chapter 05 bennet
TRANSCRIPT
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Chapter 5
Fundamentals of Electricity
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Objectives (1 of 3)
Define the terms electricity and electronics.
Describe the atomic structure.
Outline how some of the chemical and
electrical properties of atoms are defined bythe number of electrons in their outer shells.
Outline the properties of conductors,
insulators, and semiconductors. Describe the characteristics of static
electricity.
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Objectives (2 of 3)
Define what is meant by the conventional andelectron theories of current flow.
Describe the characteristics of magnetism and the
relationship between electricity and magnetism.
Describe how electromagnetic field strength is
measured in common electromagnetic devices.
Define what is meant by an electrical circuit and the
terms voltage, resistance, and current flow.
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Objectives (3 of 3)
Outline the components required to constructa typical electrical circuit.
Perform electrical circuit calculations usingOhms law.
Identify the characteristics of DC and AC.
Describe some methods of generating acurrent flow in an electrical circuit.
Describe and apply Kirschhoffs first andsecond laws.
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Atomic Structure
and Electron Movement (1 of 7)
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Atomic Structure
and Electron Movement (2 of 7)
All matter is electrical in essence.
All matter is composed of atoms.
The atom is the smallest particle in a chemical
element.
The atomic structure of an element determines its
chemical and electrical characteristics.
The chemical and electrical properties of atoms aredefined by the number of electrons in their outer
shells.
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Atomic Structure
and Electron Movement (3 of 7) Nucleus
In the center of every atom is a nucleus.
Protons
The nucleus is made up of positively charged mattercalled protons.
Neutrons
The nucleus contains matter with no charge calledneutrons.
Electrons
Negatively charged particles called electrons areorbiting each atomic nucleus.
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Atomic Structure
and Electron Movement(4 of 7)
Electrons orbit the nucleus in concentric
paths called shells.
All electrons are alike -- AND -- all protonsare alike.
So where is the difference?
Every chemical element has a distinct identityand is made up of distinct atoms.
That is, each has a different number of
protons and electrons.
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Atomic Structure
and Electron Movement (5 of 7)
In an electrically balanced atom, the number of
protons equals the number of electrons.
This means that the atom is in what is described as a
neutral state of electrical charge. Ion
An atom with either a deficit or excess of electrons is
known as an ion.
Charge can move from one point to another.
Like charges repel.
Unlike charges attract.
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Atomic Structure
and Electron Movement (6 of 7)
Electrons (negative charge) are held in theirorbital shells by the nucleus (positive charge)of the atom.
Electrons are prevented from colliding witheach other because they all have similarnegative charges that tend to repel eachother.
A molecule is a chemically bonded union oftwo or more atoms.
A compound is a chemically bonded union ofatoms of two or more dissimilar elements.
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Atomic Structure
and Electron Movement (7 of 7)
All atoms have an electrical charge.
An atom is balanced when the number of protonsmatch the number of electrons and is said to be inan electrically neutral state.
Electricity is concerned with the behavior of atomsthat have become unbalanced or electrified.
Electricity may be defined as the movement of freeelectrons from one atom to another.
Current flow is a measurement of the number offree electrons passing a given point in an electricalcircuit per second.
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Conductors and Insulators (1 of 4)
Electron movementthrough a conductor is
referred to as current.
To produce current
flow, electrons mustmove from atom to
atom.
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Conductors and Insulators (3 of 4)
An insulator is anonmetallic substance
that contains five or
more electrons in its
outer shell or valence. Glass, mica, rubber,
and plastic are good
insulators.
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Conductors and Insulators (4 of 4)
Semiconductors are agroup of materials that
cannot be classified
either as conductors or
insulators. They have exactly four
electrons in their outer
shell.
Silicon (Si) is anexample of a
semiconductor.
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Current Flow (1 of 3)
Conventional theorystates that current
flows from positive to
negative.
Vehicle schematics useconventional theory
almost exclusively.
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Current Flow (2 of 3)
When the electron wasdiscovered, scientists
revised the theory of
current flow and called
it electron theory. The electron theory
states that current flow
is from negative to
positive.
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Current Flow (3 of 3)
Charge differential orvoltage is a measure of
electrical pressure. It is
referred to as:
Charge differential
Voltage (V)
Electro-motive force (EMF)
Potential difference (PD)
The greater the difference,
the greater will be the rate ofcurrent flow.
