THErheckathorn.weebly.com/uploads/2/7/1/0/27107965/the_toaster.pdfobject, a voltmeter, an ammeter, a clock, a thermometer, hook-up wires and a source of electricity. 7. Given an object

THETOASTER

A MODULE ON HEAT AND

ENERGY TRANSFORMATIONS

PRINCIPAL AUTHOR: Bruce B. MarshSUNY-Albany

PROJECT DIRECTORS: Carl R. Stannard

Bruce B. Marsh

State University of New Yorkat Binghamton

In our technological society,there are many devices which useelectricity for heating processes.You are probably most familiarwith those which appear in thehome, such as irons, water heaters,clothes dryers, hair dryers, coffeemakers, ranges, and toasters. Al-though you may be less familiarwith them, devices based on thesame properties are common itemsin industrial manufacturing plantsand research laboratories.

This module introduces theprinciples needed to understandthe operation of such devices. Wehave chosen to use the toaster asan example. As you work throughthe module, you should try to reachthe following goals:

1. Learn about processes thatchange electrical energy intoheat.

2. Learn to ident ify the majorforms of energy and to de-scribe hm" one form changesinto another.

3. Discover that materials ex-

pand when heated and use aformula that describes thiseffect.

4. Learn to describe one or twosystems which are controlledby a thermal expansion device.

This list of goals should giveyou a general idea of the topics in-cluded in the module. Mor~ specificstatements on what you will be ex-pected to know and be able to do areprovided by the folloWing list oflearning objectives.

This list of objectives indi-cates what you should be able to doafter completing the study of thismodule:

1. Define in clear and precisesentences the following words:energy, power. specific heat.heat capacity, coefficient oflinear expansion.

2. Determine the power deliveredto a circuit by a battery byperforming the folloWing twosteps within 15 minutes:

a. Given a circuit diagram,a battery, hook-up wires,a resistor, an ammeter,and a voltmeter, measurethe appropriate voltageand current.

b. Calculate the power.3. Determine the energy delivered

to a resistor by performing thefollowing two steps within 20minutes.a. Given the same equipment

as for the preceding ob-'.jective plus a timer, meas-

ure the appropriate voltage,current and time interval.

b. Calculate the energy injoules.

4. Given two of the following threequantities for an object, deter-mine the third: heat capacity,temperature change, quantity ofheat.

5. Convert energies from anyoneto any other of the followingunits: joules, calories,B.t.u. IS, kilowatt-hours. (Atable of conversion factorswill be provided.)

6. Determine experimentally with-in 30 minutes the heat capacityof an object by measuring thetemperature rise for a measured

input of electrical energy usingthe following apparatus:. the ~b-ject, material to insulate t~eobject, a voltmeter, an ammeter,a clock, a thermometer, hook-upwires and a source of electricity.

7. Given an object made up of severaldifferent materials, determine anapproximate value for the heatcapacity of the object by esti-mating the masses of the differ-ent materials, looking up appro-ximate values for specific heatsof the materials, and performingthe appropriate calculations.

8. Given a control system based onthe thermal expansion of mater-ials (such as in the toaster),describe the sequence of eventsby which the thermal control mech-anism produces a desired result orprevents an undesirable one whenenergy is supplied to the device.

9. Given a process which involvesthe transformation of energy ampngseveral different forms and a listof energy forms, identify all formsof energy.which change during theprocess and state which are in-creasing and which are decreasingduring each stage of the process.

10. Given two of the following threequantities for an electric cir-

cuit, determine the third: volt-age, current, power.

11. Given two of the following threequ~ntitie8 for a circuit, deter-mine the third: time, power,energy.

12. An object is heated through arange in which the specific heatis constant. Given three of thefollowing four quantities, deter-mine the remaining quantity:heat, specific heat, mass, changein temperature.

13. An object is heated through arange in which the coefficientof thermal expansion is constant.Given three of the following fourquantities, determine the remain-ing quantity: change in length,original length, coefficient ofthermal expansion, change intemperature.

14. Given a bimetallic strip madeof known metals and a table ofcoefficients of thermal expan-sion, determine which way thestrip will curve when heated.

15. Given the appropriate formula,the dimensions and compositionof a bimetallic strip, the co-efficients of thermal expansionfor both metals, and the temp-erature change from the situ-

ation in which the strip wasstraight, calculate the ~ngleof curvature of the strip.

16. Given the appropriate formula,the dimensions and compositionof a bimetallic strip, the co-efficients of thermal expansionfor both metals, and the temp-erature change, calculate theamount of movement of one endof the str ip.

The toaster is a simple de-vice to operate: you plug it in,put in the bread, lower the mech-anism, and in a short time, np popsthe toast.

