Inductance Electronics Lesson Plan Performance Objective Upon completion of this assignment, the student will be able to demonstrate an understanding of inductance concepts by correctly performing the procedures outlined on the lab activity handouts and by scoring at least 70 % on the Inductance Exam. Specific Objectives Describe inductance Define terms associated with inductance Name three scientific laws dealing with inductance Describe the meaning of scientific laws including Oersted’s Law, Faraday’s Law, and Lenz’s Law Identify factors contributing to self-inductance Recall formulas associated with inductance Identify factors that affect the amount of inductance of a coil Identify factors that determine mutual inductance Identify facts about transformer ratios Demonstrate the ability to determine transformer ratios Terms Inductor- a device (usually a coil) that introduces inductance into an electrical circuit. Inductance- the property of an electric circuit where a varying current induces an electromotive force (EMF) in that circuit or another circuit. Self-inductance- the property of an electric circuit when an EMF is induced back into itself by a change of circuit current. Henry- the unit of inductance. Permeability- the measure of the ease with which material will pass lines of flux. Mutual inductance- the property of two circuits whereby an EMF is induced in one circuit by a change of current in the other. Coupling coefficient- a number indicating the fraction of flux lines of one circuit cutting another circuit. Transformer- a device that transfers a changing current and voltage from one circuit to another through inductive coupling. Time It should take approximately three, 45-minute class periods to teach the lesson and one 45-minute lab. Copyright © Texas Education Agency, 2014. All rights reserved. 1 Preparation TEKS Correlations This lesson, as published, correlates to the following TEKS. Any changes/alterations to the activities may result in the elimination of any or all of the TEKS listed. Electronics 130.368 (c) o (3) The student develops skills for managing a project. The student is expected to: (A) use time-management techniques to develop and maintain work schedules and meet deadlines; (B) complete work according to established criteria; and (C) participate in the organization and operation of a real or simulated engineering project. o (5) The student implements the concepts and skills that form the technical knowledge of electronics using project-based assessments. The student is expected to: (B) demonstrate an understanding of magnetism and induction as they relate to electronic circuits; and (C) demonstrate knowledge of the fundamentals of electronics theory. o (6) The student applies the concepts and skills to simulated and actual work situations. The student is expected to: (B) apply electronic theory to generators, electric motors, and transformers. Interdisciplinary Correlations Physics 112.39 (c) o (5) Science concepts. The student knows the nature of forces in the physical world. The student is expected to: (A) research and describe the historical development of the concepts of gravitational, electromagnetic, weak nuclear, and strong nuclear forces; (D) identify examples of electric and magnetic forces in everyday life; (E) characterize materials as conductors or insulators based on their electrical properties; (F) design, construct, and calculate in terms of current through, potential difference across, resistance of, and power used by electric circuit elements connected in both series and parallel combinations; and (G) investigate and describe the relationship between electric and magnetic fields in applications such as generators, motors, and transformers. Occupational Correlation (O*Net – www.onetonline.org/) Job Title: Electrical Engineers O*Net Number: 17-2071.00 Copyright © Texas Education Agency, 2014. All rights reserved. 2 Reported Job Titles: Electrical Engineer, Electrical Design Engineer, Project Engineer, Electrical Controls Engineer, Test Engineer, Hardware Design Engineer, Broadcast Engineer, Circuits Engineer, Electrical and Instrument Maintenance Supervisor (E and I Maintenance Supervisor), Electrical Project Engineer Tasks Prepare technical drawings, specifications of electrical systems, or topographical maps to ensure that installation and operations conform to standards and customer requirements. Operate computer-assisted engineering or design software or equipment to perform engineering tasks. Confer with engineers, customers, or others to discuss existing or potential engineering projects or products. Direct or coordinate manufacturing, construction, installation, maintenance, support, documentation, or testing activities to ensure compliance with specifications, codes, or customer requirements. Design, implement, maintain, or improve electrical instruments, equipment, facilities, components, products, or systems for commercial, industrial, or domestic purposes. Prepare