Chapter 31

[object Object],[object Object],[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 31, the reader should be able to:

[object Object],KEY TERMS: Continued

ELECTRICITY ,[object Object],Figure 31–1 In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun in our solar system (right). Continued

[object Object],NOTE: As an example of relative sizes of parts of an atom, consider that if an atom were magnified so that the nucleus were the size of the period at the end of this sentence, the whole atom would be bigger than a house.

[object Object],Figure 31–2 The nucleus of an atom has a positive () charge and the surrounding electrons have a negative () charge. Continued These same + and  signs are used to identify parts of an electrical circuit. Neutrons have no charge at all. They are neutral.

[object Object],Figure 31–3 This figure shows a balanced atom. Continued

Figure 31–4 Unlike charges attract and like charges repel. ,[object Object],Continued

Figure 31–5 An unbalanced, positively charged atom (ion) will attract electrons from neighboring atoms.

[object Object],Figure 31–6 The hydrogen atom is the simplest atom, with only one proton, one neutron, and one electron. More complex elements contain higher numbers of protons, neutrons, and electrons. Continued If there are too many electrons for the first and closest shell to the nucleus, others will orbit in additional shells until all electrons have an orbit within a shell. There can be as many as seven shells around a single nucleus.

Figure 31–7 As the number of electrons increases, they occupy increasing energy levels that are further from the center of the atom. ,[object Object],Figure 31–8 Electrons in the outer orbit, or shell, can often be drawn away from the atom and become free electrons. Continued

[object Object],Figure 31–9 A conductor is any element that has one to three electrons in its outer orbit. Continued

[object Object],Figure 31–10 Copper is an excellent conductor of electricity because it has just one electron in its outer orbit, making it easy to be knocked out of its orbit and flow to other nearby atoms. This causes electron flow, which is the definition of electricity. Continued

[object Object],Pure water is an insulator; however, if anything is in the water, such as salt or dirt, then the water becomes conductive. Because it is difficult to keep water from becoming contaminated, water is usually thought of as being capable of conducting electricity, especially high voltage such as from household 110-volt or 220-volt outlets. Is Water a Conductor? Continued

[object Object],Figure 31–11 Insulators are elements with five to eight electrons in the outer orbit. Continued Insulators include plastics, wood, glass, rubber, ceramics (spark plugs), and varnish for covering (insulating) copper wires in alternators and starters.

[object Object],Figure 31–12 Semiconductor elements contain exactly four electrons in the outer orbit. Continued

[object Object],Figure 31–13 Current electricity is the movement of electrons through a conductor. Continued

Figure 31–14 Conventional theory states that current flows through a circuit from positive (+) to negative (-). Automotive electricity uses the conventional theory in all electrical diagrams and schematics. ,[object Object],This book uses the conventional theory unless stated otherwise. Discovery of the electron and its negative charge led to the electron theory , which states there is electron flow from negative to positive.

[object Object],Figure 31–15 One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a point in 1 second. Continued

[object Object],Figure 31–16 An ammeter is installed in the path of the electrons similar to a water meter used to measure the flow of water in gallons per minute. the ammeter displays current flow in amperes. ,[object Object],[object Object],[object Object],[object Object],Continued

[object Object],Figure 31–17 Voltage is the electrical pressure that causes the electrons to flow through a conductor.

[object Object],Figure 31–18 This digital multimeter set to read DC volts is being used to test the voltage of a vehicle battery. Most multimeters can also measure resistance (ohms) and current flow (amperes). Continued ,[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 31–19 Resistance to the flow of electrons through a conductor is measured in ohms. Continued

[object Object],Continued ,[object Object],[object Object],[object Object],[object Object]

Figure 31–20 A display at the Henry Ford Museum in Dearborn, Michigan, that includes a hand-cranked generator and a series of light bulbs. This figure shows a young man attempting to light as many bulbs as possible. The crank gets harder to turn as more bulbs light because it requires more power to produce the necessary watts of electricity. ,[object Object],Watts A watt is the electrical unit for power , the capacity to do work. Named for Scottish inventor, James Watt (1736–1819).

SOURCES OF ELECTRICIY ,[object Object],Continued Friction When certain different materials are rubbed together, the friction causes electrons to be transferred from one to the other. Both materials become electrically charged. These charges are not in motion but stay on the surface where they were deposited. Because the charges are stationary, or static, this type of voltage is called static electricity . Vehicle tires rolling on pavement often create static electricity that interferes with radio reception.

[object Object],Figure 31–21 Electron flow is produced by heating the connection of two different metals. Continued Some engine temperature sensors operate in this manner. This form of voltage is called thermoelectricity .

[object Object],Figure 31–22 Electron flow is produced by light striking a light-sensitive material. Photoelectricity is widely used in light-measuring devices such as photographic exposure meters and automatic headlamp dimmers. Continued

[object Object],Figure 31–23 Electron flow is produced by pressure on certain crystals. The voltage created is called piezoelectricity . Some automobile engine control sensors, such as the knock sensor (KS), use piezoelectricity to create voltage or to vary resistance and control a computer input signal. Continued

[object Object],Conductors and Resistance All conductors have some resistance to current flow. Several principles of conductors and their resistance include the following: ,[object Object],[object Object],Continued

[object Object],[object Object],Continued

CONDUCTION CHART ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],7. Brass (copper and zinc) 8. Platinum 9. Iron 10. Nickel 11. Tin 12. Steel 13. Lead Starting with the best… See this chart on Page 323 of your textbook. Continued

Figure 31–24 This figure shows a resistor color code interpretation. ,[object Object],Continued

[object Object],Figure 31–25 This figure shows a typical carbon resistor. Continued

[object Object],Figure 31–26 A three-wire variable resistor is called a potentiometer. Continued Potentiometers are most commonly used as throttle position (TP) sensors on computer-equipped engines.

Figure 31–27 A two-wire variable resistor is called a rheostat. ,[object Object]

SUMMARY ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Chapter 31

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Chapter 31