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Courses/Electrical Fundamentals/Capacitors & Inductors

lesson · 9min · Lesson 29 of 37

Capacitor construction and capacitance

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

Capacitor construction and capacitance

Electrical Fundamentals · Lesson 29 · Beginner

BeginnerReview: professional review pending

Purpose

Relate capacitor construction, charge storage, geometry, voltage rating, and stored energy.

Before you beginCharge · Voltage · Electric field

Learning objectives

  • Define capacitance
  • Use Q=CV
  • Predict geometry effects
  • Calculate stored energy

A capacitor separates charge on conductors divided by a dielectric; it stores energy in the electric field rather than creating charge.

CAPACITOR ENERGYCAPACITOR ENERGY E = ½CV²stored energy and time-dependent response

Core theory

Capacitance is charge per potential difference. Larger plate area and permittivity increase capacitance; larger spacing reduces it.

Real capacitors have voltage, polarity, temperature, ripple-current, leakage, and tolerance limits.

Stored energy is ½CV², so voltage has a squared effect.

Terms, symbols, and units
TermMeaningSymbolUnit
CapacitanceCharge stored per voltCfarad (F)
DielectricInsulating material between electrodesNot applicableNot applicable
Stored energyEnergy in electric fieldEJ
Q=CV; E=½CV²

Use farads, volts, coulombs, and joules.

C, F, V, J
Worked exampleA 1000 µF capacitor is charged to 24 V. Find charge and energy.

Assumptions: Capacitance is 0.001 F.

  1. Charge: Q=0.001×24=0.024 C.
  2. Energy: E=0.5×0.001×24²=0.288 J.
  3. Check: Doubling voltage would quadruple energy.

Q=24 mC and E=0.288 J.

Reasonableness check: The unit path gives coulombs and joules.

Common mistakes
  • Leaving µF unconverted
  • Assuming voltage rating is operating voltage
  • Ignoring polarity on electrolytics

Where this appears in practice

Capacitors filter supplies, start motors, couple signals, correct power factor, and store pulse energy.

SafetyCapacitors can retain hazardous voltage after isolation. Use a rated discharge method, verify voltage, and never short large capacitors casually.
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

If voltage doubles at fixed capacitance, stored energy changes by what factor?

Four. Energy depends on voltage squared.

Answer: Four. Energy depends on voltage squared.

Practical exercise

Calculate charge and energy for 47 µF at 12 V, showing prefix conversion.

Summary

  • Capacitance is charge per volt
  • Geometry and dielectric matter
  • Stored energy scales with V²

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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