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Magnetism (1 of 3)
A bar shapedpermanent magnet has
a north and a south
pole at opposite ends.
Like poles repel. Unlike poles attract.
The lines of force
surrounding the
magnet are referred to
as flux lines.
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Magnetism (2 of 3)
Flux lines flow in one direction. Flux lines exit from the magnets north pole
and enter through the south pole.
The flux density (concentration) determinesthe magnetic force.
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Magnetism (3 of 3)
The flux density is always greatest at thepoles of a magnet.
Flux lines do not cross each other in a
permanent magnet. Flux lines facing the same direction attract.
Flux lines facing opposite directions repel.
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Electromagnetism (1 of 3)
Current flow throughany conductor createsa magnetic field.
Magnetic lines of force
do not change whenthe current flow througha conductor isconstant.
When current flow
increases, the lines offorce will extend furtherfrom the conductor.
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Electromagnetism (2 of 3)
The intensity and strength of magnetic linesof force increase proportionally with an
increase in current flow through a conductor.
Similarly, they decrease proportionally with adecrease in current flow through the
conductor.
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Electromagnetism (3 of 3)
A rule called the right-hand rule is used to
indicate the direction of
the magnetic lines of
force.
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Using Electromagnetism (1 of 2)
A magnetic field existswhen current flows
through a wire.
When the wire is
coiled, the magneticfield is intensified.
When an iron core is
placed in the center of
this coil, the magneticfield is further
intensified.
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Using Electromagnetism (2 of 2)
Magneto-motive forceis measured in ampere-
turns (at).
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Electrical Current Characteristics (1 of 2)
Direct current Current flows in one direction only.
Current flow may be:
Continuous Pulsed
DC current is used almost exclusively in
highway vehicles.
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Electrical Current Characteristics (2 of 2)
Alternating current Current cyclically
reverses at high
speed.
AC current is used inalternators and by
certain sensors.
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Sources of Electricity (1 of 2)
Chemical In a lead acid battery,
voltage is produced by
a chemical reaction
between lead and leadperoxide plates
submersed in sulfuric
acid.
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Sources of Electricity (2 of 2)
Static electricity Thermoelectric
Photoelectric
Piezoelectric
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Electromagnetic Induction
Electromagnetic induction Current is produced in a
conductor that is moved
through a stationary
magnetic field.
Current is produced whena magnetic field is moved
past a stationary
conductor.
Electromagnetic induction
is a means of convertingmechanical energy into
electrical energy.
Electrical Circuits
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Electrical Circuits
and Ohms Law (1 of 5)
Ohms law describes the relationshipbetween electrical potential, current, and
resistance.
An electrical circuit must have:
Power source
Path
Load
El t i l Ci it
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Electrical Circuits
and Ohms Law (2 of 5)
Voltage
Current
Resistance Circuit components
Power source
Conductors Switches
Circuit protection devices
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Electrical Circuits
and Ohms Law (3 of 5) Series circuits
There is a single path for current to flow.
All of the current flows through each resistor in
the circuit. Parallel circuits
There are multiple paths for current to flow.
The resistance in each path determines thecurrent flow through it.
Series parallel circuits
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Electrical Circuits
and Ohms Law (4 of 5) Electrical circuit terminology
Short circuit
Open circuit Grounds
Short to ground
High resistance circuits
El t i l Ci it
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Electrical Circuits
and Ohms Law (5 of 5) OHMS law states that an
electrical pressure of 1 voltis required to move 1 amp ofcurrent through a resistanceof 1 ohm.
E = I x R I = Intensity = current in
amps
E = EMF (electromotiveforce) = pressure in volts
R = resistance =
resistance in ohms This is a mathematical
formula that techniciansMUST know.
Ohms Law
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Applied to Series Circuits
All of the current flows
through all of the
resistances in the
circuit
Total circuit resistance
is the sum of all of the
resistances. Rt =R1+
R2etc
Ki hh ff L f C t
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Kirchhoffs Law of Current
Current flowing into ajunction or point in an
electrical circuit must
equal the current
flowing out.
Kirchhoffs Law of Voltage Drops
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Kirchhoffs Law of Voltage Drops
Voltage will drop inexact proportion to the
resistance, and the
sum of the voltage
drops must equal thevoltage applied to the
circuit.
Power
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Power
The unit for measuring power is the wattusually represented by the letter P.