There are several interestingaspects to the toaster which mustbe studied if the principles of op-eration are to be understood. Anessential feature is that the toast-er produces heat by using electric-ity. This is an example of a gen-era1 process we see many times eve:cyday: energy changing frPflt one forrnto another. This process and thelaws of nature which govern ,itareof such great importance that weshall study them in some detail.

Before we discuss the process,the meaning of the word "energy"must be established. Energy is~ capacity to ~£ :.:~)!!~.Since wehave defined one scientific word,energy, in terms of another, work,we must be certai.n that we know themeaning of the wor d "work." If youpush a hand lawnmower across thelawn, you do work. If you raise abook from the floor to a table top,you do work. The amount of workdone by a force acting in the di-

rection of motion is equal to theforce multiplied by the distancemoved. With that in mind~ the de-finition should be more meaningful.A person (or an object) has energyif he (or it) has the capacity todo work. The best way to grasp themeaning of energy is to considerthe various forms in which it ap-

of energy results from the abilityof a raised object to do work. Ingeneral, an object in 8 higher pos-ition can do work in the process ofmoving to a lower position. Thistype of energy. associated with the

As the we;i.qhtf~llslt runemachinery which does ~ork.

potential !£ do work ~ ~ result 2!.the gravitational force, is called

Fig. 2. A compressed spring can moveobjects, thereby doing work.

Another common form of energyis the result of forces producedin stretching, compressing, bend-ing or twisting materials. Suchforces are called elastic forces.

~ potential !£ ~ ~ !!a result of elastic forces iscalled elastic potential energy.Consider this example of elasticenergy. When you lower the mech-anism which carries the bread intothe toaster, you compress a spring.Later, the elastic potential energyof the compressed spring does thework of "popping up" the toast.

If you have ever driven anail with a hammer, you have usedanother form of energy, called ki-netic energy. The work which canbe done !?1: .! moving objec~ .!.!! bein~brought !£ !!!!!!called kineticenergy.

("Kinetic" refers to motion.)

We distinguish between the two typesillustrated in Figure 3 by cal.lingthe first translational and the seq-ond rotation!l kinetic energy. Ifthe motion is described by referringto the turning about some axis, itis called rotational motion.

,Fig. 3A»The"hammer does work as itdrives the nail into thewood.tIg:-JB.-;

:'The 9rinding wheel does work;as the Wheel slows down, even;after the power is shut off.I.. , .

A form of energy which may notbe as familiar as the ones alreadymentioned is the energy associatedwith electricity. The energy asso-ciated ~ charge~ particles atrest or in motion is called electro-- -- --- ---- ----magnetic energy. In everyday life,this energy is most often used insystems which have charged particlesmoving through wires. This kind of

energy is often called simply ~-trical energy. Examples includethe energy required to operate thetoaster, electric motors, and elec-tric lights.

Fig. 4A.

Electricity runs the ~)tor,which does work.Fig. 4S.

.' ~di~:~'ves are capable of.doing work.

Charges at rest sometimes con-tain a form of electromagnetic en-ergy called electrostatic E.?t.~ntia~

enerjY. If you rub 8 balloon onyour hair on a dry day, the balloonacquires the ability to lift yourhair, or other small objects, andthus do work. Moving storm cloudsalso become charged and clearly de-velop the potential to deliver large

amounts of energy in the form oflightning bolts. The sudden lightand sound is caused by a huge el~c-tric current, and it is an exampleof electr:Lcal energy which resultsin work being done. But even be-fore the lightning strikes, thecloud has the capacity to deliverwork, and thus we say it has elec-trostatic potential energy.

Electromagnetic energy also ap-pears in the form of electromag-netic radiation. This includes--~,.,,,,,,---rad io and TV waves, light, ,X rays,and gamma rays (a gamma ray is e-lectromagnetic radiation producedby nuclear effects).

(,~J:~,

.Fig •...S.JThermal energy runs the steamengine.

A form of energy which keeps uswarm and does a variety of otherthings for us is called heat energyor thermal energy. ~.!! the ~-ergy ~h .!! trans.!~~ ~ ~

object ~ another be~ ~f .!temperature diff~~, Heat isusually involved in s',lell proc-esses as raising the temperatureof an object, melting and boiling.

As you read and turn thesepages, you are using a form ofenergy called chemical energy.Chemical energy is associatedwith all;£!.ocesses in which ~~ ~ rearranged to ~different substances (chemicalreactions), Examples of suchreactions include burning, theproduction of electrical energyin a battery, and the productionin a muscle of the energy neededto turn a crank.

The work done by the womancomes from the chemicalenergy in the food she .ate.

ergy to be used by man is nuclearenergy. The energy which comes

~ ~ co.re',£E. ~c leus, ~ !.h!~ .!! called ~~ ener~y..Among our energy resources, onlythe light and heat radiation re-ceived from the sun is greater thanthe presently known sources of nu-clear energy.

