will flow along the conductor.  This flow is
from the negatively charged body to the positively charged body until the two
charges are equalized and the potential difference no longer exists.

The force that causes free electrons to move in a conductor is called emf,
 _______, or difference in potential.
ANSWER VOLTAGE







    An analogy of this action is shown in the two water tanks connected by a
pipe and valve in figure 19.  At first the valve is closed and all the water
is in tank A.   Thus, the water pressure across the valve is at maximum.  When
the valve is opened, the water flows through the pipe from A to B until the
water level becomes the same in both tanks.  The water then stops flowing in the
pipe, because there is no longer a difference in water pressure between the two
tanks.

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    Current flow "through an electric circuit is directly proportional to the
difference in potential across the circuit, just as the flow of water through
the pipe in the previous figure is directly proportional to the difference in
water level in the two tanks.
    A fundamental law of current electricity is that the CURRENT IS DIRECTLY
PROPORTIONAL TO THE APPLIED VOLTAGE; that is, if the voltage is increased, the
current is increased.  If the voltage is decreased, the current is decreased.

Current is ________ proportional to the applied voltage.
ANSWER DIRECTLY

                     PRIMARY METHODS OF PRODUCING A VOLTAGE

    Presently, there are six commonly used methods of producing electromotive
force (emf).  Some of these methods are much more widely used than others.  The
following is a list of the six most common methods of producing electromotive
force.

    1. FRICTION. - Voltage produced by rubbing two materials together.
    2. PRESSURE (Piezoelectricity). - Voltage produced by squeezing crystals of
       certain substances.
    3. HEAT (Thermoelectricity). - Voltage produced by heating the joint
       (junction) where two unlike metals are joined.

Voltage produced by heating the joint of two unlike metals is called
 _________________.
ANSWER THERMOELECTRICITY





    4. LIGHT (Photoelectricity). - Voltage produced by light striking
       photosensitive (light sensitive) substances.
    5. CHEMICAL ACTION. - Voltage produced by chemical reaction in a battery
       cell.
    6. MAGNETISM (Induction). - Voltage produced in a conductor when the
       conductor moves through a magnetic field, or a magnetic field moves
       through the conductor in such a manner as to cut the magnetic lines of
       force of the field.

Voltage produced by a conductor moving through an magnetic field is called
 _________.
ANSWER INDUCTION


                          VOLTAGE PRODUCED BY FRICTION

    This is the least used of the six methods of producing voltages.  Its main
application is in Van de Graf generators, used by some laboratories to produce
high voltages. As a rule, friction electricity (often referred to as static
electricity) is a nuisance.  For instance, a flying aircraft accumulates
electric charges from the friction between its skin and the passing air. These
charges often interfere with radio communication, and under some circumstances
can even cause physical damage to the aircraft.  Most individuals are familiar
with static electricity and have probably received unpleasant shocks from
friction electricity upon sliding across dry seat covers or walking across dry
carpets, and then coming in contact with some other object.

Static electricity is often a ________.
ANSWER NUISANCE






                          VOLTAGE PRODUCED BY PRESSURE

    This action is referred to as piezoelectricity. It is produced by
compressing or decompressing crystals of certain substances,  To study this form
of electricity, the meaning of the word "crystal" must first be understood.  In
a crystal, the molecules are arranged in an orderly and uniform manner.  A
substance in its crystallized state and its noncrystallized state is shown in
figure 20.

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    For the sake of simplicity, assume that the molecules of this particular
substance are spherical (ball-shaped).  In the noncrystallized state, in (A),
note that the molecules are arranged irregularly.  In the crystallized state,
(B), the molecules are arranged in a regular and uniform manner.  This
illustrates the major physical difference between crystal and noncrystal forms
of matter.  Natural crystalline matter is rare; an example of matter that is
crystalline in its natural form is diamond, which is crystalline carbon.  Most
crystals are manufactured.

