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Inductors are not as well-known as resistors and capacitors, but they are still a critical and even fundamental part of circuits and electronics. In this article, we'll learn about inductors, how to handle them in AC and DC circuits, and discuss why they work the way they do, and in which applications you can encounter them.
What is an Inductor?
Physically, an inductor is just a coil of wire, an energy storage device that stores energy in an electric field generated by the current flowing through these coiled wires. But this coil can be packaged in a variety of ways, so an inductor can look like almost anything. Fortunately for the schematic, the variation is more limited, and all representations of the inductor are some variation of something that looks like a ring wire.
The ability to store energy in an electric field is measured in units of Henry, named after the man who discovered the principle of inductance. For most real-life scenarios, especially for electronic applications, most inductors are only a fraction of Henry's. Now that we've briefly covered what inductors are and what they look like, let's look at how they work in a circuit and why they're important.
How does an inductor work in a DC circuit?
In DC circuits, inductors are very simple to use. Simply replace any inductor in the steady-state DC circuit with a short circuit. This does not seem surprising if you remember that inductors are fundamentally coils. If the inductor is connected in parallel with other components, these elements can be ignored as it is like shorting their nodes together.
Inductors are slightly more complex in transient DC circuits, or circuits that measure what happens shortly after a change. The inductor is resistant to changes in current, so if there is a closed switch, and the voltage across the inductor starts to change from 0v, the voltage will change instantaneously, but it will take some time for the current passing through it to rise to its steady-state current.
The voltage is equal to the inductance multiplied by the rate of change passing through the inductor. Observe a steady-state DC signal where current flows continuously through the inductor and the voltage across the inductor is not visible. However, if you flip a switch and there is a voltage trying to drive current through the inductor, the inductor will "fight" the change in current by generating its own voltage.
So, for DC steady-state and transient circuits, you can think of inductors as short circuits, or they are resistant to current changes. To wrap it up, let's see how an inductor works in an AC circuit.
How does an inductor work in an AC circuit?
In AC circuits, the performance and behavior of an inductor depends on different factors. The way they affect a circuit depends on two things: the frequency of the signal in the circuit and the inductance of the components.
We can know the linear relationship between impedance and inductance. The higher the inductance, the higher the impedance, and the lower the inductance, the lower the impedance. Since the inductor resists changes in current, the inductor circuit "lags". This means that when the voltage at both ends of the circuit changes, the corresponding current passing through the circuit is delayed a little. So, if the voltage increases, it takes a little time for the current to increase. This can be strange because at the inflection point, the voltage moves in one direction, while the current continues to move in the other direction.
What is actually happening in an inductor?
We know that an inductor is just a coil. So, why does the shape of the wire cause this behavior?
It is important to remember that electrons actually have mass, and as a large collection, this can have a greater impact than one might expect. In fact, if we were able to create a tutorial on electromagnetic theory with extremely high frequency signals, a lot of time would be spent discussing how to deal with electrons getting where you want to be when they're moving fast.
But in the case of inductors, you can imagine how electrons can't turn well, and when they have to change direction frequently, they struggle, isn't that a metaphorical image?
An inductor, one of the most basic devices in a circuit, is a passive, two-terminal device that is easy to handle in an ideal DC circuit but becomes more complex as their impedance changes with frequency. And, as always, real life is always more challenging than the ideal situations we sometimes learn in class. With this foundation, you can now move on to more complex and powerful circuits!
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