Fig. 7. Nuclear energy is changed to~hermal energy and the thermal .energy powers the submarine.

In summary, we identify the fol-lowing forms of energy:'

I. Mechanical energy(8) Gravitational potential

energy(b) Elastic potential energy(c) Kinetic energy (rotational

and translational)II. Electromagnetic energy

(a) Electrical energy(b) Electrostatic potential

ener,gy(c) Electromagnetic radiationHeat energyChemical energy

III.IV.

V.

It is possible to think ofmany different processes whichinvolve changes from one kindto another among the differenttypes of energy. For example,

when using nuclear ~nergy, heatis produced before the work is

l BATTERYCHARG I NG ••.••••

BATTERY

ELECTRIC HEATER

-~

Fig. 8. A few of the many differentenerqy transformations.

As the yo-yo unwinds, it dropslower, thus losing gravitationalpotential energy. But as it movesdown, it goes faster; therefore, thekinetic energy increases. Thus wehave an example of the change ofgravitational potential energy intotranslational and rotational kineticenergy. When the string is all un-wound, it starts rewinding; the yo-yoclimbs back up, transforming kineticenergy into gravitational potential

energy.You will find a clever example

of energy transformation in thepop-up mechanism on some toasters.When you push down the handle tolower the elevator mechanism, it

compresses a spring. When thetoast is done, the elevator is re-leased and the elastic potentialenergy is changed into other forms.Some goes into gravitational po-tential energy of the elevator andtoast. Some goes into translationalkinetic energy of the elevator andtoas t.

A difficulty appears when de-signing the elevator. If the springis made strong enough to lift theheaviest slices of bread, it willbe so strong it will throw thelightest slices into your cornflakes. When you examine the toast-er in the laboratory, you will seehow this problem is solved by caus-ing some of the elastic potentialenergy to go into rotational kinet-ic energy.

In almost all processes in-volving energy transformation, someheat is produced whether you wantit or not. In the two cases justdiscussed, the yo-yo and the toast-er elevator, the rubbing of one

surface on another produces heat en-ergy (but not much). As another ex-ample, an electric motor gets warmwhile running because of friction inthe bearings and because of resist-

Discuss the energy transforma-tions in the following devices orprocesses:

1) a flash light2) a wind-up clock3) a car moving at constant

speed4) a car accelerating5) a football thrown into the

Throughout the preceding dis-cussion of energy transformations,we have hinted at an idea: Energycannot be created or destroyed, al-though ~ form may be changed.This is a very fundamental law ofnature and is called the law of con-servation of energy.

In order to proceed with a mean-ingful discussion of the law, we muststate how to assign numbers to variousforms of energy. Descriptive termsare not sufficient; we need numbers.Although it is possible to do this forall the various forms of energy, we

will concentrate on the two formsof central importance to the toast-er: electrical energy and thermalenergy.

The amount of electrical en-ergy delivered to or by a circuitelement is determined by threethings: the current, the voltage,and the time.

Current is the rate at whichelectric charge flows through acircuit. The common unit for cur-rent is the ampere. The deviceused for measuring current iscalled an ammeter. (The name "am-meter" comes from "ampmeter," butfor some strange reason the "p" isleft out.)

*This treatment of electricity isvalid for all direct current cir-cuits and for many alternating cur-rent devices, including the toaster.

The voltage between two pointsin an electric circuit is equal tothe work done per unit charge as thecharge moves from the first point tothe second. Saying it another way,for simple circuit elements likeheating coils, a larger voltage a-cross the element causes a largercurrent to flow. The unit of volt-age is the volt; an instrument thatmeasures voltage is calLed a volt-meter.

The work that charges (elec-trons) do when they move throughthe wires of a toaster is to bumpinto atoms of the metal wire andcause them to vibrate. The energyof the vibrating atoms is the sameenergy we previously called heat en-ergy or thermal energy. If a cer-tain unit of charge produces 2 cal-ories of heat energy when it flowsthrough a resistor, and if 3 suchunits flow through the resistorevery second, then the heat energyproduced is 6 calories per second.(The calorie is a unit of heat. It

will be defined later).Since voltage is work per unit

charge and the current is rate offlow of charge (charge per unit time),the product of the two is work perunit time:

workcharge

chargetime

worktime

The rate of doing work (workper unit time) is ca Hed power.

In terms of the common symbols forthese quantities,

If the voltage is expressed involts and the current in amperes,then the power is in units calledwatts, one watt equals one volt-ampere. To give you some feelingfor the size of a watt, a personrunning up a flight of stairs usesabout 500 watts of power.

NOW IS THE TIME TO DO EXPERIMENTSland 2

Voltmeter

Connections

EXPERIMENT 1 - ELECTRICAL POWER -I~~ERSION HEATER

In this experiment you will meas-ure the electrical power delivered toan immersion heater and will comparethe measured value with the manufac-turer's rating for the device.

