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Solution Manual for Delmar's Standard Textbook of Electricity, 5th Edition

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    ’s Guide to Accompany DELMAR’S STANDARD TEXTBOOK OF ELECTRICITY Fifth Edition by Stephen L. Herman and Kerry A. Reinhackel SOLUTIONS GUIDE

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    iii Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Section 1 Safety, Basic Electricity, and Ohm’s Law . . . . . . . . . . . . . . . . . . . . . . . . 1 Unit 1 Atomic Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Unit 2 Electrical Quantities and Ohm’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Unit 3 Static Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Unit 4 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Unit 5 Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Section 2 Basic Electric Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Unit 6 Series Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Unit 7 Parallel Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Unit 8 Combination Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Unit 9 Kirchhoff’s Laws, Thevenin’s, Norton’s, and Superposition Theorems . . . . . 20 Section 3 Meters and Wire Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Unit 10 Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Unit 11 Using Wire Tables and Determining Conductor Sizes . . . . . . . . . . . . . . . . . 27 Section 4 Small Sources of Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Unit 12 Conduction in Liquids and Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Unit 13 Batteries and Other Sources of Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Unit 14 Magnetic Induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Section 5 Basics of Alternating Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Unit 15 Basic Trigonometry and Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Unit 16 Alternating Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Section 6 Alternating Current (AC) Circuits Containing Inductance . . . . . . . . . . 43 Unit 17 Inductance in AC Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Unit 18 Resistive-Inductive Series Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Unit 19 Resistive-Inductive Parallel Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

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    iv Section 7 AC Circuits Containing Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Unit 20 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Unit 21 Capacitance in AC Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Unit 22 Resistive-Capacitive Series Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Unit 23 Resistive-Capacitive Parallel Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Section 8 AC Circuits Containing Resistance-Inductance-Capacitance . . . . . . . . 61 Unit 24 Resistive-Inductive-Capacitive Series Circuits . . . . . . . . . . . . . . . . . . . . . . . . 61 Unit 25 Resistive-Inductive-Capacitive Parallel Circuits . . . . . . . . . . . . . . . . . . . . . . 64 Unit 26 Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Section 9 Three-Phase Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Unit 27 Three-Phase Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Section 10 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Unit 28 Single-Phase Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Unit 29 Three-Phase Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Section 11 DC Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Unit 30 DC Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Unit 31 DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Section 12 AC Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Unit 32 Three-Phase Alternators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Unit 33 Three-Phase Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Unit 34 Single-Phase Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Answers to Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Answers to Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

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    v This ’s Guide has been divided into five main sections to help you in the instruction process. The first section is an overview of instruction techniques and information on learner types. The second section in- cludes teaching instructions for each of the 34 units of the text. The third section includes answers and solu- tions to the review questions. The fourth section con- tains 15 tests that can be used at various intervals in the instruction process. The final section includes answers to the tests. This lesson plan manual has been written with the idea that many of the instructors using Delmar’s Stan- dard Textbook of Electricity have not had an opportu- nity to take a course in education. With this in mind, a variety of ideas to help the instructor teach the material has been written into the section-by-section lesson plans. Additionally, this introduction will give the instructor a brief overview of the four main types of learners and ways to enable those types of learners to be successful in the classroom. This success in the classroom will, ultimately, lead to success out in the field. There are four basic types of learning strategies that most people use to learn new material. Some individuals may use more than one of these strategies, but most will use at least one, whether they are aware of it or not. The first type I will discuss is the visual learner. Visual learners use what they see to help them under- stand what is being taught. This goes beyond just read- ing a text. In fact, visual learners may not benefit as much from the printed word as they do from pictures, graphs, charts, and other examples drawn about what is written in the text. For this type of learner there are in- structions concerning visual aids throughout this entire manual. Many people are visual learners, often in com- bination with one or more of the other learning styles, such as audile. An audile learner will listen carefully to everything the instructor has to say. Depending on the memory ca- pabilities of this type of learner, he or she may also take quite a few notes. This type of learner may ask for in- formation or explanations to be repeated, or restated in a different way. If this individual also uses the strategies of the visual learner, then explanations that are simple, clear, and are accompanied by visual aids benefit them the most. They may do just fine right where they sit. For the kinesthetic learner, though, this may not be the case. A kinesthetic learner is a hands-on type of learner. These individuals like to hold the visual aids in their hands and work things out (like experiments) with their hands. They will want to create a circuit and connect the wires, resistors, and so on. They will also benefit, as will the visual learners, from drawing their own circuits and diagrams. They may or may not be good at compre- hending the material just from reading the text, as tactile learners will be. Tactile learners are good readers and can compre- hend most of the material that they need to learn by reading the text. Tactile learners, however, will also greatly benefit from the use of visual aids, hands-on activities, and clear concise explanations. As often as possible, the instructor should try to fol- low the lesson plans, bring in visual aids, make charts, and use the discussions to uncover any prior knowledge that students may have about each unit. Individuals learn better when they believe that they already have some knowledge on a subject that they are beginning to study. With this in mind, each unit has a statement that calls for a question/discussion time that will include allowing students to realize that they prob- ably are much more familiar with the overall subject matter than they thought they were. Think of it as wall- paper being hung on a wall. The wallpaper simply sticks better, and more readily, if there is already some paste or glue on the wall. Our minds are the same way. This prior knowledge, uncovered and made known to a student, is the glue that gives your lesson something to stick to. It sticks better, faster, and more readily when the student has been made aware that the glue is there. The slight- est amount of glue is always going to hold something better than no glue at all. Each unit is completed with a Unit Round Up sec- tion. This is where you will always need to double-check for understanding. Just in case the glue didn’t hold, and your lesson slid off onto the floor, you will have students Introduction