specifications for purchases of materials or equipment. Perform detailed calculations to compute and establish manufacturing, construction, or installation standards or specifications. Investigate customer or public complaints, determine nature and extent of problem, and recommend remedial measures. Oversee project production efforts to assure projects are completed on time and within budget. Plan or implement research methodology or procedures to apply principles of electrical theory to engineering projects. Soft Skills Critical Thinking Active Listening Complex Problem Solving Active Learning Writing Reading Comprehension Time Management Monitoring Speaking Judgment and Decision Making Social Perceptiveness Accommodations for Learning Differences These lessons accommodate the needs of every learner. Modify the lessons to accommodate your students with learning differences by referring to the files found on the Special Populations page of this website. Preparation Review the slide presentation and this lesson document prior to each class Review and become familiar with the terminology and the example problems Have materials and handouts ready prior to the start of the lesson Copyright © Texas Education Agency, 2014. All rights reserved. 3 Have parts and equipment ready before lab References Buchla, D. and Floyd, T. (2004). The science of electronics DC/AC. Upper Saddle River, NJ: Prentice Hall. Floyd, T. (2009). Principles of electric circuits: Electron flow version. Upper Saddle River, NJ: Prentice Hall. Instructional Aids Inductance slide presentation and notes Lab Activity #1 Assignment #1 Assignment #2 Assignment #3 Assignment #4 Inductance Exam Inductance Exam Key Introduction The purpose of the lesson is for students to be able to demonstrate an understanding of inductance concepts. Say o Now that we have an understanding of magnetism, we need to understand the relationship between electricity and magnetism. Ask o We know about electromagnets, can anybody give me examples of other things or situations where electricity and magnetism are related? Ask o Electricity and magnetism cause motors and generators to work, but did you know that a magnetic field is created around any wire conducting electricity? Show o A motor (like a portable drill) Say o The reason this motor works is because electricity is converted into a magnetic field using the principle of inductance. Copyright © Texas Education Agency, 2014. All rights reserved. 4 Outline MI OUTLINE NOTES TO TEACHER I. Slide presentation A. Introduction B. Overview C. Terms and definitions D. Symbols and units Begin Inductance slide presentation. Slides 1-5 II. Laws involving induction A. These laws are based on the historical discovery of the links between electricity and magnetism. B. Oersted’s Law deals with a current creating a magnetic field around a conductor. C. Faraday’s law deals with the creation of electricity from magnetism. D. Lenz’s Law deals with how induced electricity compares to the originating electricity (selfinduction) or magnetism (mutual induction). Slides 6-13 III. What is Inductance A. The property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the amount of current. B. An inductor is not a linear device like a resistor. C. Inductance works two ways as described in Oersted’s Law and Faraday’s Law. D. When we say “inductance opposes a change in current,” that means that when the applied voltage creates an increased current through a linear device like a resistor, the inductor opposes that increase. E. When the applied voltage creates a decreasing current in a linear device, the inductor returns energy back to the circuit which maintains current. Slides 14-18 Inductance can be a difficult concept to explain. The slide notes can help explain these difficult concepts. Copyright © Texas Education Agency, 2014. All rights reserved. 5 MI OUTLINE IV. Inductors A. An inductor is a coil of wire either wrapped around air or some type of iron core. B. The core material is determined in part by how much inductance is wanted and the range of current used. C. Inductors in series add inductance values, the same as resistors in series. D. Inductors in parallel divide using the 1 over X formula, the same as resistors in parallel. V. Transformers A. A transformer’s turn ratio is used to identify both the voltage ratio and the current ratio. B. The voltage ratio is directly proportional to the turns ratio. C. The current ratio is inversely proportional to the turns ratio. D. Power in equals power out. E. Power equals voltage times current (P=VI). VI. Presentation summary and material review VII. Lab and worksheet assignments A. Lab Activity #1 - Determine Transformer Ratios B. Assignment #1 C. Assignment #2 D. Assignment #3 E. Assignment #4 VIII. Inductance Exam NOTES TO TEACHER Slides 19-24 Slides 25-27 Slides 25 and 26 are both turns ratio with different diagrams used to show both the schematic symbol and pictorial diagram of a coil. Slide 26 Then the student will answer the discussion question at the end of each lab and turn the lab activity and assignments sheets in for evaluation. Use Assignment #1- #4 Answer Key to grade assignments. Use the Inductance Exam Key to grade the exam. A minimum 70% is required on the exam. Copyright © Texas Education Agency, 2014. All rights reserved. 