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Courses/Electrical Fundamentals/Capacitors & Inductors

lesson · 9min · Lesson 31 of 37

Inductor construction and inductance

Course syllabusCourse overview
01Atoms, Electrons & Electric Charge
  1. ReadWhat is electricity?: atomic model
  2. ReadElectric charge and the coulomb
  3. ReadConductors, insulators, and semiconductors
  4. ReadConventional current vs electron flow
  5. quizModule quiz
02Voltage, Current & Resistance
  1. ReadPotential difference: the driving force
  2. ReadCurrent: the rate of charge flow
  3. ReadResistance and resistivity
  4. ReadOhm's Law: derivation and examples
  5. exerciseWorked examples: Ohm's Law problems
03Series & Parallel Circuits
  1. ReadSeries circuits: characteristics and rules
  2. ReadParallel circuits: characteristics and rules
  3. ReadCombined series-parallel networks
  4. ReadVoltage dividers and current dividers
  5. exerciseCircuit analysis practice
04Kirchhoff's Laws
  1. ReadKCL: Kirchhoff's Current Law
  2. ReadKVL: Kirchhoff's Voltage Law
  3. ReadMesh and nodal analysis
  4. exerciseKirchhoff's law problems set
05Power & Energy
  1. ReadElectrical power: watts and horsepower
  2. ReadEnergy: kilowatt-hours and joules
  3. ReadEfficiency and power loss in cables
  4. quizPower quiz
06Alternating Current Fundamentals
  1. ReadAC vs DC: why AC won
  2. ReadSinusoidal waveforms: peak, RMS, average
  3. ReadFrequency and period
  4. ReadPhase relationships
  5. ReadAC circuit analysis introduction
07Capacitors & Inductors
  1. ReadCapacitor construction and capacitance
  2. ReadCapacitors in AC circuits: reactance
  3. ReadInductor construction and inductance
  4. ReadInductors in AC circuits: reactance
  5. ReadRC and RL circuits: time constants
08Measurement & Instruments
  1. ReadMultimeters: AC/DC voltage and current
  2. ReadClamp meters and measuring live current
  3. ReadOscilloscopes: reading waveforms
  4. quizFinal assessment
Lesson · 9min
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In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Inductor construction and inductance

Electrical Fundamentals · Lesson 31 · Beginner

BeginnerReview: professional review pending

Purpose

Relate inductor construction, flux linkage, changing current, and stored magnetic energy.

Before you beginCurrent · Magnetic field · Rate of change

Learning objectives

  • Define inductance
  • Use v=L di/dt
  • Predict core and turns effects
  • Calculate stored energy

An inductor produces voltage when its current changes and stores energy in its magnetic field.

INDUCTOR ENERGYINDUCTOR ENERGY E = ½LI²stored energy and time-dependent response

Core theory

Inductance links current change to induced voltage. More turns and suitable core permeability generally increase inductance.

An ideal inductor passes steady DC after transients but opposes rapid current change.

Real windings have resistance, core loss, capacitance, saturation, and thermal limits.

Terms, symbols, and units
TermMeaningSymbolUnit
InductanceFlux-linkage response to currentLhenry (H)
Back emfInduced voltage opposing current changeNot applicableNot applicable
SaturationCore region where flux no longer rises proportionallyNot applicableNot applicable
v=L·di/dt; E=½LI²

Polarity follows the chosen passive sign convention.

V, H, A/s, J
Worked exampleA 0.20 H ideal inductor carries 3 A. Find stored energy.

Assumptions: Linear unsaturated inductance.

  1. Square: I²=9 A².
  2. Substitute: E=0.5×0.20×9.
  3. Calculate: E=0.90 J.

Stored magnetic energy is 0.90 J.

Reasonableness check: Energy is positive and scales with current squared.

Common mistakes
  • Assuming zero winding resistance
  • Treating inductance as constant through saturation
  • Opening an energized coil without considering induced voltage

Where this appears in practice

Inductors appear in relays, contactors, motors, transformers, filters, and converters.

SafetyInterrupting inductive current can create a high voltage and arc. Use suitable suppression, isolation, and discharge controls.
Local code checkThe component relationships are universal. Product ratings, discharge provisions, protective measures, permitted work, and test procedures must follow current local rules and manufacturer data.

Knowledge check

What physical quantity can an ideal inductor current not change instantaneously?

Current. Instantaneous current change would require unbounded voltage.

Answer: Current. Instantaneous current change would require unbounded voltage.

Practical exercise

Calculate energy in 50 mH at 2 A and predict the effect of doubling current.

Summary

  • Inductors oppose current change
  • Energy is magnetic
  • Real cores and windings have limits

Sources and review

  • University Physics Volume 2: Capacitance, Inductance, and AC Circuits: OpenStax; Current web edition; Physics reference
  • The International System of Units (SI Brochure): BIPM; 9th edition, updated 2026; International

Editorial review date: 2026-08-21. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

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