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    vi explain concepts to you, work out formulas, and explain why the various things work as they do. The best way to check for understanding is to have the students give back to you, in their own words, what you have given to them. In the case of the various formulas, practice is the key. It will be useful if you can create some problems of your own for your students to solve, using the formulas that are being covered in any given unit. This manual was written with you in mind. It has been written in user-friendly language and is meant to be a benefit and aid to you as a teacher. Obviously, any idea that has been given as a lesson enhancer is optional. Every learning group is different, and one group may require everything you can come up with to help them grasp the material, and other groups may barely require your pres- ence! Use what will help you and pass over what will not.

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    1 SECTION 1 Safety, Basic Electricity, and Ohm’s Law OUTLINE S-1 General Safety Rules S-2 Effects of Electric Current on the Body S-3 On the Job S-4 Protective Clothing S-5 Ladders and Scaffolds S-6 Fires S-7 Ground-Fault Circuit Interrupters S-8 Grounding KEY TERMS Meter De-energized circuit Idiot proofing Horseplay Artificial respiration Cardiopulmonary resuscitation Milliamperes Fibrillation OSHA MSDS Confined spaces Lockout and tagout Fire-retardant clothing Scaffolds Energized circuit Disconnected Safety Overview Anticipatory Set Go over the eleven objectives of this unit and ask students what they already know about any of the objectives men- tioned. Promote classroom discussion on the subject of safety. Be careful to correct any mistakes. ANSWER TO REVIEW QUESTIONS 1. To think before acting 2. To prevent a current path directly through the heart. 3. 0.1–0.2 amperes 4. When the heart quivers or vibrates and does not pump blood. 5. It discharges a capacitor across the heart causing the heart of contract. 6. The Secretary of Labor 7. To ensure safe and healthy workplaces in the U.S. 8. Material safety data sheet 9. The electrician 10. 4 feet 11. A current path to ground other than intended. 12. 5 mA 13. Circuit breaker, receptacle, extension cord 14. Class B fires involve fuels such as grease, combustible liquids or gases. 15. NEC Section 250