P = I x E
1 horsepower (HP) = 746 watts
Electric Motor
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Electric Motor
and Generator Principle (1 of 3)
Electric Motor and
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Electric Motor and
Generator Principle (2 of 3)
DC motors
The electric motor converts
electrical energy into
mechanical energy.
Current-carryingconductors are arranged
as loops of wire in an
armature.
The armature is placed
inside a magnetic field.
When current flows
through the armature,
torque is produced.
Electric Motor
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Electric Motor
and Generator Principle (3 of 3)
Generators
A generator is simply an
electric motor with its
function reversed.
AC generators produce ACcurrent which must be
rectified to DC.
Reluctor-type generators
consisting of a permanent
magnet, a coil of wire, anda toothed reluctor are used
as shaft speed sensors.
Capacitance
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Capacitance
Capacitors storeelectrons.
A capacitor consists of
two conductors
separated by aninsulating material
called dielectric.
Types of Capacitors
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Types of Capacitors
Power supply filter Spike suppressant
Resistor-capacitor circuits (R-C circuits)
Coils Transformers and Solenoids
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Coils, Transformers, and Solenoids
Two coils are arranged so that one is subjectto a magnetic field created in the other.
The input coil is the primary coil.
The output coil is the secondary coil.
Step-up transformers have secondary coils
with a greater number of windings.
Step-down transformers have secondary coils
with a lower number of windings.
Solenoids and Magnetic Switches
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Solenoids and Magnetic Switches
Magnetic switches areused so that a low
current can control a
high current.
Solenoids use thesame operating
principle, but are used
to convert electrical
energy into mechanicalmovement.
Summary (1 of 7)
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Summary (1 of 7)
All matter is composed of atoms.
All atoms have an electrical charge.
When an atom is balanced (the number of protonsmatch the number of electrons), the atom can bedescribed as being in an electrically neutral state.
All matter is electrical in essence. Electricity concerns the behavior of atoms that have
become, for whatever reason, unbalanced orelectrified.
Electricity may be defined as the movement of freeelectrons from one atom to another.
Summary (2 of 7)
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Summary (2 of 7)
Current flow is measured by the number of freeelectrons passing a given point in an electrical circuitper second.
Electrical pressure or charge differential is measured involts, resistance in ohms, and current in amperes.
The magnetic properties of some metals such as ironare due to electron motion within the atomic structure.
A direct relationship exists between electricity andmagnetism.
Electromagnetic devices are used extensively onvehicles.
Summary (3 of 7)
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Summary (3 of 7)
Magneto-motive force (mmf) is a measure ofelectromagnetic field strength.
Its unit is ampere- turns (At).
Ohms law is used to perform circuit calculations onseries, parallel, and series-parallel circuits.
In a series circuit, there is a single path for currentflow and all of the current flows through eachresistor in the circuit.
A parallel circuit has multiple paths for current flow.
The resistance in each path determines the currentflow through it.
Summary (4 of 7)
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Summary (4 of 7)
Kirchhoffs law of voltage drops states that the sumof voltage drops through resistors in a circuit mustequal the source voltage.
When current is flowed through a conductor, amagnetic field is created.
Reluctance is resistance to the movement ofmagnetic lines of force. Iron cores have permeability and are used to reduce
reluctance in electromagnetic fields.
Capacitors are used to store electrons.
They consist of conductor plates separated by adielectric.
Summary (5 of 7)
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Summary (5 of 7)
Capacitance is measured in farads. Capacitors are rated by voltage and by capacitance.
When current is flowed through a wire conductor,
an electromagnetic field is created.
When the wire is wound into a coil, theelectromagnetic field strength is intensified.
The principle of a transformer can be summarized
by describing it as flowing current through a primary
coil and inducing a current flow in a secondary oroutput coil.
Summary (6 of 7)
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Summary (6 of 7)
Transformers can be grouped into three categories:
isolation, step-up, and step-down.
An electromagnetic switch is used in a truck
electrical circuit to enable a low-current circuit to
control a high-current circuit. A relay is an example of an electromagnetic switch.
A solenoid uses similar operating principles to an
electromagnetic switch except that it converts
electromagnetic energy into mechanical movement.
Summary (7 of 7)
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S y ( )
Solenoids are used extensively in truckelectrical circuits for functions such as starter
engage mechanisms, diesel electronic unit
injector control, automatic transmission clutch
controls, and suspension pilot switches.