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Educational use: ElectraCore supports learning and preliminary checks. It does not replace a competent electrician or engineer. Verify results, equipment data, and current local regulations before installation or live work.
Courses/Electrical Fundamentals/Voltage, Current & Resistance

lesson · 7min · Lesson 7 of 37

Current: the rate of charge flow

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 · 7min
SIMPLIFIED CHARGE MODEL · I = Q / t+electron drift = current1 A = 1 coulomb per second
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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

Current: the rate of charge flow

Electrical Fundamentals · Lesson 7 · Beginner

BeginnerReview: professional review pending

Purpose

Explain current as charge flow and calculate current, charge, or time with consistent units.

Before you beginElectric charge and the coulomb · Division and unit conversion

Learning objectives

  • Define the ampere
  • Use I = Q/t
  • Convert mA to A
  • Distinguish conventional current from electron drift

Current tells us how quickly charge crosses a chosen section of a circuit. A large current means more charge passes each second.

CURRENT: CHARGE PER SECONDCURRENT: CHARGE PER SECOND I = Q ÷ t3 C each second = 3 A

Core theory

One ampere means one coulomb passes a cross-section each second. Current is assigned a conventional direction from higher to lower potential in the external circuit.

In metallic conductors electrons drift in the opposite direction to conventional current. Circuit laws remain consistent when one convention is used throughout.

Current is measured by placing an ammeter in series so the same branch current passes through the instrument.

Terms, symbols, and units
TermMeaningSymbolUnit
CurrentRate of charge flowIampere (A)
ChargeElectrical quantity carried by particlesQcoulomb (C)
TimeDuration of the measured transfertsecond (s)
I = Q ÷ t

Divide charge passing the reference point by elapsed time.

A = C/s; 1000 mA = 1 A
Worked exampleA control circuit transfers 0.45 C in 150 ms. Find the average current.

Assumptions: Current is averaged across the 150 ms interval.

  1. Convert time: 150 ms = 0.150 s.
  2. Substitute: I = 0.45 C ÷ 0.150 s.
  3. Calculate: I = 3.0 C/s = 3.0 A.

The average current is 3.0 A.

Reasonableness check: At 3 C/s, 0.45 C takes 0.15 s to pass.

Common mistakes
  • Using milliseconds without converting to seconds
  • Connecting an ammeter across a supply
  • Confusing electron direction with conventional current

Where this appears in practice

Protective devices, conductor sizes, connectors, and switches are selected partly from the current they must carry.

SafetyAn ammeter has a low-resistance current path. Connecting it directly across a voltage source can cause high fault current, arc, burns, and equipment damage.
Local code checkPermitted measurement methods and test equipment ratings vary. Follow manufacturer instructions and current workplace/local electrical-safety requirements.

Knowledge check

How much charge passes at 250 mA for 8 s?

2 C. Convert 250 mA to 0.250 A, then Q = It = 0.250 × 8 = 2 C.

Answer: 2 C. Convert 250 mA to 0.250 A, then Q = It = 0.250 × 8 = 2 C.

Practical exercise

Calculate the charge moved by a 20 mA indicator during 30 s, then verify the unit path from A·s to C.

Summary

  • Current is charge per second
  • Convert prefixes before calculating
  • Ammeters are connected in series

Sources and review

  • The Feynman Lectures on Physics, Volume II: Caltech; Online edition; Physics reference
  • International Electrotechnical Vocabulary: Electromagnetism: IEC; Current edition must be confirmed; International

Editorial review date: 2026-08-14. 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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