In crystallized state molecules are arranged in a _______ and uniform manner.
ANSWER REGULAR

    Crystals of certain substances, such as Rochelle salt or quartz, exhibit
peculiar electrical characteristics.  These characteristics, or effects, are
referred to as "piezoelectric." For instance, when a crystal of quartz is
compressed, as in figure 20 (C), electrons tend to move through the crystal.
This tendency creates an electric difference of potential between the two
opposite faces of the crystal.  (The fundamental reasons for this action are not
known.  However, the action is predictable, and therefore useful.)  If an
external wire is connected while the pressure and emf are present, electrons
will flow.  If the pressure is held constant, the electron flow will continue
until the charges are equalized.  When the force is removed, the crystal is
decompressed, and immediately causes an electric force in the opposite
direction (D).  Thus, the crystal is able to convert mechanical force, either
pressure or tension, to electrical force.

A crystal is able to _______ mechanical force into electrical force.
ANSWER CONVERT










    The power capacity of a crystal is extremely small.  However, they are
useful because of their extreme sensitivity to changes of mechanical force or
changes in temperature.  Due to other characteristics not mentioned here,
crystals are most widely used in communication equipment.

The power capacity of a crystal is extremely _____.
ANSWER SMALL



                            VOLTAGE PRODUCED BY HEAT

    When a length of metal, such as copper, is heated at one end, electrons tend
to move away from the hot end toward the cooler end.  This is true of most
metals.  However, in some metals, such as iron, the opposite takes place and
electrons tend to move TOWARD the hot end.  These characteristics are
illustrated in figure 21.  The negative charges (electrons) are moving through
the copper away from the heat and through the iron toward the heat.  They cross
from the iron to the copper at the hot junction, and from the copper through the
current meter to the iron at the cold junction.  This device is generally
referred to as a thermocouple.

When iron is heated electrons move ______ the hot end.
ANSWER TOWARD






    Thermocouples have somewhat greater power capacities than crystals, but
their capacity is still very small if compared to some other sources.  The
thermoelectric voltage in a thermocouple depends mainly on the difference in
temperature between the hot and cold junctions.  Consequently, they are widely
used to measure temperature, and as heat-sensing devices in automatic
temperature control equipment.  Thermocouples generally can be subjected to much
greater temperatures than ordinary thermometers, such as the mercury or alcohol
types.

Thermocouples are widely used to measure ___________.
ANSWER TEMPERATURE


                            VOLTAGE PRODUCED BY LIGHT

    When light strikes the surface of a substance, it may dislodge electrons
from their orbits around the surface atoms of the substance.  This occurs
because light has energy, the same as any moving force.
    Some substances, mostly metallic ones, are far more sensitive to light than
others.  That is, more electrons will be dislodged and emitted from the surface
of a highly sensitive metal, with a given amount of light, than will be emitted
from a less sensitive substance.  Upon losing electrons, the photosensitive
(light sensitive) metal becomes positively charged, and an electric force is
created.  Voltage produced in this manner is referred to as (a photoelectric
voltage.)

When light strikes a photoelectric material it becomes _________ charged.
ANSWER POSITIVELY







    The photosensitive materials most commonly used to produce a photoelectric
voltage are various compounds of silver oxide or copper oxide.  A complete
device which operates on the photoelectric principle is referred to as a
"photoelectric cell." There are many sizes and types of photoelectric cells in
use, each of which serves the special purpose for which it was designed.  Nearly
all, however, have some of the basic features of the photoelectric cells shown
in figure 22.

A device that produces electricity from light is referred to as a ________ ____.
ANSWER PHOTOELECTRIC CELL





    The cell (fig. 22 (A)) has a curved light-sensitive surface focused on the
central anode.  When light from the direction shown strikes the sensitive
surface, it emits electrons toward the anode.  The more intense the light, the
greater is the number of electrons emitted.  When a wire is connected between
the filament and the back, or dark side, the accumulated electrons will flow to
the dark side.  These electrons will eventually pass through the metal of the
reflector and replace the electrons leaving the light-sensitive surface.  Thus,
light energy is converted to a flow of electrons, and a usable current is
developed.