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    2 Anticipatory Set To prepare students for this unit, begin by stating the four objectives of the unit. Then, ask students what they already know about any of the four objectives. You may need to do a little prompting, such as asking what they re- member or know about atoms, positive/negative charges, things that conduct electricity, or things that do not con- duct electricity. Ask if anyone knows why you don’t use electrical tools in the rain, or why you do use rubber boots to protect you from shock when working on a damp floor. 1-1 Early History of Electricity Instruct students to be prepared to define key terms in their notes as you proceed through the unit. Briefly discuss the two basic types of current. Follow up with a brief explanation of repulsion and attraction. Have some examples from list A or B (p. 30 of text) to show these principles in action. Distinguish between negative and positive charges as they relate to attraction and repulsion. Ask students if they know any other examples. Check for understanding by asking one or more students to explain the attraction/repulsion process. 1-2 Atoms Define an atom. Discuss the three principle parts of the atom, and discuss the role of each part as it relates to the make-up of the 90 natural elements and 23 artificial elements. Check for understanding before moving on. 1-3 The Law of Charges Begin discussion of the law of charges with a reminder of the principles of attraction/repulsion. This will help the students to immediately begin using previous learning as building blocks on which to attach new information. This is a good time to explain that everything in this text will build on principles learned, unit by unit. Discuss charges that attract and charges that repel. Using the PowerPoint ® presentation, follow the outward-going and inward-going charges. Explain the two theories about why protons having the same charge do not break apart in the nucleus. Check for un- derstanding. Have students draw the proton-electron relationship and the proton-proton relationship in their notes. 1-4 Structure of the Atom Ask students for to explain the similarities between how the planets orbit the sun in the solar system and the man- ner which electrons orbit the center of the atom. Point out that both the planets and electrons exist in exact specific orbits determined by their size (mass) and speed. UNIT 1 Atomic Structure OUTLINE 1-1 Early History of Electricity 1-2 Atoms 1-3 The Law of Charges 1-4 Structure of the Atom 1-5 Electron Orbits 1-6 Valence Electrons 1-7 Electron Flow 1-8 Insulators 1-9 Semiconductors 1-10 Molecules 1-11 Methods of Producing Electricity 1-12 Electrical Effects KEY TERMS Alternating current (AC) Atom Atomic number Attraction Bidirectional Conductor Direct current (DC) Electron Electron orbit Element Insulators Matter Molecules Negative Neutron Nucleus Positive Proton Repulsion Semiconductors Unidirectional Valence electrons

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    3 1-5 Electron Orbits The section on electron orbits may call for a review of some basic mathematics. When discussing electron orbits, be sure that students understand how to determine the maximum number of elec- trons that can be in any given orbit. To check for understanding of the 2(N) 2 formula, write some arbitrary possibil- ities on the board or overhead: 2(5) 2 , 2(3) 2 , 2(8) 2 , and so on. Have students tell you how many electrons are in the orbit, and the number of the orbit, or shell: 50/5th orbit, 18/3rd orbit, 128/8th orbit, and so on. Stop here, and review the definitions of all key terms covered in the first five sections: direct current, alternating cur- rent, repulsion, attraction, atom, matter, element, electron, neutron, proton, quarks, nucleus, atomic number, opposite and like charges, and gluon. Have students explain these various terms. Review how they are related to each other. 1-6 Valence Electrons Explain valence electrons and explain that the inner shells will have more electrons than the valence shell, as ex- plained with 2(N) 2 . Good examples of this are PowerPoint slides corresponding to Figures 1–15 and 1–16 . Explain how atoms with fewer valence electrons make better update conductors and why atoms with a higher number of va- lence electrons resist conductivity. 1-7 Electron Flow Discuss electron flow using the cue ball example. Ask students to give other examples (shuffle board, croquet, etc.). Be sure that students understand the directional flow of the energy from the impacting electron and how that energy is split by this directional flow, lessening the energy flow in each direction. 1-8 Insulators Review what the maximum number of valence electrons is (8) and how this results in the creation of insulators. Have students give examples of insulators used in various professions (boots, gloves, etc.) or in household appliances (electrical cords). 1-9 Semiconductors Explain semiconductors and give examples of how they are used (in computers, for example). 1-10 Molecules Define molecules, and have students distinguish between molecules and atoms. See if students can explain, using what they have learned about electrons and valence shells, how two atoms might form a compound. 1-11 Methods of Producing Electricity Go over, one by one, each of the ways to produce electricity. Discuss the benefits of using one way over another, for a particular purpose. Point out terms the student should become familiar with, such as piezo, Seebeck, photons, pho- tovoltaic, photoemissive, photoconductive, solar cells, and cad cells . Take some time to discuss the production of electricity from light, as it is so widely used. 1-12 Electrical Effects Discuss how electricity can create some of the various effects, heat, light, pressure, magnetism, and chemical reac- tions that it is created from. Give examples of the various uses of electricity, in these ways. For example, if you have ac- cess to a crystal radio or earphone, it would be extremely beneficial for the student to see this process in action. Perhaps you can copper plate something, or discuss the difference in buying gold plated jewelry versus solid gold jewelry. Per- haps a discussion of the way electrolysis is used would also be helpful. Having a variety of light bulbs, of different wattages, might be a good way for students to explain how light is produced, and the results in heat watts and light watts. Unit Round Up Review all terms from the unit, including those terms covered in Sections 1-6 through 1-10: valence electrons, conductor, electron flow, insulators, semiconductors, and molecules. Review basic principles covered in the unit, and check for understanding by having students explain to you how these principles work. It is also a good idea for the instructor to review the test from the ’s Guide to assure that all necessary material was covered well enough for students to answer all test questions.

