CEA - Energy · onds), 3,600 x1,500 J=5,400,000 J of elec - trical energy is transformed into thermal energy. This example shows that the joule is really too small a unit of energy

> INTRODUCTION

From natural sources to production challenges 4 > EnergyFrom natural sources to production challenges 4> Energy

FROM RESEARCH

TO INDUSTRY

> From natural sources to production challenges

WHAT IS ENERGY?THE DIFFERENT FORMS OF ENERGYCHARACTERISTICS OF THE DIFFERENTFORMS OF ENERGY

THE COLLECTION

1 > The atom2 > Radioactivity3 > Radiation and man4 > Energy5 > Nuclear energy: fusion and fission6 > How a nuclear reactor works7 > The nuclear fuel cycle8 > Microelectronics9 > The laser: a concentrate of light10 > Medical imaging11 > Nuclear astrophysics12 > Hydrogen

© Commissariat à l’Énergie Atomique et aux Energies Alternatives, 2005Communication DivisionBâtiment Siège - 91191 Gif-sur-Yvette cedexwww.cea.fr

ISSN 1637-5408.

4 >Energy

> INTRODUCTION

From natural sources to production challenges 4> Energy

> CONTENTS 32

introductionHuman beings have always needed energyto feed themselves and move about.Energy can be found in various forms. Today’s technologies are capable of tapping all pos-sible resources (e.g. fossil fuels, water, wind,sun) to produce large quantities of energy. Now,at the start of the 21st century, energy remains

“Energy is essential for mankind. It represents a major political,economic, scientific and environmentalchallenge.”

a major political, economic, scientific and envi-ronmental challenge. Of the many propertiesfound in material objects, energy is not onlyone of the most important but also one of themost abstract, since it is not actually tangible.

WHAT IS ENERGY? 4Different levels of energy 5Energy can change 5Energy can never be destroyed 6Energy can be measured 6Power 7

THE DIFFERENT FORMS OF ENERGY 8Kinetic energy 9Gravitational energy 9Elastic energy 9Work 9Thermal energy 10Electrical energy 10Radiation energy 10Chemical energy 10Nuclear energy 11

CHARACTERISTICS OF THE DIFFERENT FORMS OF ENERGY 12Diluted and concentratedenergy 13Degradation 15Storage 16Transporting energy 17Reserves 17Hazards 18

> INTRODUCTION 3

Energy

The wind is one of many sources of energy.

Energy can beobserved inmovement,chemical reactions,radiation, heatrelease, electricalsystems and atomicfission.


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> WHAT IS ENERGY? 54

DIFFERENT LEVELS OF ENERGYThe existence of energy can appear under different guises, depending on the situation.The faster a car is traveling, the more energyit has; but it carries less energy than a trucktraveling at the same speed. When a springis compressed, it has more energy than whenit is released. A battery has more energybefore it is used than when it has been dis-charged. The energy in a saucepan of waterincreases when it is heated.Thus energy appears in very different forms.For each of them, comparisons show how theamount of energy in a physical system dependson the state of that system. In the above examples, this state is characterized by thespeed and mass of the vehicle, the shape ofthe spring, or the charge of the battery. As wewill see, different types of energy can, at leastin part, take many other forms. These energytransformations are used in everyday life, butthey all generate losses.

ENERGY CAN CHANGEEnergy can be transmitted from one system toanother: it is transferred as heat from a radiatorto the air in a room. It can also change to takeon a different form. In a mechanical toy, thespring unwinds causing movement. The energyassociated with the movement of your bicycleis converted into heat in the brake blocks andwheel rims when you brake. The energy storedin a flashlight battery is transformed into electrical energy when you close the circuit.


This in turn is converted into light and ther-mal energy in the bulb. In a thermal power sta-tion, the energy stored in the fuel (chemicalenergy in coal and oil or nuclear energy in ura-nium) is transformed (by combustion ornuclear reaction) into heat; part of this heat isthen recovered in turbines as mechanicalenergy; finally, this mechanical energy is con-verted into electrical energy in the alternators.We perceive energy through these transfor-mations and transfers.

In a bulb, electrical energy is converted into light andthermal energy.

AN ABSTRACT CONCEPT, ENERGY COMESFROM THE GREEK WORD “ENERGIA”, MEANING“STRENGTH IN ACTION”.

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What is energy?

