Last updated on October 2nd, 2025 at 06:32 pm
Sunday the 28th was our fourth class. We cover the basics of magnetism and inductance.
Inductance: From High School Chalkboards to Everyday Engineering
When I first studied inductance back in high school in the 1980s, it all felt a bit abstract. We were told that electricity and magnetism were linked in curious ways, that a simple wire could resist changes in current, and that this mysterious thing called “back EMF” always seemed to push back against whatever we tried to do. At the time, it felt like a trick of the math more than a tangible reality.
Fast forward to today, and I see those same fundamentals in every transformer, motor, and circuit I encounter. The equations on the chalkboard have become the backbone of modern engineering practice.
The Basics Haven’t Changed
Inductance, at its core, is about resistance to change. Any conductor carrying current produces a magnetic field, and when that current changes, the magnetic field changes with it. Faraday showed us that a changing magnetic field induces a voltage, and Lenz’s law tells us that voltage will always oppose the change that created it. That’s why a conductor, whether straight or wound into a coil, pushes back against changes in current flow.
In a classroom, this was demonstrated with the right-hand rule and magnetic field lines circling a wire. Winding that wire into a coil concentrated the flux, boosting its ability to oppose current changes. Back then it was a curious property. Today, I see it as nature’s built-in safety feature.
Inductors in Action
This week’s presentation walked through inductance in both DC and AC circuits. With DC, inductance delays the rise of current until the magnetic field stabilizes. With AC, the story is more dynamic: the magnetic field is always changing, always inducing a voltage that resists the flow. The result is what we call inductive reactance—an opposition that grows with frequency.
This dual behaviour explains why inductors pass DC easily but can choke out higher-frequency signals. It’s the same principle that makes them indispensable in filters, power supplies, and countless control applications.
From Inductors to Transformers
Once coils are involved, it’s a short step to transformers. Here, changing currents in one coil induce voltages in another, enabling us to step voltages up or down, match impedances, or isolate circuits entirely.
The elegance of the turns ratio—primary to secondary—never ceases to impress me. Whether it’s a massive utility transformer or a tiny toroidal inductor on a circuit board, the same rules apply: ratios matter, losses must be managed, and efficiency is king. Even after all these years, I find the beauty of this simple, reliable relationship remarkable.
Enduring Lessons
Looking back, what strikes me most is how little these fundamentals have changed. The names—Faraday, Henry, Lenz—still echo through the equations, but the applications have multiplied beyond what I could have imagined as a teenager.
In high school, inductance was just another physics unit to get through before exams. Today, I see it as a quiet constant in my daily work—woven into motors, relays, solenoids, and transformers, underpinning so much of the technology we depend on.
The fundamentals of inductance have aged better than we have: steady, dependable, and still as sharp as ever.
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