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    4 At No Seq Sym Name 1 1 H Hydrogen 2 2 He Helium 3 3 Li Lithium 4 4 Be Beryllium 5 5 B Boron 6 6 C Carbon 7 7 N Nitrogen 8 8 O Oxygen 9 9 F Fluorine 10 10 Ne Neon 11 11 Na Sodium 12 12 Mg Magnesium 13 13 Al Aluminum 14 14 Si Silicon 15 15 P Phosphorous 16 16 S Sulfur 17 17 Cl Chlorine 18 18 Ar Argon 19 19 K Potassium 20 20 Ca Calcium 21 21 Sc Scandium 22 22 Ti Titanium 23 23 V Vanadium 24 24 Cr Chromium 25 25 Mn Manganese 26 26 Fe Iron 27 27 Co Cobalt 28 28 Ni Nickel 29 29 Cu Copper 30 30 Zn Zinc 31 31 Ga Gallium 32 32 Ge Germanium 33 33 As Arsenic 34 34 Se Selenium 35 35 Br Bromine 36 36 Kr Krypton 37 37 Rb Rubidium 38 38 Sr Strontium 39 39 Y Yttrium 40 40 Zr Zirconium 41 41 Nb Niobium 42 42 Mo Molybdenum 43 (1) Tc Technetium 44 43 Ru Ruthenium 45 44 Rh Rhodium 46 45 Pd Palladium 47 46 Ag Silver 48 47 Cd Cadmium 49 48 In Indium 50 49 Sn Tin 51 50 Sb Antimony 52 51 Te Tellurium 53 52 I Iodine 54 53 Xe Xenon 55 54 Cs Cesium 56 55 Ba Barium 57 56 La Lanthanum 58 57 Ce Cerium 59 58 Pr Praseodymium At No Seq Sym Name 60 59 Nd Neodymium 61 (2) Pm Promethium 62 60 Sm Samarium 63 61 Eu Europium 64 62 Gd Gadolinium 65 63 Tb Terbium 66 64 Dy Dysprosium 67 65 Ho Holmium 68 66 Er Erbium 69 67 Tm Thulium 70 68 Yb Ytterbium 71 69 Lu Lutetium 72 60 Hf Hafnium 73 71 Ta Tantalum 74 72 W Tungsten 75 73 Re Rhenium 76 74 Os Osmium 77 75 Ir Iridium 78 76 Pt Platinum 79 77 Au Gold 80 78 Hg Mercury 81 79 Tl Thallium 82 80 Pb Lead 83 81 Bi Bismuth 84 82 Po Polonium 85 83 At Astatine 86 84 Rn Radon 87 85 Fr Fracium 88 86 Ra Radium 89 87 Ac Actinium 90 88 Th Thorium 91 89 Pa Proactinium 92 90 U Uranium 93 (3) Np Neptunium 94 (4) Pu Plutonium 95 (5) Am Americium 96 (6) Cm Curium 97 (7) Bk Berkelium 98 (8) Cf Californium 99 (9) Es Einsteinium 100 (10) Fm Fermium 101 (11) Md Mendelevium 102 (12) No Nobelium 103 (13) Lr Lawrencium 104 (14) Rf Rutherfordium 105 (15) Db Dubnium 106 (16) Sg Seaborgium 107 (17) Bh Bhorium 108 (18) Hs Hassium 109 (19) Mt Meitnerium 110 (20) Uun Ununnilium 111 (21) Uuu Unununium 112 (22) Uub Ununbium 114 (23) Uuq Ununquadium Seq—sequence—plan number is natural element. Number in parentheses is artificial element.