When a power station – here the EDF power station at Penly(Seine-Maritime) – “produces” electricity, it is reallytransforming nuclear energy into electrical energy.

From natural sources to production challenges 4> EnergyFrom natural sources to production challenges 4> Energy

> WHAT IS ENERGY? 76 > WHAT IS ENERGY?

ENERGY CAN NEVER BEDESTROYEDThe most remarkable characteristic of energyis that it can never be destroyed. When it istransferred from one system to another, orwhen it changes nature, no energy is createdor destroyed. If an object loses energy, thesame amount of energy must have beengained by another object linked to the first.Similarly, when energy changes form, theamount remains exactly the same.Therefore, terms such as “energy produc-tion” or “energy loss” used by journalists,economists and politicians are in fact inac-curate, because energy can be neither cre-ated nor lost. In a thermal power station,energy is not “produced”; rather, chemicalor nuclear energy is transformed into elec-trical or thermal energy. The overall amountof this conversion is described as the effi-ciency. The efficiency of a power station is33%, which means that for every 33 units ofelectrical energy sent over the electricity grid,100 units of nuclear energy were consumedand 67 units of heat produced.This heat, which is released into the environ-ment, for example as steam from coolingtowers, is generally lost. However, some powerstations recover some of it to heat homes orgreenhouses.We will see later that, although energy can neverbe destroyed, its different forms are not actu-ally equivalent, because not all the transfor-mations we can imagine are possible.

Before heat was recognized as a form of energy,the study of thermal exchanges had led to theintroduction of a unit of heat, the calorie,defined as the quantity of heat needed to raisethe temperature of one gram of water by onedegree Celsius. Experience has shown thattransforming mechanical energy into heat, andthe reverse, always gives the same ratio, i.e.1 calorie to 4.18 joules. These two forms ofenergy (mechanical energy and heat) are there-fore equivalent. For this reason, the caloriewas abandoned and heat and all other formsof energy are now measured in joules.

POWEREnergy exchange is characterized not only bythe amount of energy transferred or trans-formed, but also by the duration of the process.The concept of power is thus defined as theamount of energy exchanged per unit time. Theunit of power, the watt, is therefore the jouleper second. Therefore, in one hour (3,600 sec-onds), 3,600 x 1,500 J = 5,400,000 J of elec-trical energy is transformed into thermal energy.This example shows that the joule is really toosmall a unit of energy for everyday use. Inpractice we often use the kilowatt-hour (kWh),the amount of energy used by a device ratedat 1,000 W in one hour. One kWh is thusequivalent to 3,600 x 1,000 J = 3,600,000 J.In one hour, the electric heater used in theexample above, consumes 1.5 kWh andobviously radiates 1.5 kWh of thermal energyin the same period.

The average annual consumption of electricityper capita in France is more than 7,000 kWh,in the US it is twice that at 14,000 kWh andin Africa it barely exceeds 500 kWh. Nuclearpower plants account for three quarters of theelectricity produced in France; the remainingquarter is split between hydroelectric andthermal (coal and oil). But this electricity represents less than half our total energy consumption. The rest comes from the directuse of oil (gasoline and fuel oil), gas and coal.One third of our consumption is used forheating, and one quarter for transport.

ENERGY CAN BE MEASUREDAs energy cannot be destroyed, its differentforms can be measured using a single unit.The kinetic energy associated with the move-ment of an object of mass m and velocity v isequal to E = 1/2 mv2. When this mass isexpressed in kilograms and the velocity inmeters per second, this formula gives energyin joules (J), a legal unit in the InternationalSystem of Units (SI).

“Energy can never be destroyed: none of it can be lost and none created. This is the primary principle of thermodynamics.”

“An American consumes on averageabout twice theamount of electricity a French person consumes, who in turn consumes fourteentimes more electricitythan an African.”

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> THE DIFFERENT FORMS OF ENERGY


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KINETIC ENERGYKinetic energy is the energy associated with themovement of an object. We know that energyis proportional to the mass m and the squareof the velocity v of an object (provided that thevelocity is well below the speed of light, i.e.300,000 km/s).