6 Multiple Intelligences Guide Existentialist Interpersonal Intrapersonal Kinesthetic/ Bodily Logical/ Mathematical Musical/Rhythmic Naturalist Verbal/Linguistic Visual/Spatial Application Guided Practice The students will observe, ask questions, and analyze the demonstration to be presented by the teacher. The teacher will use materials as listed in the lab activities to instruct how to read, measure, and record data as needed. Independent Practice The students will perform the lab and answer the discussion questions in Lab Activity #1 and Assignments #1 through #4 and will turn them in for evaluation. Summary Review Students will quiz each other on terms and concepts using flash cards. Evaluation Informal Assessment The teacher will ask questions and observe students working in the lab. Formal Assessment Students will complete the lab and assignments; they will also take the Inductance Exam. Enrichment Extension The use of the multimeter to accurately measure voltage, current, resistance, and power can be used to develop technical problem-solving skills needed in the workplace. Copyright © Texas Education Agency, 2014. All rights reserved. 7 Name______________________________________Class:_________________Date:____/____/____ Inductance Lab Activity #1 – Determine Transformer Ratios Equipment and materials Filament transformer (step down approximately 110v to 6v) Autotransformer or signal generator 30-ohm, 5W resistor Multimeter Electrical wire to build circuit Procedure 1. Construct the following circuit (Figure 1) 2. Adjust the signal input to 100 volts 3. Close the switch and record the secondary current, (IS) 4. Measure and record the primary voltage, (VP) _______ _____ 5. Measure and record the secondary voltage, (VS) ______ ____ 6. Measure and record the load resistor (approximately 30 ohms) _______ 7. Compare the measured secondary current (IS), with that obtained using Ohm’s law (VS/RL), and explain the difference ______________________________________________________________________ 8. Measure and record (IP) _____________ _____ Copyright © Texas Education Agency, 2014. All rights reserved. 8 Name______________________________________Class:_________________Date:____/____/____ 9. Use the voltage ratio and (IP) to compute (IS), then compare with measured (IS) values obtained in Steps 3 and 7________________________________________________________________________ 10. Calculate the turns ratio of the transformer ________________________________________________ ____________________________________________________________________________________ 11. Remove the load resistor and leave the secondary open 12. Measure and record the primary current (IP), with an open secondary _________________ _____ 13. Compare your voltage ratio with that indicated by this transformer manufacturer 14. Turn off circuit, disconnect components, and place materials in the proper storage area Copyright © Texas Education Agency, 2014. All rights reserved. 9 Name______________________________________Class:_________________Date:____/____/____ Inductance Assignment #1 I. Match the statement with their effects. 1._____ Source current increased A Inductance and induced EMF oppose current 2._____ Source current decreased B Inductance and induced EMF sustain current II. Match the phrases with their effects. 3._____ Decreased core permeability A Inductance increased 4._____ Add turns to a coil B Inductance decreased 5._____ Increase cross-sectional area of core 6._____ Decrease length of core III. Place an “X” next to statements that correctly finish this phrase: In an inductive circuit when the switch is suddenly opened, 7._____ the magnetic field around the coil begins to collapse. 8._____ current tries to continue to flow due to induced voltage. 9._____ current decays rather than abruptly going to zero. 10._____ all of the above are correct. 11. What is another name for induced voltage? ________________________________________ Copyright © Texas Education Agency, 2014. All rights reserved. 10 Name______________________________________Class:_________________Date:____/____/____ IV. True or False 12.__________ The induced voltage caused by inductance opposes any change in circuit current. 13.__________ The induced voltage is called CEMF. V. Name three different core materials used in inductor construction. 14. _________________________ 15. _________________________ 16. _________________________ Copyright © Texas Education Agency, 2014. All rights reserved. 11 Name______________________________________Class:_________________Date:____/____/____ Inductance Assignment #2 1. Find LT in this circuit (assume no mutual inductance). 