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    5 UNIT 2 Electrical Quantities and Ohm’s Law OUTLINE 2-1 The Coulomb 2-2 The Ampere 2-3 The Electron Flow Theory 2-4 The Conventional Current Flow Theory 2-5 Speed of Current 2-6 Basic Electric Circuits 2-7 The Volt 2-8 The Ohm 2-9 The Watt 2-10 Other Measures of Power 2-11 Ohm’s Law 2-12 Metric Prefixes KEY TERMS Ampere (A) British thermal unit (Btu) Complete path Conventional current flow theory Coulomb (C) Electromotive force (EMF) Electron flow theory Grounding conductor Horsepower (hp) Impedance Joule Neutral conductor Ohm ( Ω ) Ohm’s law Potential difference Power Resistance Volt (V) Watt (W) Anticipatory Set Go over the eight objectives of this unit and ask students what they already know about any of the objectives men- tioned. Be careful to correct any mistakes. For example, a student may tell you that an amp is something that he plugs his guitar into. You might even hear that an ohm is a sound you make when meditating! A little humor here relaxes the students and creates a classroom environment geared to active learning. Begin a question/answer session on the various types of measurements that students are already familiar and comfortable with. Tell them that this unit is sim- ply an explanation of a set of measurements for electricity. 2-1 The Coulomb Explain that the coulomb is a quantity measurement. A good visual aid is a 1- or 2-liter bottle of soda water. Show the students that it is the amount of soda water in the bottle that makes the measurement of 2 liters an accurate one. This is what “quantity” measurement means. Using that same 2-liter bottle, let it represent 1 coulomb tossed into the Pacific Ocean. As you define Coulomb’s law of electrostatic charges, write the equation on the board. Use two items to put into the Q 1 and Q 2 positions. Also, inform students what a dielectric constant is and how dielectric breakdown can occur. 2-2 The Ampere Explain that an ampere is simply another measurement unit: 1 coulomb per second. Explain the two types of measurement involved in the ampere: quantity and time. Refer to the PowerPoint slide corresponding with Figure 2–1 to show how an ampere of current flows through a wire when 1 coulomb flows past a point in 1 second. Illustrate this by using the cue ball or another item that will roll or slide easily. Place a coin on top of a desk and roll or slide your visual aid past the coin. Explain that the moving object represents a coulomb, the coin is the point it passes, and an ampere of electricity is what flowed through the unseen wire on the desktop. So, the ampere is the measurement of the amount (quantity) of electricity flowing through a circuit. Also, refer students to Figure 2–2 in the text, making the water flow comparison.

