Chapter 5

1. Chapter 5 Fundamentals of Electricity

2. 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.

3. 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.

4. 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.

5. Atomic Structure and Electron Movement (1 of 7)

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. Current Flow (1 of 3) • Conventional theory states that current flows from positive to negative. • Vehicle schematics use conventional theory almost exclusively.

17. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. Electromagnetism (3 of 3) • A rule called the right-hand rule is used to indicate the direction of the magnetic lines of force.

25. 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.

26. Using Electromagnetism (2 of 2) • Magneto-motive force is measured in ampere-turns (at).

27. 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.

28. Electrical Current Characteristics (2 of 2) • Alternating current • Current cyclically reverses at high speed. • AC current is used in alternators and by certain sensors.

29. 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.

30. Sources of Electricity (2 of 2) • Static electricity • Thermoelectric • Photoelectric • Piezoelectric

31. 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.

32. 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

33. Electrical Circuits and Ohm’s Law (2 of 5) • Voltage • Current • Resistance • Circuit components • Power source • Conductors • Switches • Circuit protection devices

34. 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

35. Electrical Circuits and Ohm’s Law (4 of 5) • Electrical circuit terminology • Short circuit • Open circuit • Grounds • Short to ground • High resistance circuits

36. 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.

37. 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…

38. Kirchhoff’s Law of Current • Current flowing into a junction or point in an electrical circuit must equal the current flowing out.

39. 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.

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

41. Electric Motor and Generator Principle (1 of 3)

42. 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.

43. 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.

44. Capacitance • Capacitors store electrons. • A capacitor consists of two conductors separated by an insulating material called dielectric.

45. Types of Capacitors • Power supply filter • Spike suppressant • Resistor-capacitor circuits (R-C circuits)

46. 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.

47. 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.

48. 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.

49. 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.

50. 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.