In a photoelectric cell the electrons are collected on the _____.
ANSWER ANODE











    The cell (fig. 22 (B)) is constructed in layers.  A base plate of pure
copper is coated  with light-sensitive copper oxide.  An additional
semitransparent layer of metal is placed over the copper oxide.

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This additional layer serves two purposes:
    l. It is EXTREMELY thin to permit the penetration of light to the copper
       oxide.
    2. It also accumulates the electrons emitted by the copper oxide.
    An externally connected wire completes the electron path, the same as in the
reflector type cell.  The photocell's voltage is utilized as needed by
connecting the external wires to some other device, which amplifies (enlarges)
it to a usable level.
    A photocell's power capacity is very small.  However, it reacts to light
intensity variations in an extremely short time. This characteristic makes the
photocell very useful in detecting or accurately controlling a great number of
processes or operations.  For instance, the photoelectric cell, or some form of
the photoelectric principle, is used in television cameras, automatic
manufacturing process controls, door openers, burglar alarms, and so forth.

A television camera makes use of the _____________ principle.
ANSWER PHOTOELECTRIC

                       VOLTAGE PRODUCED BY CHEMICAL ACTION

    Up to this point, it has been shown that electrons may be removed from their
parent atoms and set in motion by energy derived from a source of friction,
pressure, heat, or light.  In general, these forms of energy do not alter the
molecules of the substances being acted upon.  That is, molecules are not
usually added, taken away, or split-up when subjected to these four forms of
energy.  Only electrons are involved.
    When the molecules of a substance are altered, the action is referred to as
CHEMICAL.  For instance, if the molecules of a substance combines with atoms of
another substance, or gives up atoms of its own, the action is chemical in
nature.  Such action always changes the chemical name and characteristics of the
substance affected.

When the molecules of a substance are altered, the action is referred to as:
ANSWER CHEMICAL






For instance, when atoms of oxygen from the air come 1st contact with bare iron,
they merge with the molecules of iron.  This iron is "oxidized." It has changed
chemically from iron to iron oxide, or "rust."  Its
molecules have been altered by chemical action.
    In some cases, when atoms are added to or taken away from the molecules of a
substance, the chemical change will cause the substance to take on an electric
charge.  The process of producing a voltage by chemical action is used in
batteries and is explained in a later lesson.

The process of producing a voltage by chemical action is used in ________.
ANSWER BATTERIES


                          VOLTAGE PRODUCED BY MAGNETISM

    Magnets or magnetic devices are used for thousands of different jobs.  One
of the most useful and widely employed applications of magnets is in the
production of vast quantities of electric power from mechanical sources.  The
mechanical power may be provided by a number of different sources, such as
gasoline or diesel engines, and water or steam turbines.  However, the final
conversion of these source energies to electricity is done by generators
employing the principle of electromagnetic induction.  These generators, of many
types and sizes, are discussed in later lessons.  The important subject to be
discussed here is the fundamental operating principle of ALL such
electromagnetic -induction generators.

A _________ uses magnetism to produce large quantities of electricity.
ANSWER GENERATOR
    To begin with, there are three fundamental conditions which must exist
before a voltage can be produced by magnetism.  They are as follows:
    1. There must be a CONDUCTOR, in which the voltage will be produced.
    2. There must be a MAGNETIC FIELD in the conductor's vicinity.
    3. There must be relative motion between the field and the conductor.  The
       conductor must be moved so as to cut across the magnetic lines of force,
       or the field must be moved so that the lines of force are cut by the
       conductor.

    In accordance with these conditions, when a conductor or conductors MOVE
ACROSS a magnetic field so as to cut the lines of force, electrons WITHIN THE
CONDUCTOR are impelled in one direction or another.  Thus, an electric force, or
voltage, is created.

