Notes:
Don't give your students the equation with which to perform this calculation! Let them find it on their own. The [di/dt] notation may be foreign to students lacking a strong mathematical background, but don't let this be an obstacle to learning! Rather, use this as a way to introduce those students to the concept of rates of change, and to the calculus concept of the derivative.

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Notes:
Ahhh, the controversy of conventional versus electron flow. The existence of two contradicting conventions for denoting direction of electric current irritates me to no end, especially when the one upon which almost all electronic device symbolism is based on is actually incorrect with regard to charge flow through metallic conductors (the majority case in electric circuits)! Your students will surely encounter both "conventional" and ëlectron" flow in their careers, so be sure to introduce them to both conventions.
Discuss with your students the consequences of winding resistance in real inductors. Is it significant? Work together with your students to calculate how much extra voltage would be dropped across the inductor, based on their research on the typical winding resistance of a 4 henry inductor (ask them where they obtained the information!), given a [di/dt] rate of 1.5 amps per second.
Ask your students if they think it might be possible to create an inductor with no ßtray" resistance at all to interfere with perfect, theoretical inductor behavior. What would be required to make the "perfect" inductor?

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Notes:
If your students are having difficulty answering the follow-up question in the Answer, ask them to compare these voltage figures (45 V and 11.25 V) against the voltage that would be dropped by just one of the 5 H inductors under the same condition (an applied current changing at a rate of 4.5 amps per second).
It is, of course, important that students know how series-connected and parallel connected inductors behave. However, this is typically a process of rote memorization for students rather than true understanding. With this question, the goal is to have students come to a realization of inductor connections based on their understanding of series and parallel voltages and currents.

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Notes:
Ask your students this question: given capacitors and inductors, which of these component types behave more like resistors, in terms of their series versus parallel equivalent values?

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Notes:
It is most helpful to first draw a schematic diagram for this inductor network before trying to perform any inductance calculations, in order that a clear understanding of the series/parallel connections be established.

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Notes:
Inductors tend to be even more scarce than resistors in regard to the availability of different values, so knowing how to combine different inductors together to achieve a desired total inductance is a practical skill.
It should be noted to your students that inductors may interact with one another if placed too close, due to the magnetic field of one inductor "linking" with the coil of another inductor. This is called mutual inductance, and if present alters the otherwise straightforward series-parallel inductance relationships that one would expect to be analogous to series-parallel resistances.

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Notes:
Power system reactors are usually installed in substations, where they appear as coils of wire (no iron core) a few feet in diameter, usually located near circuit breakers.

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�

Red, Grn, Brn, Gld = 250 mH, +/- 5%

�

Wht, Org, Red, Sil = 9300 mH, +/- 10%

�

Grn, Gry, Blk = 58 mH, +/- 20%

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Vio, Blu, Org, Gld = 76 mH, +/- 5%

Notes:
Students will note a lot of similarities between the inductor color code and the resistor color code, but they should also note one significant difference!

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Notes:
Have your students actually test a few inductors with their ohmmeters in class. Unlike capacitor checking with an ohmmeter, there is never a substantial "charging" period! If your students have already learned about capacitor checking with an ohmmeter, ask them to explain why there is no "charging" action indicated by the ohmmeter when connected to an inductor.
If there were an observable "charging" time exhibited by an inductor when measured by an ohmmeter, what would it appear as, in terms of the ohmmeter's indication?
Normally, I don't give away answers to follow-up questions in the "Notes" section, but here I feel it may be necessary. Studies have shown that inductors have about an equal chance of failing open as they do failing shorted. Of course, this will vary with the specific design and application of the inductor, but there is no mode of failure clearly more probable than the other.

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Notes:
Ask your students to identify what condition(s) might lead to a condition of saturation. And, even if the extreme ends of the B-H curve are avoided, what does the nonlinear shape of the B-H plot indicate about the linearity of an inductor? The inductance formula (e = L[di/dt]) assumes perfect linearity, but is this really true for an inductor whose core exhibits this kind of magnetic flux/force relationship?

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Notes:
The purpose of this question is to get students to kinesthetically interact with the subject matter. It may seem silly to have students engage in a ßhow and tell" exercise, but I have found that activities such as this greatly help some students. For those learners who are kinesthetic in nature, it is a great help to actually touch real components while they're learning about their function. Of course, this question also provides an excellent opportunity for them to practice interpreting component markings, use a multimeter, access datasheets, etc.

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