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Generation of Electricity
1
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For
instance, if the molecules of a substance combine with atoms of another substance, or give
up atoms of its own, the action is chemical in nature
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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
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Typical examples are the primary cells (as used in electric torches), secondary cells (motor
car batteries), and fuel cells
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The most common use of this method of producing an
EMF is in the construction of a battery
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How It Works
The figure below shows the basic elements required to produce an EMF by chemical action
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A common electrolytic used in batteries is diluted sulphuric acid, but any number of
chemical compounds can be used
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The solution remains chemically stable until the
electrodes are introduced
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In this process the zinc electrode has gained the excess electrons that the sulphate
molecules gained from the combination with hydrogen
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These ions
travel to the copper electrode where they acquire electrons
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In giving up electrons, the copper electrode becomes positively charged
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The chemical action eventually ceases when the zinc electrode becomes so negative that it
repels the sulphate molecules and the positive charge on the copper electrode repels the
hydrogen ions
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Figure (39)

Distribution of charges in a cell
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The magnitude of this EMF is
typically 1
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Factors Effecting Chemical EMF Production

The magnitude of the EMF produced via chemical action can be affected by numerous
factors
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5 Volts
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For
example, in the event of an aircraft ditching into the sea, the placing of two electrodes into
the salt water can provide a small EMF that is capable of powering an emergency location
beacon
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Aircraft batteries are generally used for engine starts or auxiliary backup in emergency
situations
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While the principle itself was known for some time, this method of producing
electricity, due to its associated technological problems and high cost, was not considered
for practical purposes until recently, particularly in connection with space travel
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) into the fuel cell, where it will combine with an appropriate reducing agent (such as
hydrogen, petroleum gases, natural gas, alcohol, etc
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The electrodes and the
electrolyte enter into the process only to a limited extent and act mainly as catalysts
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Both the oxidiser and the fuel (reducing agent) can be fed into the cell, depending on its
type, either as gases or as liquids
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Fuel cells are extremely compact for
their output and very efficient
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Experimental work is
progressing towards overcoming technological and economical problems associated in an
endeavour to use these cells for the propulsion of vehicles, for portable power plants, etc
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MAGNETISM AND MOTION

There are three fundamental conditions which must exist before a voltage can be produced
by magnetism
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2
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3
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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
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Thus, an electric force, or voltage, is created
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A magnetic field exists between the poles of the C-shaped magnet
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The wire is moved back and forth
ACROSS the magnetic field
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This occurs because of the magnetically induced EMF acting on the electrons in
the copper
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Figure (40)
The three conditions for creating an induced EMF
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The conductor is stopped in Figure (41), motion is eliminated (one of the three required
conditions), and there is no longer an induced EMF
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The conductor at Figure (42) is
moving away from the front of the page
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However, note
carefully that the REVERSAL of MOTION has caused a REVERSAL of DIRECTION in the
induced EMF
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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
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Electron flow will continue as long as the EMF exists
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Figure (43)
Current flow when a conductor is connected
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Figure (44)
Tacho generator
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FRICTION
This is the least used of the methods of producing voltages
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As a rule, friction
electricity (often referred to as static electricity) is a nuisance
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4
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This occurs because light has energy, the same
as any moving force
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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
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Voltage produced in this manner is referred to as a
"photoelectric voltage"
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The cell in Figure (45) has a curved light sensitive surface focused on the central anode
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The more intense the light, the greater is the number of electrons emitted
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These electrons will eventually pass through the metal of the
reflector and replace the electrons leaving the light-sensitive surface
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Figure (46)
Layered solar cell construction
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A base plate of pure copper is coated with
light-sensitive copper oxide
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This additional layer serves two purposes:
1
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2
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An externally connected wire completes the electron path, the same as in the reflector type
cell
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A photocell's power capacity is very small
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This characteristic makes the photocell very useful in detecting
or accurately controlling a great number of processes or operations
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Figure (47)
Basic photovoltaic cell construction

A major step in the development of photovoltaic cells was made by the invention of the
solar cell, the main application of which is, as the name implies, to convert sunlight into
electricity
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When solar cells are connected in series and parallel into solar
batteries of suitable voltage and current output they are capable of sizeable, commercially
and industrially adequate outputs for operating electrical and electronic equipment and for
float-charging (usually nickel-cadmium) batteries to operate such equipment during cloudy
periods or during the night
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The positive base electrode is
made from a thin wafer, cut from the crystal grown from molten silicon, to which a minute
quantity of arsenic or similar material has been added during the growing stage, converting
it into an N-type or donor material which is eager to give up its surplus of electrons
A thin, transparent layer of P-type material is now applied to one side of the wafer
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Incident light
penetrating through the P-layer will enter the
N-layer and readily dislodge electrons there giving them the additional energy required to
pass through the boundary layer into the P-layer
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Typical loads consist of
radio relay stations, radio-telemetry and transmitting equipment, maritime lighthouses
and light buoys
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HEAT

In 1821, the German physicist Seebeck discovered that if he joined an iron wire in series
with two pieces of copper wire to form a closed circuit through a sensitive measuring
instrument and heated one of the copper-iron junctions, while the other remained at room
temperature, the needle of the instrument deflected due to a potential created in the
junction
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Figure (48)
Basic thermocouple
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Thus 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
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However, in some metals, such as iron the opposite takes place and electrons tend
to move TOWARD the hot end
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The negative charges (electrons) are moving through the copper away from the heat and
through the iron toward the heat
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Thermocouples generally can be subjected to much greater temperatures than ordinary
thermometers, such as the mercury or alcohol types
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PRESSURE
Voltage produced by pressure
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It is
produced by compressing or decompressing crystals of certain substances
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In a crystal, the molecules are arranged in an orderly and uniform manner
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Figure (49)
Molecules of a non-crystallized substance
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Note that the molecules are arranged irregularly in the non-crystallized state, in
Figure (49)
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In the crystallized state, Figure (50), the molecules are arranged in a regular and uniform
manner
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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)
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When the force is removed, the crystal is decompressed, and immediately causes an
electric force in the opposite direction Figure (52)
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Typical examples in the real world, of piezoelectric device applications are the common
everyday spark generator in lighters where the crystal is mechanically deformed by the
hammer mechanism and the resultant EMF is stepped up by transformer action to give the
high voltage spark
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An application of this conversion method in aircraft can be found in the form of vibration
measuring devices for monitoring engine operation (Early warning for bearing failure or
imbalance)
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