Chapter 5

Fundamentals of Electricity

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 by the number of electrons in their outer shells.

• Outline the properties of conductors, insulators, and semiconductors.

• Describe the characteristics of static electricity.

Objectives (2 of 3)

• Define what is meant by the conventional and electron 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.

Objectives (3 of 3)

• Outline the components required to construct a typical electrical circuit.

• Perform electrical circuit calculations using Ohm’s law.

• Identify the characteristics of DC and AC.• Describe some methods of generating a

current flow in an electrical circuit.• Describe and apply Kirschhoff’s first and

second laws.

Atomic Structure and Electron Movement (1 of 7)

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 are defined by the number of electrons in their outer shells.

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 matter

called protons.• Neutrons

– The nucleus contains matter with no charge called neutrons.

• Electrons– Negatively charged particles called electrons are

orbiting each atomic nucleus.

Atomic Structure and Electron Movement (4 of 7)

• Electrons orbit the nucleus in concentric paths called shells.

• All electrons are alike -- AND -- all protons are alike.– So where is the difference?

• Every chemical element has a distinct identity and is made up of distinct atoms.– That is, each has a different number of

protons and electrons.

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.

Atomic Structure and Electron Movement (6 of 7)

• Electrons (negative charge) are held in their orbital shells by the nucleus (positive charge) of the atom.

• Electrons are prevented from colliding with each other because they all have similar negative charges that tend to repel each other.

• A molecule is a chemically bonded union of two or more atoms.

• A compound is a chemically bonded union of atoms of two or more dissimilar elements.

Atomic Structure and Electron Movement (7 of 7)

• All atoms have an electrical charge. • An atom is balanced when the number of protons

match the number of electrons and is said to be in an electrically neutral state.

• Electricity is concerned with the behavior of atoms that have become unbalanced or electrified.

• Electricity may be defined as the movement of free electrons from one atom to another.

• Current flow is a measurement of the number of free electrons passing a given point in an electrical circuit per second.

Conductors and Insulators (1 of 4)

• Electron movement through a conductor is referred to as current.

• To produce current flow, electrons must move from atom to atom.

Conductors and Insulators (2 of 4)

• A conductor is generally a metallic element that contains fewer than four electrons in its outer shell or valence. – Copper, aluminum,

gold, silver, iron, and platinum are classified as conductors.

Conductors and Insulators (3 of 4)

• An insulator is a nonmetallic substance that contains five or more electrons in its outer shell or valence. – Glass, mica, rubber,

and plastic are good insulators.

Conductors and Insulators (4 of 4)

• Semiconductors are a group of materials that cannot be classified either as conductors or insulators.– They have exactly four

electrons in their outer shell.

– Silicon (Si) is an example of a semiconductor.

Current Flow (1 of 3)

• Conventional theory states that current flows from positive to negative.

• Vehicle schematics use conventional theory almost exclusively.

Current Flow (2 of 3)

• When the electron was discovered, scientists revised the theory of current flow and called it electron theory.

• The electron theory states that current flow is from negative to positive.

Current Flow (3 of 3)

• Charge differential or voltage 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 of current flow.

Magnetism (1 of 3)

• A bar shaped permanent 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.

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) determines the magnetic force.

Magnetism (3 of 3)

• The flux density is always greatest at the poles 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.

Electromagnetism (1 of 3)

• Current flow through any conductor creates a magnetic field.

• Magnetic lines of force do not change when the current flow through a conductor is constant.

• When current flow increases, the lines of force will extend further from the conductor.

Electromagnetism (2 of 3)

• The intensity and strength of magnetic lines of force increase proportionally with an increase in current flow through a conductor.

• Similarly, they decrease proportionally with a decrease in current flow through the conductor.

Electromagnetism (3 of 3)

• A rule called the right-hand rule is used to indicate the direction of the magnetic lines of force.

Using Electromagnetism (1 of 2)

• A magnetic field exists when current flows through a wire.

• When the wire is coiled, the magnetic field is intensified.– When an iron core is

placed in the center of this coil, the magnetic field is further intensified.

Using Electromagnetism (2 of 2)

• Magneto-motive force is measured in ampere-turns (at).

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.

Electrical Current Characteristics (2 of 2)

• Alternating current– Current cyclically

reverses at high speed.

– AC current is used in alternators and by certain sensors.

Sources of Electricity (1 of 2)

• Chemical– In a lead acid battery,

voltage is produced by a chemical reaction between lead and lead peroxide plates submersed in sulfuric acid.