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    6 2-3 The Electron Flow Theory Briefly state what the electron flow theory is, and draw the theory on the board showing this type of flow. Emphasize that this theory is the one that will be used throughout the text. 2-4 The Conventional Current Flow Theory Explain this theory carefully, making sure that students take note of the difference in flow: + to - versus - to + in the two theories. Discuss why the conventional flow theory is preferred. Use the car battery example and check for understanding. Remember to double check for understanding on the direction that electrons always flow, and make sure the students know that the electron theory is the one that will be used throughout this text. 2-5 Speed of Current Establish with students that a current is the flow of electrons through a conductive substance. Refer to the exam- ple with the table-tennis balls in Figure 2–6 . Try to acquire a piece of 3/4-inch or 1-inch pipe and some table-tennis balls. Doing this visually in class will sink home the message of the nearly instantaneous effect of electrical impulses. Also, remind students to try to count how long it takes a bulb to light up once a switch has been flipped. Here is a flow of electrons, the current having been activated by flipping the switch, and the speed of that flow is so fast that the bulb lights up before our hand is off the switch! 2-6 Basic Electric Circuits Explain closed circuits and open circuits. Emphasize the loop quality of a closed circuit. Refer back to the light switch example to illustrate how a switch is used to open a circuit when not in use, and to close a circuit when it is in use. Explain how short circuits occur, and why proper circuits and proper insulators must be used to prevent wires forming unintended short circuits. Now, add to this the explanation on grounded circuits. Have a three-prong plug or adapter to show students during this explanation. Be sure to distinguish between the grounding conductor and the neutral conductor. 2-7 The Volt Define volt for the class and distinguish it from an ampere. An ampere is a quantity measurement of electricity flowing through a circuit, whereas a volt is the pressure, or electromotive force, that pushes those electrons through a wire. If you refer back to the pipe and the table-tennis balls, a volt is the ball that hits the last ball in line, forcing the first ball in line out of the pipe. Explain the potential aspect of the volt and define a joule (J) for the class, letting them know that they will see this word again in the discussion of watts (W). Check for understanding by having students explain that voltage pushes current through a wire but does not actually flow through the wire, as an ampere does. Students should realize that voltage is a potential force pushing electricity along a current waiting to be activated. As an example, note that the wall socket has voltage, or potential, but to release that force a circuit must be activated by plugging something into that socket. 2-8 The Ohm Define ohm for the class. Refer to Figure 2–12 and Figure 2–13 in the text, and use the text’s example of running on the beach to explain resistance. To further illustrate resistance, use the comparison of weight lifting. The more weight you try to lift, the more your body resists the weight. Your body does this to protect you. An ohm serves a similar function in controlling the flow of electrons in an electric circuit. Just as your muscles would short-circuit on you under too much pressure, the electric circuit will short out with a power overload. 2-9 The Watt Define wattage and compare it to the ampere. Make the point that both of these are quantity measurements, but the watt is the power flow resulting from the electric flow (amperes) times the force applied to that flow (volts). Wattage is not a flow of current; it is a resulting amount of power.

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    7 Explain the need for energy conversion to occur before true power (watts) can exist. The electrical energy flowing through a circuit must be converted into another type of energy. Use the example of a young but extremely active child. The parent may enroll that child in several sports-related activities to convert wild or destructive energy into focused and purposeful energy. With electricity, that conversion can be to heat energy or mechanical energy. 2-10 Other Measures of Power Explain the definition of horsepower (hp). A drawing, even a primitive one, will be helpful. Draw a horse, with a rope hooked to a harness on the horse. Have the rope go up and through a pulley, and attach the rope to a weight. Change the poundage amount of the weight to work the formula several times. This visual aid will help students grasp the definition of horsepower. Then, show the equality of horsepower to watts. Define British thermal unit (Btu), and compare it to the calorie in the metric system. Discuss what a joule is again, and that 1 joule = 1 watt/second. Refer to Figure 2–17, and have students copy this conversion chart into the front of their notebooks for easy access, or make copies of this chart, and perhaps all conversion charts included in this text, and distribute to students. Have students work the sample problem, then add people (a few at a time, at an average weight of 160 lbs. each), and have students figure the amount of hp needed for each new weight. Continue with these examples until the class is comfortable with this formula. Then, practice with the Btu formula and use other examples, changing the high tem- perature desired and/or the amount of the water to be heated. 2-11 Ohm’s Law Go over Ohm’s law carefully, and have students explain what it means. Students can get confused if they don’t break it down one section at a time. For clarification, go over each of the three formulas, making sure students un- derstand that the level of resistance is equal to the number of ohms. Next, show students how they can solve for R, I, or E, if they have the two components that make up the missing amount. For example, show students that if they know the I and R, they can find the E (E = I × R). If they need to find I, they can divide R into E. If they need to find R, they divide I into E. Practice all three of these formulas sev- eral times until students are comfortable with them. A quick memory tool that your students can use here is the triangle: E I R Students can see that I = E/R, that R = E/I, and that E = R × I. It is a handy reminder of the three formulas. Display the formula chart in Figure 2–20 on the overhead. Explain how the chart can be used, based on the infor- mation they have. Do several practice problems using this “Dial-A-Formula” chart, covering the examples given in the text. 2-12 Metric Prefixes If your students are like most Americans, just the mention of the metric system can cause them to break out in a cold sweat. This lack of knowledge concerning the metric system can lead to learning blocks whenever the metric system is involved. As a teacher, you must help students overcome this anxiety. Explain that you are only concerned with a very basic knowledge of the metric system, and either have students copy the chart from Figure 2–24, or have a handout that they can put into their notebooks near the front for easy access. They also need to copy the chart from Figure 2–25. Unit Round Up Take as much time as is necessary to review this unit. It is a vitally important unit. Students need to be able to work with the various concepts and formulas comfortably and use them interchangeably. Go through the summary to- gether, and assign the review questions to double-check for complete understanding. Check these assignments before moving to the next unit to see if any reteaching needs to be done. Review all key terms from the unit.