GRAVITATIONAL ENERGYTwo massive bodies attract each other. Thisphenomenon, known as gravitational force, isweak for small objects but becomes very strongfor stars and planets. The Sun and the Earth,and the Earth and Moon, attract each other;gravity is the gravitational force exerted by theEarth on objects in its vicinity. Gravitationalenergy corresponds to this force and is greater

The differentforms of energy

Dams offer the advantage of being both sources andreservoirs of energy.

when bodies are farther away from each otherthan when they are close together. Gravita-tional energy is called potential energy becauseit is only perceptible when converted intoanother form of energy. The potential energy ofan elevator car is greater on the sixth floor thanon the ground floor because on the sixth floorit is farther away from the center of the Earth,which attracts it. If you cut the cable andreleased the safety brakes, the car would fall,accelerating all the time, and its potentialenergy would change into more visible kineticenergy. Similarly the energy of a 1 kg mass ofwater on the surface of a lake behind a dam isgreater than its energy when it is at the foot ofthe dam. For a difference in altitude of 100 m,its difference in potential energy is 981 J. It isthis energy that is exploited in a hydroelectricpower station, where the falling water turns theturbines that drive the alternators.

ELASTIC ENERGYThis is another type of potential energy, in thiscase associated with the deformation of elas-tic objects, e.g. the tension in a spring or the compression of a gas.

WORKThis term refers to the transfer of energy thatoccurs when a force is applied to an object andthe point of application of the force moves.When a weight is lifted or when water is raisedfrom the bottom of a dam to the top, work isdone, enabling the object in question to acquire

ENERGY CAN BE OBSERVED IN MOVEMENT,CHEMICAL REACTIONS, RADIATION, HEAT RELEASE,ELECTRICAL SYSTEMS AND ATOMIC FISSION.

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The different forms of energy

nuclei provide nuclear energy. As they trans-form the structure of atomic nuclei, nuclearreactions release heat. This is the mechanismat work within the Sun’s core, which producesthe heat radiated by the Sun through thefusion of hydrogen nuclei into helium nuclei.In our nuclear power plants, another nuclearreaction is used, namely the fission of uraniumnuclei, which splits each nucleus into two different nuclei approximately twice as small.Some of the heat produced (33%, as seen onpage 6) is converted into electricity.

> THE DIFFERENT FORMS OF ENERGY


> THE DIFFERENT FORMS OF ENERGY 1110

A radiator conveys its heat to us not onlythrough the surrounding air, but also directlyas infrared radiation. In the filament of an elec-tric bulb, the electrical energy is transformedinto heat, and this heat is given off principallyas radiation energy, both visible light andinfrared. A microwave oven transfers heat tofood starting with electrical energy, which isconverted into “microwave” radiation, similarto that of a radar. Conversely part of the lightenergy from the Sun can be converted into elec-trical energy using photovoltaic cells. Radiowaves also carry energy, at a weak level but withsufficient strength to carry sound, images orinformation.

CHEMICAL ENERGYChemical energy is associated with the bondsof atoms inside molecules. It is greater whenthese atoms are separated than when they arebound as molecules, and the greater the bind-ing energy, the greater the difference in mass.Chemical reactions change the chemicalenergy of bodies and therefore often transformthis energy into other forms of energy, usuallyheat. A gas fire produces a certain amount ofthermal energy, equal to the difference betweenthe chemical energy of the gas and oxygen consumed, and that of the combustion prod-ucts (steam and carbon dioxide). In a coal- oroil-fired power station, only a fraction of theheat from combustion is converted into elec-trical energy. In an accumulator or electric bat-tery, part of the chemical energy released bythe reaction is directly recovered as electricity.

greater potential energy. The work done on apump compressing a gas increases the elasticenergy of that gas and heats it.The forms of energy described so far are mechanical energies.

THERMAL ENERGYOn an atomic scale, heat appears as the disor-dered, fairly rapid movement of molecules. Aswe perceive it, it is the form of energy involvedin temperature variations or when materialschange state (e. g. when ice melts or waterevaporates). It can be transferred between twoobjects without changing into another form ofenergy (thermal conduction). It can also be con-verted into mechanical energy, in a turbine, asteam engine or a jet engine, although this con-version can only be partial, as shown later.

ELECTRICAL ENERGYCharged particles exert electrical forces oneach other. Just as gravitational potentialenergy is associated with gravitational forcesor gravity, electrical potential energy is asso-ciated with the electrical forces betweencharges. When these move around a circuit,fairly rapid transfers of energy take place,measured by electric power. Electrical energycan be transformed into heat in a resistor (e.g.a heater), or into work in a motor.

