🎓 Prepared by students from Boğaziçi University

What is an Inductor?

An inductor is a passive component — usually a coiled wire — that stores energy in a magnetic field when current flows through it and opposes any change in that current. Inductors are essential in transformers, filters, and power supplies.

Short answer

An inductor's induced voltage is proportional to the rate of change of current through it: V = L(di/dt), where L is inductance in henries (H).

Current Build-up in an RL Circuit

x: time (ms) · y: current (A)

Try it: interactive calculator

Induced voltage V

= 1*5/1

Inductance L1 HChange in current Δi5 ATime interval Δt1 s

Step-by-step worked examples

An inductor with L = 2H has its current change from 3A to 7A in 0.5s. Find the induced voltage.

Δi = 7 − 3 = 4 A
Δt = 0.5 s
V = L × (Δi/Δt) = 2 × (4/0.5) = 16 V

A 500 mH inductor experiences di/dt = 10 A/s. Find the induced voltage.

L = 500 mH = 0.5 H
V = L × (di/dt) = 0.5 × 10 = 5 V

Find the energy stored in a 4H inductor carrying 3A.

E = 0.5 × L × I²
E = 0.5 × 4 × 3²
E = 0.5 × 4 × 9 = 18 J

Flashcards

Quick quiz

Q1.An inductor with L = 3H has di/dt = 2 A/s. What is the induced voltage?

Correct answer: A. V = L × (di/dt) = 3 × 2 = 6 V.

Q2.What is the unit of inductance?

Correct answer: B. Inductance is measured in henries (H).

Q3.What is the formula for energy stored in an inductor?

Correct answer: B. Energy stored is E = 0.5 × L × I².

Q4.What law explains an inductor's opposition to a change in current?

Correct answer: C. Lenz's law says the induced EMF opposes the change that produced it.

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Common mistakes

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Thinking inductor voltage depends on the current's magnitude. — Correct: It depends on the rate of change of current (di/dt), not the current itself — steady current produces zero voltage.

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Confusing inductance with resistance. — Correct: Inductance opposes changes in current via a magnetic field; resistance opposes current flow by dissipating energy as heat.

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Believing inductors block DC in steady state. — Correct: In steady-state DC, di/dt = 0 so the voltage is zero — an ideal inductor acts like a short circuit (plain wire).

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Ignoring unit prefixes (H vs mH vs µH). — Correct: Convert to henries before calculating induced voltage.

FAQ

What is an inductor?

A coil that stores energy in a magnetic field and opposes changes in the current flowing through it.

What is the formula for an inductor?

V = L(di/dt) — the induced voltage equals inductance times the rate of change of current.

What are examples of inductors?

Transformers, chokes in power supplies, motor windings, and RF filters.

How do you calculate inductor voltage?

Multiply the inductance (L) by the rate of change of current (di/dt): V = L × (di/dt).