1._______________________________________ 2. Solve for LT. 2.________________________________________ 3. Solve for LT. 3.________________________________________ 4. Solve for LT. 4.________________________________________ 5. L = CEMF If CEMF equals 100 volts when a change in current of 5000 amperes di/dt per second occurs, how much inductance is present? ______________________________________________________________________________________ Copyright © Texas Education Agency, 2014. All rights reserved. 12 Name______________________________________Class:_________________Date:____/____/____ Inductance Assignment # 3 1. Which pair of coils has the greatest mutual inductance (A) or (B)? (Assume everything except the spacing to be identical.) A_____ B_____ 2. In Problem one, is the coil with the greatest coefficient of coupling (A) or (B)? __________ 3. The coefficient of coupling between two coils is found to be 0.2. If the coils both have 4mh of inductance, the mutual inductance is A. ___________________________________________. (HINT: LM = k √ ) B. If the coils are connected in series and the inductance is aiding, the total inductance is __________________________________________. C. If the coils are connected in series and the inductance is opposing, the total inductance is __________________________________________. Copyright © Texas Education Agency, 2014. All rights reserved. 13 Name______________________________________Class:_________________Date:____/____/____ Inductance Assignment #4 – Transformer Ratios Given The above schematic is a perfect transformer (that is, the coupling coefficient is 1). The primary has 100 turns and the secondary has 400 turns. A 400-ohm load is across the secondary. Use the correct formula to find the answers to the following problems: 1. Secondary voltage, VS = _______________________ 2. Secondary current, IS = _______________________ 3. Primary current, IP = _______________________ 4. Power in the secondary circuit, PS = ____________________________ 5. Power in the primary circuit, PP = _____________________________ 6. The transformer is a (step-up) (step-down) transformer. _________________________________ Copyright © Texas Education Agency, 2014. All rights reserved. 14 Inductance Assignments #1 - #4 Answer Key Assignment #1 1. A 2. B 3. B 4. A 5. A 6. A 7. through 10. All have X’s (all are true) 11. Counter electromotive force (CEMF) 12. True 13. True 14. through 16. Air, iron, ferrite, or powdered iron (any three) Assignment #2 1. LT = L1 + L2 = 10mh + 5mh = 15mh 2. LT = L1 x L2 = 10h x 5h = 50 = 3.33h L1 + L2 10h + 5h 15 3. LT = 4. = = 100 / 20 = 5h + + = + + = , LT = 5 mh 5. L = CEMF = 100 v = 0.02 h or 20 mh di/dt 5000 a/sec Copyright © Texas Education Agency, 2014. All rights reserved. 15 Assignment #3 1. B 2. B 3. A. LM = = k √ = 0.2 x 4mh = 0.8mh B. LT = L1 + L2 + 2LM = 4mh + 4mh + 2(.8) = 9.6mh C. LT = L1 + L2 – 2LM = 4mh + 4mh – 2 (.8) = 6.4mh Assignment #4 1. VS = NS / NP x VP = 400 / 100 x 100v = 400v 2. IS = Vs / RL = 400v / 400Ω = 1a 3. IP = NS / NP x IS = 400/100 x 1a = 4a 4. PS = VS x IS = 400v x 1a = 400w 5. PP = VP x IP = 100v x 4a = 400w 6. Step-up Copyright © Texas Education Agency, 2014. All rights reserved. 16 Name______________________________________Class:_________________Date:____/____/____ Inductance Exam Match the terms with their correct definitions: 1. Inductor A The property of an electric circuit when an EMF is induced in that circuit by a change of current 2. Inductance B The unit of inductance 3. Self-inductance C A device that transfers changing current and voltage from one circuit to another by inductive coupling 4. Henry D The property of an electric circuit when a varying current induces an EMF in that circuit or another circuit Match the terms with their correct definitions: 5. Permeability A A number indicating the fraction of flux lines of one circuit cutting another circuit 6. Mutual inductance B A device that transfers changing current and voltage from one circuit to another by inductive coupling 7. Coupling coefficient C The property of two circuits whereby an EMF is induced in one circuit by a change of current in the other 8. Transformer D The measure of ease with which material will pass lines of flux Match the inductance unit abbreviations with their correct definitions: 9. L A Inductance 10. k B Henry 11. di/dt C Rate of current change 12. h D Coefficient of coupling 13. µ E Permeability Copyright © Texas Education Agency, 2014. All rights reserved. 