RADIATION ENERGYRadiation carries energy, even across a vacuum.The Sun transmits about 1 kW per square meterof power as visible light and infrared radiation.

Although they seem different, thermal, elec-trical, radiation and chemical energy actuallyall have the same source: on a microscopicscale, they are all connected to the electricalforces between charged particles.

NUCLEAR ENERGYNuclear energy is located in atomic nuclei.These nuclei, which are 100,000 timessmaller than the atoms, are made up of more,very tightly bound, fundamental particles,called protons and neutrons. Just as the bondsbetween atoms to form molecules are a sourceof chemical energy, those created by nuclearforces between protons and neutrons to form

“Energy can change form. For example, oil combustion converts it into heat.”

Transformation of energy

Gasoline

Engine Movement Friction

Alternator

Battery Sparkplug

HeadlightLIGHT ENERGY

CHEMICALENERGY

HEATKINETICENERGY

MECHANICALENERGY

CHEMICALENERGY

HEAT FROMCOMBUSTION

Here, by way of example, are theenergy transformations produced in a car:

• The chemical energy of gasolineand air is transformed into heat bycombustion. This is transmitted, bythe production of hot gases, first tothe cylinders and then to the pistons.At this stage, it is transformed intomechanical energy and starts to movethe car, which acquires a certainamount of kinetic energy.

• The friction of the air against thebodywork and the wheels against theground transforms all this energy intoheat (on a flat road at a constantspeed).

• Some of the energy from the engineis converted into electrical energy,which drives an alternator. Thecurrent produced is used to make thespark plugs spark to light the fuel, and to recharge the battery, therebyincreasing its chemical energy. It isalso used to light the headlights toemit light energy. Thus, at a givenspeed, we consume slightly moregasoline by night than by day.

> CHARACTERISTICS OF THE DIFFERENT FORMS OF ENERGY


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Although energy is a single physical variable,its various forms have very different charac-teristics. In practice, the choice of energy useddepends on the intended purpose. For a par-ticular purpose, for example electrical energyproduction, it is essential to weigh up the prosand cons of each potential solution; there aremany selection criteria.

DILUTED AND CONCENTRATEDENERGYJust as a $50 bill is worth the same asfifty $1 bills, some forms of energy are con-centrated in a much smaller volume than oth-ers. In this respect, there are three categoriescorresponding to the three types of force seenearlier.

Gravitational energyThe amount of gravitational energy availableis only significant if huge masses are involved.It was demonstrated earlier that 1 kg of water falling from a height of 100 m onlyrepresents 981 J of energy (see page 9) and 1 kWh is equivalent to 3,600,000 J (see page 7). To release only 1 kWh,3,600,000 J/981 J/kg, or 3.67 metric tonsof water, must be dropped 100 m. Hydro-electric power stations are therefore not veryefficient in this respect. The mechanical ener-gies at work in our everyday life are also ona very small scale. The kinetic energy of acar weighing 1 metric ton traveling at100 km/h is only 0.1 kWh.

Thermal, electrical, radiationand chemical energyThe middle category features thermal, elec-trical, radiation and chemical energy, whichfor everyday use can be measured in kWh perkg of matter. It takes 0.1 kWh to melt 1 kg ofice, or 0.7 kWh to evaporate 1 kg of water at 100°C. Domestic appliances consumebetween 0.1 and 5 kW of electrical power. Thecombustion of 1 kg of oil or gas provides

Characteristics ofthe different formsof energy

POWER, “LOSS” AS HEAT, CAPACITY FORRENEWAL… THESE ARE THE CHARACTERISTICS THATDETERMINE HOW WE USE DIFFERENT ENERGIES.

The middle category, between the diluted andconcentrated energies, includes thermal,electrical, radiation and chemical energy.

Example: oil or gas combustion.

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approximately 12 kWh. We human beingsmake biochemical energy from the food we eatand the air we breathe. We use this energy tomaintain our body temperature at 37°C andengage in activity; the corresponding powerwe use is 100 W at rest and 500 W duringphysical activity.The difference between these first two cate-gories can be illustrated as follows: if themechanical energy of an egg dropped from thetop of the Eiffel tower were entirely transformedinto heat and used to heat the egg, its tem-perature would only increase by 0.7°C.