There must be relative ______ between the field and inductor to produce
electricity using magnetism.
ANSWER MOTION







    In figure 23, note the presence of the three conditions needed for creating
an induced voltage:

    1. A magnetic field exists between the poles of the C-shaped magnet.
    2. There is a conductor (copper wire).
    3. There is relative motion.  The wire is moved back and forth ACROSS the
       magnetic field.

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    In figure 23 (A), the conductor is moving TOWARD the front of the page.
This occurs because of the magnetically induced emf acting on the electrons in
the copper.  The right-hand end becomes negative, and the left-hand end
positive.
    The conductor is stopped (B), motion is eliminated (one of the three
required conditions), and there is no longer an induced emf.  Consequently,
there is no longer any difference in potential between the two ends of the wire.
The conductor at (C) is moving away from the front of the page.  An induced emf
is again created.  However, note carefully that the REVERSAL OF MOTION has
caused a REVERSAL OF DIRECTION in the induced emf.

A reversal of motion causes a reversal of _________ in the induced emf.
ANSWER DIRECTION





    If a path for electron flow is provided between the ends of the conductor,
electrons will leave the negative end and flow to the positive end.  This
condition is shown in part (D).  Electron flow will continue as long as the emf
exists. In studying figure 23, it should be noted that the induced emf could
also have been created by holding the conductor stationary and moving the
magnetic field back and forth.
    The more complex aspects of power generation by use of mechanical motion and
magnetism are discussed in other lessons.

An induced emf may be created by holding a conductor stationary and moving the
________ _____ back and forth.
ANSWER MAGNETIC FIELD

                                ELECTRIC CURRENT

    The drift or flow of electrons through a conductor is called electric
current or electron flow.  During the early study of electricity, electric
current was erroneously assumed to be a movement of electrons from a positive
potential to a negative potential.  This assumption, termed conventional current
flow, is a concept that became entrenched in the minds of many scientists,
technicians, and writers.  Consequently, conventional current flow is indicated
in many textbooks, and this concept of electron movement should be realized.
However, since this early concept, it has been positively determined that the
direction of electron movement is from a region of negative potential to a
region of less negative potential or more positive potential.  Various terms may
be used in this manual and other textbooks to describe current flow.

The flow of electrons through a conductor is called electric _______.
ANSWER CURRENT






The terms current, current flow, electron flow, electron current, etc., may be
used to describe the same phenomenon; however, the reader should realize that
regardless of the term used, the movement of electrons will be from a negative
potential to a positive potential.
    Electric current is generally classified into two general types - direct
current and alternating current.  Direct current flows in the same direction
whereas an alternating current periodically reverses direction.  These two types
of current are discussed in greater detail later in other lessons.

In ______ current the electrons flow in the same direction all the time.
ANSWER DIRECT






    In order to determine the amount (number) of electrons flowing in a given
conductor, it is necessary to adopt a unit of measurement of current flow.   The
term AMPERE is used to define the unit of measurement of the rate at which
current flows (electron flow).  The symbol for current flow is I.  Current flow
is measured in amperes.  The abbreviation for ampere is amp.  One ampere may be
                                18
defined as the flow of 6.28 x 10   electrons per second past a fixed point in a
conductor.

The unit of current is called an ______.
ANSWER AMPERE




    A unit quantity of electricity is moved through an electric circuit when 1
ampere of current flows for 1 second of time.  This unit is equivalent to 6.28 x
  18
10   electrons, and is called the COULOMB.  The coulomb is to electricity as the
gallon is to water.  The symbol for the coulomb is Q" The rate of flow of
current in amperes and the quantity of electricity moved through a circuit are
related by the common factor of time.  Thus, the quantity of electric charge, in
coulombs, moved through a circuit is equal to the product of the current in
amperes, I, and the duration of flow in seconds, t.  Expressed as an equation,
Q = It.
         18
6.28 X 10   electrons are called a ______.
ANSWER COULOMB

    For example, if a current of 2 amperes flows through a circuit for 10
seconds the quantity of electricity moved through the circuit is 2 x 10, or 20
coulombs.  Conversely, current flow may be expressed in terms of coulombs and
time in seconds.  Thus, if 20 coulombs are moved through a circuit in 10
seconds, the average current flow is 20/10, or  2 amperes.  Note that the
current flow in amperes implies the rate of flow of coulombs per second without
indicating either coulombs or seconds.  Thus a current flow of 2 amperes is
equivalent to a rate of flow of 2 coulombs per second.  Frequently, the ampere
is much too large a unit for practical utilization.  Therefore, the milliampere
(ma), one-thousandth of an ampere (or the microampere, one-millionth of an
ampere), is used.  The device used to measure current is called an ammeter and
is discussed in a later lesson.

