LITTORAL CÔTE D’OPALE

ElectricityIntroduction

Mathieu Bardoux

IUT du Littoral Côte d’OpaleDépartement Génie Thermique et Énergie

First year

Summary

1 Electric current

2 Voltage and Power

3 Electrical Resistance

4 Hydraulic Analogy

Mathieu Bardoux (IUTLCO GTE) Electricity First year 2 / 20

Electric current

Summary

1 Electric currentElectron ?Electric current

2 Voltage and PowerVoltagePower

3 Electrical ResistanceDefinitionJoule effect

4 Hydraulic Analogy

Mathieu Bardoux (IUTLCO GTE) Electricity First year 3 / 20

Electric current Electron ?

Electron ?

I Elementary particle (light particle or lepton)I Negative electric charge : −e , with e = 1,602176535×10−19 CI Electrons + Protons (charge : e) + Neutrons = Atoms

Mathieu Bardoux (IUTLCO GTE) Electricity First year 4 / 20

Electric current Electron ?

Atoms : structure and dimensions

10−15 m

10−10 m

Mathieu Bardoux (IUTLCO GTE) Electricity First year 5 / 20

Electric current Electron ?

Conductors vs Insulators

Conductors : high conductivity / low resistivityI métals (copper, gold, aluminium, iron & alloys)I carbon (graphite, diamond, nanotubes. . . )I water (+ electrolytes)I human bodyI ground

Insulators : low conductivity / high resistivityI glassI porcelainI paperI dry woodI rubberI plastic

Mathieu Bardoux (IUTLCO GTE) Electricity First year 6 / 20

Electric current Electric current

Electric current

I overall flow of electric chargesI created by the action of electromagnetic forceI carriers : ions or (in most cases) electronsI in electrical networks, a generator produces a charge imbalance⇒ electrons move through a closed loop

Mathieu Bardoux (IUTLCO GTE) Electricity First year 7 / 20

Electric current Electric current

Current intensity

i =dqdt

By definition, 1A = 1C · s−1

The current is measured using an ammeter connected in series.

A

i

Mathieu Bardoux (IUTLCO GTE) Electricity First year 8 / 20

Electric current Electric current

Conventions

I Current can be created by positive or negative charge carriers.I Conventional current is arbitrarily defined as a positive charges

flow.I By convention, the electrical current exits the generator through

the positive (+) terminal and returns to the generator through itsnegative (-) terminal.

I Inside the generators, the inverse convention applies.I The conventional direction may differ from the actual direction of

the charge carriers.

Mathieu Bardoux (IUTLCO GTE) Electricity First year 9 / 20

Electric current Electric current

Propagation rate

I Propagation rate of the electric current in a copper wire :273000 km · s−1

I This is not the speed of electrons (a fraction of millimeter persecond)

I Signal is faster than matter

What distance does an electron travel in domestic network ?

Mathieu Bardoux (IUTLCO GTE) Electricity First year 10 / 20

Electric current Electric current

Propagation rate

I Propagation rate of the electric current in a copper wire :273000 km · s−1

I This is not the speed of electrons (a fraction of millimeter persecond)

I Signal is faster than matter

What distance does an electron travel in domestic network ?

Mathieu Bardoux (IUTLCO GTE) Electricity First year 10 / 20

Electric current Electric current

Effects

I HeatingI Chemical decompositionI Mechanical actionI Creation of magnetic fieldsI . . .

Mathieu Bardoux (IUTLCO GTE) Electricity First year 11 / 20

Voltage and Power

Summary

1 Electric currentElectron ?Electric current

2 Voltage and PowerVoltagePower

3 Electrical ResistanceDefinitionJoule effect

4 Hydraulic Analogy

Mathieu Bardoux (IUTLCO GTE) Electricity First year 12 / 20

Voltage and Power Voltage

Voltage

I Voltage between two points = work done per unit of chargeagainst a static electric field to move between these points.

I Voltage unit = VoltI 1V = 1J ·C−1

I Notation U (single-phase) or V (three-phase).I Measured with a voltmeter or an oscilloscope connected in

parallel.

V

R

−+U

Mathieu Bardoux (IUTLCO GTE) Electricity First year 13 / 20

Voltage and Power Power

Electrical power

I Power = Energy per unit of TimeI Power unit = WattI 1W = 1J · s−1 and 1J = 1W · sI Power = flow of EnergyI Electrical power : P = U · I

Mathieu Bardoux (IUTLCO GTE) Electricity First year 14 / 20

Electrical Resistance

Summary

1 Electric currentElectron ?Electric current

2 Voltage and PowerVoltagePower

3 Electrical ResistanceDefinitionJoule effect

4 Hydraulic Analogy

Mathieu Bardoux (IUTLCO GTE) Electricity First year 15 / 20

Electrical Resistance Definition

Electrical resistance

I Measurement of the difficulty to pass a current through acomponent

I Leads to a drop in carriers energy when passing through thecomponent

I Unit : OhmI Ohm’s law : U = R · I

Mathieu Bardoux (IUTLCO GTE) Electricity First year 16 / 20

Electrical Resistance Joule effect

Power dissipation in a resistor : Joule effect

I Conversion of electrical energy into heat.I P = U · II P = R · I 2

I P =U 2

R

Mathieu Bardoux (IUTLCO GTE) Electricity First year 17 / 20

Hydraulic Analogy

Summary

1 Electric currentElectron ?Electric current

2 Voltage and PowerVoltagePower

3 Electrical ResistanceDefinitionJoule effect

4 Hydraulic Analogy

Mathieu Bardoux (IUTLCO GTE) Electricity First year 18 / 20

Hydraulic Analogy

Hydraulic AnalogyExample of a waterfall

I Electrical charge⇔ Quantity of waterI Electrical current⇔ Hydraulic volume flow rateI Voltage⇔ Hydraulic head

BFluid particles can move at variable speed

Mathieu Bardoux (IUTLCO GTE) Electricity First year 19 / 20

Conclusion

ConclusionIn this chapter we have seen. . .

I how electric current is created in conductive materialsI the definitions of fundamental parameters of electric currentI the main properties of resistors

Mathieu Bardoux (IUTLCO GTE) Electricity First year 20 / 20