Nuclear energyNuclear energy is a far more concentrated formof energy. One kilogram of natural uraniumprovides 100,000 kWh of heat in today’snuclear power plants, while burning 1 kg of

coal supplies only8 kWh. That is whywe handle only

fairly small masses of nuclear fuel in elec-tricity production. A nuclear power plant witha power rating of 1,000 MW (109 W) uses27 metric tons of enriched uranium per year,a quarter of its loading, while a thermal powerstation with the same power rating burns1,500,000 metric tons of oil per year. In fact,we can only extract by industrial means a verysmall proportion of the nuclear energy storedin matter. Nuclear reactions in the Sun trans-form hydrogen into helium. In this way, 1 kgof hydrogen generates 180 million kWh.

> CHARACTERISTICS OF THE DIFFERENT FORMS OF ENERGY 1514

Nuclear energy is one of the mostconcentrated forms of energy.

DEGRADATIONExperiments have shown that a physical sys-tem naturally tends to become spontaneouslymore and more disordered. Among the differ-ent forms of energy, heat corresponds to thechaotic movement of molecules. The otherforms of energy, sometimes described as the“noble” or “available” forms, are ordered atthe microscopic level and thus tend to changeinto heat. This phenomenon is known as dis-sipation, and we say that heat is a degradedform of energy.It is easy to produce heat from an equivalentamount of a noble energy, for example in elec-tric or combustion boilers and ovens, or in solarcollectors for water heaters. However, thereverse transformations are impossible. A givenamount of heat cannot be totally convertedinto mechanical, electrical or chemical energyusing a closed-cycle apparatus, returning

periodically to its initial state. This impossi-bility is one of the fundamental laws of physics, confirmed by countless experiments: natureallows us to convert only a fraction of the heatavailable into another form of energy, and thisfraction can never exceed a certain maximumvalue. This limits the efficiency of steam tur-bines in power stations, car and airplaneengines, and all other machines generatingmechanical energy from the thermal energy ofa hot gas.Heat often appears as a “loss”, when otherforms of energy are handled (except of course,for domestic or industrial heating). In orderto exploit nuclear energy or chemical energyin a power station or a car, we use a nuclearor chemical reaction to generate heat, onlysome of which can then be converted backinto electrical or mechanical energy. The bestsituation is the direct conversion of mechanicalenergy into electrical energy, and vice versa.But even in these cases, it is difficult inpractice to prevent part of these noble energiesfrom turning into heat. If the shaft of anelectric motor is driving the shaft of analternator, the motor is converting electrical

Most French nuclear power plantsare equipped with pressurized waterreactors (PWRs).

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CALCULATING TOTAL ENERGYIn the Sun, 1 kg of hydrogen produces 180 million kWh. These high energy levels areupheld by Einstein's famous equation E = mc2, whichstates that the total energy of a body is proportionalto its mass, a new equivalence; but the conversionfactor is enormous because the speed of light, c, is300,000 km/s. This means that a mass of only 1 mgis equivalent to 25,000 kWh. In a nuclear powerplant, the transformation of 1 kg of natural uraniuminto other elements reduces the nuclear energy of the fuel by 100,000 kWh, and therefore its massby 4 mg.



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> CHARACTERISTICS OF THE DIFFERENT FORMS OF ENERGY16

energy into mechanical energy, and thealternator is converting this back into electricalenergy. But overall, less energy is recoveredthan was initially supplied; the difference isaccounted for by a release of heat through thejoule heating in the coils, or through frictionin the bearings, and this is impossible toeliminate totally.The equivalence between energies can becompared to the equivalence between convertible currencies, with 1 dollar worth0.98 euro for example. Dissipation as heatplays the same role as bank commissioncharges, which prevent us from recoveringthe amount we started with if we change dollars into euros and back. The same overallvalue or energy still exists, but not in ourpockets.

STORAGEIt is difficult to store energy in any sizeablequantity except in certain forms. Storing andrecovering it involve conversions, and there-fore dissipation. Electrical energy can bestored in accumulators as chemical energy.But discharging an accumulator provides lesselectrical energy than it was charged with,because the electrochemical reactions thatoccur involve quite significant heat degrada-tion. Moreover, accumulators are costly andheavy because they can only store 0.1 kWhper kg, which, along with price, has been theprincipal obstruction to the development ofan electric car.