If 60 coulombs of electrons moves through a circuit in 4 seconds, what is the
amount of current?
ANSWER 15 AMPERES

                                   RESISTANCE

    Every material offers some resistance, or opposition, to the flow of
electric current through it.  Good conductors, such as copper, silver, and
aluminum, offer very little resistance. Poor conductors, or insulators, such as
glass, wood, and paper, offer a high resistance to current flow.
    The size and type of material of the wires in an electric circuit are chosen
so as to keep the electrical resistance as low as possible.  In this way,
current can flow easily through the conductors, just as water flows through the
pipe between the tanks in figure 19.  If the water pressure remains constant the
flow of water in the pipe will depend on how far the valve is opened.  The
smaller the opening, the greater the opposition to the flow, and the smaller
will be the rate of flow in gallons per second.

The opposition to current flow is called __________.
ANSWER RESISTANCE
    In the electric circuit, the larger the diameter of the wires, the lower
will be their electrical resistance (opposition) to the flow of current through
them.  In the water analogy, pipe friction opposes the flow of water between the
tanks.  This friction is similar to electrical resistance.  The resistance of
the pipe to the flow of water through it depends upon (l) the length of the
pipe, (2) the diameter of the pipe, and (3) the nature of the inside walls
(rough or smooth).   Similarly, the electrical resistance of the conductors
depends upon (1) the length of the wires, (2) the diameter of the wires, and (3)
the material of the wires (copper, aluminum, etc.).
    Temperature also affects the resistance of electrical conductors to some
extent. In most conductors (copper, aluminum, iron, etc.) the resistance
increases with temperature.  Carbon is an exception.  In carbon the resistance
decreases as temperature increases.  Certain alloys of metals (manganin and
constantan) have resistance that does not change appreciably with temperature.

The larger the wire, the _____ the resistance.
ANSWER LOWER




    The relative resistance of several conductors of the same length and cross
section is given in the following list with silver as a standard of 1 and the
remaining metals arranged in an order of ascending resistance:

         Silver. . .    .    .1.0
         Copper . .     .    .1.08
         Gold. . . .    .    .1.4
         Aluminum  .    .    .1.8
         Platinum .     .    .7.0
         Lead . . .     .    13.5

Which of the above materials is the best conductor?
ANSWER SILVER








    The resistance in an electrical circuit is expressed by the symbol R.
Manufactured circuit parts containing definite amounts of resistance are called
RESISTORS.  Resistance (R) is measured in OHMS.  One ohm is the resistance of a
circuit element, or circuit, that permits a steady current of 1 ampere (1
coulomb per second) to flow when a steady emf of 1 volt is applied to the
circuit.

Resistance is measured in _____.
ANSWER OHMS

                                   CONDUCTANCE

    Electricity is a study that is frequently explained in terms of opposites.
The term that is exactly the opposite of resistance is conductance.  Conductance
(G) is the ability of a material to pass electrons.  The unit of conductance is
the Mho, which is ohm spelled backwards.  Whereas the symbol used to represent
resistance is the Greek letter omega ( ), the symbol used to represent
conductance is the Greek letter omega upside down ( ).  The relationship that
exists between resistance and conductance is the reciprocal.  A reciprocal of a
number is obtained by dividing the number into one.  In terms of resistance and
conductance :

         R = 1/G        G = 1/R

The opposite of resistance is called ___________.
ANSWER CONDUCTANCE
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