Understanding Inductors and Inductance — How Magnetic Energy Is Stored

In electronic circuits, not all components respond instantly to changes. Some store energy and react over time. One such fundamental component is the inductor, which stores energy in a magnetic field and resists changes in current.

In this blog, we’ll understand what an inductor is, how it works, how it stores energy, and what inductance really means.

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⚙️ What is an Inductor?

An inductor is a passive electronic component that stores electrical energy in the form of a magnetic field.
It mainly opposes changes in current — just like a capacitor opposes changes in voltage.

Whenever current starts flowing through an inductor, it generates a magnetic field around it.
And when that current changes (increases or decreases), the magnetic field changes too — which in turn induces a voltage that tries to oppose that change.

That’s the fundamental nature of an inductor.

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🧱 Structure — How It’s Made

An inductor is typically made of:

1. A coil of wire — usually copper, wound in loops or turns.

2. A core — which can be air, iron, or ferrite placed inside the coil to enhance its magnetic properties.

3. Two terminals / leads — for connection to the circuit.

The more turns the coil has, and the better the core material, the stronger the magnetic field it can create — and hence, the higher the inductance.

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⚙️ How Does an Inductor Work?

Before any current flows:

• There is no magnetic field around the coil.

When a voltage source is connected:

1. Current starts flowing through the wire coil.

2. As current flows, a magnetic field forms around the coil (according to Ampere’s Law).

3. If the current keeps increasing, the magnetic field grows — but this change in magnetic flux induces an opposing voltage (back EMF) in the coil (as per Faraday’s Law of Electromagnetic Induction).

4. This induced voltage always acts in the opposite direction of the applied voltage — this is Lenz’s Law in action.

So what’s happening inside is that the inductor resists any change in current.

• If you try to increase current, it generates a voltage that opposes the increase.

• If you try to decrease current, it generates a voltage that tries to keep it flowing.

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💡 In Simple Words

• Capacitor → opposes change in voltage

• Inductor → opposes change in current

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🔋 Energy Storage in an Inductor

An inductor stores energy in the magnetic field created by the current flowing through it.

The moment you disconnect the source, this magnetic field collapses and releases energy back into the circuit.

The energy stored is given by:

E = ½ L I²

where:

• E = energy stored (joules)

• L = inductance (henries, H)

• I = current through the inductor (amperes)

Just like a capacitor stores energy in an electric field, an inductor stores it in a magnetic field.

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🧮 What is Inductance?

Inductance is the ability of an inductor to store magnetic flux per unit current.

In simple terms, it tells how much magnetic field (or magnetic flux) an inductor can produce for a given current flowing through it.

It is denoted by L and measured in Henries (H).

Mathematically:

L = NΦ / I

where:

• N = number of turns in the coil

• Φ = magnetic flux linked with the coil (Weber)

• I = current through the coil (amperes)

It basically tells us how much magnetic flux is produced for a given current.

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⚡ Voltage–Current Relationship

The voltage across an inductor is given by:

V = L (dI/dt)

This means:

• If the current changes rapidly, the induced voltage is large.

• If the current is steady, dI/dt = 0, so the voltage across the inductor is zero.

Once fully energized with DC, an inductor behaves like a short circuit.

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🧠 Factors Affecting Inductance

1. Number of Turns (N): More turns → higher inductance

2. Core Material: Iron or ferrite cores concentrate magnetic flux → higher inductance

3. Cross-sectional Area (A): Larger area → stronger field → higher inductance

4. Length of Coil (l): Longer coil → weaker field → lower inductance

For a solenoid:

L = (μ N² A) / l

where:

• μ = permeability of the core material

• N = number of turns

• A = cross-sectional area

• l = length of the coil

Here, μ (mu) plays a similar role as ε (epsilon) in capacitors — it tells how well the core supports the magnetic field.

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🧩 Summary Table

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🔚 Conclusion

An inductor is a fundamental passive component that stores energy in the form of a magnetic field and resists changes in current. By generating an opposing voltage whenever current changes, inductors play a critical role in controlling current flow in electronic circuits.

Inductance defines how effectively an inductor can store magnetic energy, and it depends on physical factors like the number of turns, core material, and coil geometry. Inductors are widely used in filters, power supplies, energy storage systems, and signal processing circuits.

Understanding inductors and inductance provides a strong foundation for learning AC circuits, RL circuits, transformers, and advanced analog electronics.