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    8 ANSWERS TO PRACTICAL APPLICATIONS 1. Yes the circuit is large enough. 20 A × 0.80 = 16 A. 500 W × 8 = 4000 W. 4000 W/277 V = 14.44 A. 2. The first problem is that the circuit is too small to operate the furnace (15,000 W/240 V = 62.5 A). The cir- cuit breaker does not always trip because the heating strips come on in stages. The third stage may not always turn on. The problem will have to be solved by connecting a larger circuit breaker and probably a larger conductor size to the furnace. The circuit breaker must be larger than 78.125 A (15,000 W/240 V = 62.5 A) (62.5 A × 1.25 = 78.125 A). 3. Three fans can be connected to a single 15-ampere circuit. Two circuits will be required. Since the loads are continuous duty, the circuit current is limited to 80% of the circuit rating or 12 amperes (15 × 0.80 = 12). Each fan contains four 60-watt lamps for a total of 240 watts. The current draw for the lamps is 2 amperes (240/120 = 2). The motor current of 1.8 amperes makes a total of 3.8 amperes per fan (2 + 1.8 = 3.8). Each circuit could supply power to 3.16 fans (12/3.8 = 3.16). 4. Yes, the 20-ampere circuit can supply power to both the lamp and the motor. Continuous circuit current is 16 amperes for a 20-ampere circuit (20 × 0.80). The 600-watt lamp has a current draw of 5 amperes (600/120) and the motor current is 8.5 amperes. Total circuit current is 13.5 amperes. UNIT 3 Static Electricity OUTLINE 3-1 Static Electricity 3-2 Charging an Object 3-3 The Electroscope 3-4 Static Electricity in Nature 3-5 Nuisance Static Charges 3-6 Useful Static Charges KEY TERMS Electroscope Electrostatic charges Lightning Lightning arrestor Lightning bolts Lightning rods Nuisance static charges Precipitators Selenium Static Thundercloud Useful static charges Anticipatory Set Unit 3 is a very basic, simple unit. Go over the objectives and ask students to share experiences they have had in- volving static electricity. Have some visual aids on hand to help illustrate the principles of electrostatic charges. These aids might include a rubber rod, a piece of wool, a plastic comb, some tissues, an inflated balloon, and some pictures you copied on a copy machine. When you make these copies, make them progressively darker so that you can show the process in even more vivid detail. 3-1 Static Electricity As you discuss the various uses of static electricity, and include the explanation of precipitators, ask students to name a household item that may use this process (an air-conditioning unit). Be sure that students understand what static means, and that it is a charge, not a current. It is similar to voltage in that it is a charge waiting to be released, as a volt is potential force waiting for a current to push. Also, point out the electron theory in action here. Be sure that students realize that insulators hold electrons, and that is why electrostatic charges build on them. Make sure students understand that a lack of electrons means a majority of protons and, thus, a positive charge. The inverse of this also needs to be explained.