RESERVESEnergy sources can be divided into fossil ener-gies and renewable energies. The first rely onthe use of minerals and fuels formed through-out the Earth’s history and only exist in limitedquantities. Considering rising consumption and

Study of thermal exchanges by simulation.

The battery: a method of storing electricalenergy as chemical energy.

Our electrical power consumption variesthroughout the day, rising sharply, for example,in the evening. It is hard for nuclear powerplants to keep up with these variations. Becauseof low energy loss in electromechanicalexchanges, dams are used not only as sourcesof hydroelectric energy, but also as reservoirsof energy. At off-peak times, water is pumpedup from the bottom of the dam using elec-tricity from nuclear power plants, and at peaktimes this water is let down again, operatingthe power station’s turbines and generatingelectricity. Because this form of storage usesmechanical energy at one stage, it requiresthe movement of very large masses of water –several metric tons per kWh stored.Chemical and nuclear fuels store energyefficiently, but we can only recover such energyas heat.

TRANSPORTING ENERGYThe relative ease of storage and also of trans-portation over long distances of coal, oil andgas has been one of the key factors of indus-trial development over the last two centuries.The increasing use of the car is also due to itsability to carry enough fuel to travel severalhundred kilometers. However, electricity is theonly form of energy that can be convertedalmost entirely into any of the others andtransported over long distances in large quan-tities at relatively low cost. Nevertheless,energy losses due to heat from high voltagelines and transformers reach 8%.

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> CHARACTERISTICS OF THE DIFFERENT FORMS OF ENERGY18

the possible discovery of new deposits, esti-mated global reserves stand at a few decadesfor oil, about a hundred years for gas and ura-nium, and a few centuries for coal. The devel-opment of technologies such as breeder reac-tors, however, would multiply our nuclearenergy reserves more than a hundredfold.

Renewable energiesRenewable energies reach us directly or indi-rectly from the Sun through the constant radi-ation it emits. They include solar, water andwind energy, and also the chemical energy built

up in plant life, which can be used for fuel(timber, waste, alcohol). However, the totalamount of power drawn from these renewableenergies is limited. Forests should not be burntmore quickly than they can grow. Althoughrenewable energies constitute a useful top-up,they can only replace a small proportion of fossilenergies.

HAZARDSHandling all types of energy has, to somedegree, harmful effects on our environment,and these must be individually assessed.

Certain combustion residues of coal, oil, gaso-line or even gas if it does not burn properly,are harmful to human health. Carbon dioxideis the gas emitted in the greatest quantity. Itbuilds up in the atmosphere and is in dangerof affecting our climate by increasing thegreenhouse effect. Nuclear reactions generateradioactive waste, which must be processedor reduced, especially long-lived waste. Hydro-electric power stations have a negative impacton valleys. Wind turbines are noisy and do notguarantee continuous production. They alsotake up a great deal of space for the rathersmall amount of power they provide. Photo-voltaic cells have the same drawback and arevery expensive. The conversion of solar energyinto electricity is therefore only suitable forsupplying very isolated dwellings, or for oper-ating small portable devices such as pocketcalculators. Furthermore, a lot of energy isrequired to manufacture photovoltaic cells.

Thermal pollutionThermal pollution is the consequence of energydegradation and all non-renewable energysources. Most fossil energies used are even-tually converted into heat. An earlier exampledemonstrated how a car operates by convertingchemical energy supplied as gasoline into heatreleased into the environment. Even thoughthis thermal pollution is too slight to influencethe climate, it can have local effects: a thermalor nuclear power plant cooled by water from ariver increases the downstream temperature

of this water significantly, and can thus modifyits ecological balance. Significant savings canbe made by recovering this lost heat. Half theenergy we consume is intended for domesticor industrial heating, making use of coal, gas,fuel oil or electricity. This could be reducedthrough more efficient use of the heat frompower stations. Average per capita energy con-sumption reflects not only standards of living,but also the amount of energy wasted. Thisexample illustrates a key point: the manysources of energy reflect the diversity of uses,and a global approach to energy problems isessential.

“Renewable energiesare those that reach us directly orindirectly from theSun, the wind, etc.”

Wind turbines exploit a renewable source of energy but only produce a small amount of power.

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CEA - Energy · onds), 3,600 x1,500 J=5,400,000 J of elec - trical energy is transformed into thermal energy. This example shows that the joule is really too small a unit of energy