Sources of Electricity (2 of 2)

• Static electricity

• Thermoelectric

• Photoelectric

• Piezoelectric

Electromagnetic Induction

• Electromagnetic induction– Current is produced in a

conductor that is moved through a stationary magnetic field.

– Current is produced when a magnetic field is moved past a stationary conductor.

– Electromagnetic induction is a means of converting mechanical energy into electrical energy.

Electrical Circuits and Ohm’s Law (1 of 5)

• Ohm’s law describes the relationship between electrical potential, current, and resistance.

• An electrical circuit must have:– Power source– Path– Load

Electrical Circuits and Ohm’s Law (2 of 5)

• Voltage

• Current

• Resistance

• Circuit components– Power source– Conductors– Switches– Circuit protection devices

Electrical Circuits and Ohm’s 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 the

current flow through it.• Series parallel circuits

Electrical Circuits and Ohm’s Law (4 of 5)

• Electrical circuit terminology– Short circuit– Open circuit– Grounds– Short to ground– High resistance circuits

Electrical Circuits and Ohm’s Law (5 of 5)

• OHM’S law states that an electrical pressure of 1 volt is required to move 1 amp of current through a resistance of 1 ohm.

• E = I x R– I = Intensity = current in

amps– E = EMF (electromotive

force) = pressure in volts– R = resistance =

resistance in ohms• This is a mathematical

formula that technicians MUST know.

Ohm’s Law 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 + R2 etc…

Kirchhoff’s Law of Current

• Current flowing into a junction or point in an electrical circuit must equal the current flowing out.

Kirchhoff’s Law of Voltage Drops

• Voltage will drop in exact proportion to the resistance, and the sum of the voltage drops must equal the voltage applied to the circuit.

Power

• The unit for measuring power is the watt usually represented by the letter P.– P = I x E– 1 horsepower (HP) = 746 watts

Electric Motor and Generator Principle (1 of 3)

Electric Motor and Generator Principle (2 of 3)

• DC motors– The electric motor converts

electrical energy into mechanical energy.

– Current-carrying conductors 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 and Generator Principle (3 of 3)

• Generators– A generator is simply an

electric motor with its function reversed.

– AC generators produce AC current which must be rectified to DC.

– Reluctor-type generators consisting of a permanent magnet, a coil of wire, and a toothed reluctor are used as shaft speed sensors.

Capacitance

• Capacitors store electrons.

• A capacitor consists of two conductors separated by an insulating material called dielectric.

Types of Capacitors

• Power supply filter

• Spike suppressant

• Resistor-capacitor circuits (R-C circuits)

Coils, Transformers, and Solenoids

• Two coils are arranged so that one is subject to 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

• Magnetic switches are used so that a low current can control a high current.

• Solenoids use the same operating principle, but are used to convert electrical energy into mechanical movement.

Summary (1 of 7)

• All matter is composed of atoms.• All atoms have an electrical charge.

– When an atom is balanced (the number of protons match the number of electrons), the atom can be described 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 or electrified.

• Electricity may be defined as the movement of free electrons from one atom to another.

Summary (2 of 7)

• Current flow is measured by the number of free electrons passing a given point in an electrical circuit per second.

• Electrical pressure or charge differential is measured in volts, resistance in ohms, and current in amperes.

• The magnetic properties of some metals such as iron are due to electron motion within the atomic structure.

• A direct relationship exists between electricity and magnetism. – Electromagnetic devices are used extensively on

vehicles.

Summary (3 of 7)

• Magneto-motive force (mmf) is a measure of electromagnetic field strength.– Its unit is ampere- turns (At).

• Ohm’s law is used to perform circuit calculations on series, parallel, and series-parallel circuits.

• In a series circuit, there is a single path for current flow and all of the current flows through each resistor in the circuit.

• A parallel circuit has multiple paths for current flow.– The resistance in each path determines the current

flow through it.

Summary (4 of 7)

• Kirchhoff’s law of voltage drops states that the sum of voltage drops through resistors in a circuit must equal the source voltage.

• When current is flowed through a conductor, a magnetic field is created.

• Reluctance is resistance to the movement of magnetic 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 a dielectric.

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, the

electromagnetic 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 or output coil.

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)

• Solenoids are used extensively in truck electrical circuits for functions such as starter engage mechanisms, diesel electronic unit injector control, automatic transmission clutch controls, and suspension pilot switches.