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    9 3-2 Charging an Object Explain that this is merely an extension of the principles discussed in the first section. Here, we use these princi- ples to electrostatically charge items by choice. Have students experiment with visual aids, building up static charges. The comb can be run through someone’s dry hair and then used to pick up pieces of the tissue. The balloon can be rubbed on someone’s dry hair (or on the wool) and then suspended on a wall. 3-3 The Electroscope Describe an electroscope and explain its function. If it is possible, have an electroscope in the classroom. Students could use the various things they used earlier and determine what type of charge the various items took on. 3-4 Static Electricity in Nature Define lightning as the result of static electricity, discuss why the flow of electricity sometimes moves from the clouds to the ground, and explain that it goes the other way at other times. Again, the electron theory explains this upward or downward movement. Explain what lightning rods are, and make the distinction between them and lightning arrestors. Refer to Figures 3–9, 3–10, and 3–11 in the text to help illustrate those explanations. 3-5 Nuisance Static Charges Basically, just briefly touch on this, referring back to the things you did in Section 3-2. These principles have al- ready been discussed. However, ask your students to explain why the various types of products that can be put in the dryer with wet clothes (Bounce, Downy Dryer Sheets, Cling, etc.) prevent the static from building up in the clothes. Ask them why an aerosol spray product made for this purpose can eliminate static cling when sprayed directly on the clothing. Ask why some clothing items cling together, while others do not (e.g., rayon socks do, but denim jeans do not; pantyhose do, but heavy towels do not). 3-6 Useful Static Charges Discuss the various useful ways in which static electricity is used. When explaining how the copy machine works, display your series of progressively darker copies. Have students explain how the copies became progressively darker (beyond the obvious answer of pushing the button to make them darker). Unit Round Up Summarize the unit, review all key terms, and double-check for understanding. If necessary, go back through any previous explanations, using the visual aids. UNIT 4 Magnetism OUTLINE 4-1 The Earth Is a Magnet 4-2 Permanent Magnets 4-3 The Electron Theory of Magnetism 4-4 Magnetic Materials 4-5 Magnetic Lines of Force 4-6 Electromagnetics 4-7 Magnetic Measurement 4-8 Magnetic Polarity 4-9 Demagnetizing 4-10 Magnetic Devices

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    10 KEY TERMS Ampere-turns Demagnetized Electromagnets Electron spin patterns Flux Flux density Left-hand rule Lines of flux Lodestones Magnetic domains Magnetic molecules Magnetomotive force (mmf) Permanent magnets Permeability Reluctance Residual magnetism Saturation Anticipatory Set This is another unit in which students will greatly benefit from several visual aids. Gather magnets of various sizes, some cardboard (even several sheets of paper stacked together will work), some paper clips, and perhaps a model, or actual, electromagnet. Use PowerPoint presentation Figures 4–2, 4–5, 4–6, 4–7, 4–10, 4–11, 4–14, 4–15, and 4–17. State the unit objectives. 4-1 The Earth Is a Magnet Give the explanation of true geographic north versus magnetic north. Have students draw Figure 4–2 into their notes, labeling the four poles, the polar axis, and magnetic flux lines. After they draw Figure 4–2 into their notes, ex- plain why a compass points toward true magnetic north instead of to geographic north. Have students look at their drawing as you explain this. 4-2 Permanent Magnets Define permanent magnets, and have some to show your students (even if they came off your refrigerator and have a phone number for ordering pizza on them, or a pig, or a cow, etc.). Be sure students write the definition of a per- manent magnet into their notes, as well as the basic law of magnetism given in this section. 4-3 The Electron Theory of Magnetism Explain electron spin patterns and how they affect, or account for, the magnetic qualities or lack of magnetic qual- ities in an object. Refresh students’ memories by reminding them that the valence shell and, therefore, the valence electrons are at the outermost contact points of an atom. The valence shell is the outermost shell, or orbit, of an atom. Explain magnetic domains or magnetic molecules, and how these are formed by iron, nickel, and cobalt sharing electrons in a way that does not cancel out their magnetic fields. Have students refer to Figures 4–5 through 4–7, and use these PowerPoint slides. 4-4 Magnetic Materials Discuss the three classifications of magnetic materials. Explain what an alloy is, and why it makes better permanent magnets. Perhaps students can figure it out for themselves, just in knowing what the alloy Alnico 5 is made of. Refer them to the Ferromagnetic materials list, and ask them to explain why Alnico 5 makes such a good permanent magnet. Discuss ceramic magnets and, if possible, show some examples to the class. 4-5 Magnetic Lines of Force Explain what flux is, and have students make note of its symbol in their notes. If you have the magnets and iron fil- ings, this is the time to use them to display flux lines in action. If you do not have these items, use Figures 4–10 and 4–11 to illustrate this process. Make sure students understand that magnetic lines of flux never cross each other but repel each other instead. Also, have students make note of another basic law of magnetism: like poles repel and unlike poles attract. 4-6 Electromagnetics Explain how a magnetic field is formed and how electric current is necessary to produce the magnetic field. Remind students that permanent magnets maintain their magnetism without electrical current, whereas electromag- nets usually do not.

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