17 Name______________________________________Class:_________________Date:____/____/____ 14. Which of the following statements is true concerning Lenz’s law? A Induced voltage is called electromotive force (EMF) B Induced voltage is so important that it is the basis of Ohm’s law C Induced voltage is called counter electromagnetic input (CEMI) D Induced voltage at every instant opposes any change in circuit current 15. Which of the following statements is true concerning factors affecting inductance of coils? A Number of turns- Inductance varies directly with the square of the number of turns B Permeability of core- Inductance varies inversely with the permeability of the core C Cross-sectional area of core- Inductance varies inversely with the cross-sectional area of the core D Length of core- Inductance varies directly with the length of the core 16. Which of the following does not identify this kind of inductor? A powdered iron B air C ferrite D iron Match the formulas for total inductance of inductors connected in series or in parallel to their correct definition: 17. Two inductors in parallel (different values) A LT = L + L + L3 + … 18. Three different value inductors in parallel B LT = L1 x L2 = L1 + L2 19. Three inductors of same value in series C 1 = 1 + 1 + 1 = LT L1 L2 L3 20. Three inductors of same value in parallel D LT = L / N = Copyright © Texas Education Agency, 2014. All rights reserved. 18 Name______________________________________Class:_________________Date:____/____/____ Match the formula to what it is used for. 21. = CEMF di/dt A solves for mutual inductance opposing 22. = k √ B solves for mutual inductance aiding 23. = L1 + L2 + 2LM C solves for Henry 24. = L1 + L2 – 2LM D solves for turns ratios 25. = NS / NP E solves for mutual inductance 26. Which of the following statements is true concerning transformer ratios? A In the step down transformer, NP is smaller than NS. B Turns ratio is the ratio of number of turns in secondary winding to number of turns in the primary winding (NS/NP). C Current ratio, IS/IP, equals voltage or turns ratio. D Power ratio, PO / PI, power in is less than power out. Copyright © Texas Education Agency, 2014. All rights reserved. 19 Inductance Exam Answer Key Match the terms with their correct definitions: 1. Inductor C A The property of an electric circuit when an EMF is induced in that circuit by a change of current 2. Inductance D B The unit of inductance 3. Self-inductance A C A device that transfers changing current and voltage from one circuit to another by inductive coupling 4. Henry B D The property of an electric circuit when a varying current induces an EMF in that circuit or another circuit Match the terms with their correct definitions: 5. Permeability D A A number indicating the fraction of flux lines of one circuit cutting another circuit 6. Mutual inductance C B A device that transfers changing current and voltage from one circuit to another by inductive coupling 7. Coupling coefficient A C The property of two circuits whereby an EMF is induced in one circuit by a change of current in the other 8. Transformer D The measure of ease with which material will pass lines of flux B Match the inductance unit abbreviations with their correct definitions: 9. L A A Inductance 10. k D B Henry 11. di/dt C C Rate of current change 12. h B D Coefficient of coupling 13. µ E E Permeability Copyright © Texas Education Agency, 2014. All rights reserved. 20 14. Which of the following statements is true concerning Lenz’s law? A Induced voltage is called electromotive force (EMF) B Induced voltage is so important that it is the basis of Ohm’s law C Induced voltage is called counter electromagnetic input (CEMI) D Induced voltage at every instant opposes any change in circuit current 15. Which of the following statements is true concerning factors affecting inductance of coils? A Number of turns- Inductance varies directly with the square of the number of turns B Permeability of core- Inductance varies inversely with the permeability of the core C Cross-sectional area of core- Inductance varies inversely with the cross-sectional area of the core D Length of core- Inductance varies directly with the length of the core 16. Which of the following does not identify this kind of inductor? A powdered iron B air C ferrite D iron Match the formulas for total inductance of inductors connected in series or in parallel to their correct definition: 17. Two inductors in parallel (different values) B A LT = L + L + L3 + … 18. Three different value inductors in parallel C B LT = L1 x L2 = L1 + L2 19. Three inductors of same value in series A C 20. Three inductors of same value in parallel D D 1 = 1 + 1 + 1 = LT L1 L2 L3 LT = L / N = Copyright © Texas Education Agency, 2014. All rights reserved. 21 Match the formula to what it is used for: 21. = CEMF di/dt C A solves for mutual inductance opposing 22. = k √ E B solves for mutual inductance aiding 23. = L1 + L2 + 2LM B C solves for Henry 24. = L1 + L2 – 2LM A D solves for turns ratios 25. = NS / NP D E solves for mutual inductance 26. Which of the following statements is true concerning transformer ratios? A In the step down transformer, NP is smaller than NS. B Turns ratio is the ratio of number of turns in secondary winding to number of turns in the primary winding (NS/NP). C Current ratio, IS/IP, equals voltage or turns ratio. D Power ratio, PO / PI, power in is less than power out. Copyright © Texas Education Agency, 2014. All rights reserved. 22