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.
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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
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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
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
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.
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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.
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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.
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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.
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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) _____________ _____
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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
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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? ________________________________________
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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. _________________________
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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?
______________________________________________________________________________________
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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
__________________________________________.
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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. _________________________________
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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
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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
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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
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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 =
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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.
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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
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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 =
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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.
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