An inductor is one of the simplest components in electronics, but its behaviour comes from a deep physical effect: a current creates a magnetic field, and changing that current induces a voltage that opposes the change.

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How an Inductor Works

1. Basic Idea

An inductor is usually a coil of wire. When electric current flows through it, it creates a magnetic field around the coil.

The key principle is electromagnetic induction:

A changing current produces a changing magnetic field →
a changing magnetic field induces a voltage that opposes the change.

This is known as Lenz’s Law.

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2. The Inductor’s Defining Equation

In ASCII form:

V = L * (dI/dt)

Where:

• V = voltage across the inductor
• L = inductance (in Henries)
• dI/dt = rate of change of current

This equation says:

• If you try to change the current quickly, the inductor produces a large opposing voltage.
• If the current is steady (dI/dt = 0), the inductor acts like a short circuit.

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3. What Inductors “Do” Physically

Store Energy

Inductors store energy in their magnetic field:

E = (1/2) * L * I^2

If the current stops suddenly, the collapsing magnetic field pushes current out — sometimes with a very high voltage.

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Resist Current Change

Inductors are “inertia for current.”
They don’t resist current itself — only changes in current.

Analogy:

• Capacitor = “spring” for voltage
• Inductor = “mass” for current

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4. Why a Coil?

A straight wire has a small inductance.
A coil concentrates and strengthens the magnetic field.

More turns → more inductance
Adding an iron/ferrite core → much more inductance

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5. Behaviour in Circuits

When connected to DC:

• At the instant of connection: inductor resists current
• After a while: behaves like a short (just the wire resistance)

When connected to AC:

• Higher frequency → higher opposition
  (because the current changes faster)

This opposition is called inductive reactance:

“” X_L = 2 * pi * f * L

So at higher frequencies, inductors behave more like resistors with increasing “resistance.”

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## **6. Inductors in RF Circuits**

Inductors are essential in:

- LC resonant circuits  

- Filters  

- Oscillators  

- Impedance matching networks  

- Transformers  

They pair with capacitors to create circuits that are sensitive to specific frequencies.

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## **7. Intuition Summary**

An inductor:

- Creates a magnetic field when current flows  

- Stores energy in that field  

- Pushes back against rapid changes in current  

- Lets low-frequency/steady current through easily  

- Resists high-frequency changes  

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If you like, I can follow up with:

- ASCII coil diagrams  

- Real-world examples (transformers, chokes, RF inductors)  

- How inductors behave at very high RF frequencies (e.g., parasitics, SRF)