Since electric power is the pro-duct of current and voltage, it canbe determined quite easily throughuse of an ammeter and voltmeter. Tosimplify the wiring, a transfer boxis provided.

The immersion heater, voltmeter,

CAUTION: Be sure the transfer box isnot plugged in when you makeyour connections. Your in-structor will plug it in

AmmeterConnections

Place the heater in a cupof water before closingthe circuit; it will burn

Record the meter readings, thenunplug the heater. Compute the power.Does it agree with the rated powerstamped on the heater?

the toaster. Compare with the manu-facturer's rating.

Example 1. DE,terrninethe powerprovided hy 3 6 volt battery to a

P=VI= (6 vo 1t ) (2 amperes)= 12 (vo1t X ampere)= 12 watts.

* ,,< * "I( "1< ,,< 'Ok "1< "k '"k * * ,,< * * * *Example 2. A light bulb is

stamped "40 watts, 120 volts," Howmuch current will it draw when con-

Solution: In this case the power andvoltage are known and it is necessaryto solve for current.

P=IVPI= V

"" 40 \.Jat ts120 volt

40 (volt x ampere)120 volt

1= 3" ampere."1< ,'( * * * ,,< 'Ok .,'c "1< * -;( ,,< * "I( * -;< *In many cases we will be inter-ested not in the rate at which work

is being done, but the amount ofwork done during some time. Sincepower is the rate at which work isdone, just multiply by time to getthe work, or energy:

W = Pt

= VIt

If the power is in watts andthe time in seconds, then the workor energy is in watt-seconds. Thiscombination of units appears sooften we give it a name of its own;joule. That is, a joule is a watt-second. To give you a feeling forthe size of a joule, it is approx-imately the energy needed to lifta hamburger three feet.

Example 3. How much electri-cal energy is converted to heat andlight if a 100 watt light bulb isleft on for one hour?Solution:

W = Pt= (100 watt) (1 hour)- (100 watt) (3600 sec)= 360,000 joules

* * * * * * * * * * * * * * * * *Although the joule is the

unit of work and energy preferredby scientists, a more common unitwhen dealing with electricity isthe kilowatt-hour, abbreviated kWh.

It is the energy of a 1000 watt (onekilowatt) source run for a ti~e 'ofone hour. This is approximately theenergy needed to lift a car to thetop of the Empire State Building.The conversion between kilowatt hoursand joules is easily established:

1 kilowatt hr 1000 watt hr= 1000 watt (3600 see)= 3.6 x 106 watt-see= 3.6 x 106 joules

In circuit problems, it is con-venient to compute the energy directlyin units of kilowatt-hrs.

Example 4. How much energy isrequired to make a slice of toast?The toaster is rated at 1200 wattsand the toasting time is one minutExpress the answer in kilowatt-hrsSolution:

W = Pt= (1200 watts) (1 min)'" (1.2 kilowatts) (1/60 hr- 0.02 kilowatt-hr

* * * * * * * * * * * * * * * * *Example 5. If electricity co ts

2¢ per kilowatt-hr, for how manyhours will 50¢ run a 1000 watt spa eheater?Solution: At 2¢ per kilowatt-hr,will buy 25 kilowatt-hr. Knowingnumber of kilowatt-hr, we can solv

for the time:W • Ptt • W/p =

25 kw hr = 25 hrI kw* * * * * * * * * * * * * * * * *

Raising the temperature of anobject by rubbing it is a simpleexperiment which shows ,that workand heat are somehow related.

Fig. 13. ~ Rubpinq causes a temperature- 'rise.

Indeed it was just this type of ex-periment which led'to the identifi-cation of heat as a form of energy.Near the end of the eighteenth cen-tury Count Rumford noticed thatduring the drilling of cannon bar-rels, heat was produced for as longas the drilling continued. Laterexperiments proved that other formsof energy could be changed to heat,and vice versa. These observationsled to the statement of the basiclaw of conservation of energy.

However, long'before it was realizedthat heat is a form of energ~, sci-entists had studied the effects ofheat on such things as temperature,melting, and boiling. To explaintheir observations they assumed thata substance, which they called "ca-lorie," flowed from one object toanother during heating processes.Although we no longer believe thecaloric theory, a souvenir remainsin the name for a unit of thermalenergy, the calorie. A calorie isthe heat required to raise the tem-perature of one gram of water onecentigrade degree.

If heat is applied to a sampleof material, the temperature willrise. We find that the amount ofheat required is proportional to themass (m) of material and also pro-portional to the change in temperature(AT)*. That is,

Q • cmAT

where Q is the amount of heat and cis a constant for a given materialbut has different values for differ-ent materials. The constant c iscalled the specific heat. Note that

*The symbol A, which is the Greekletter delta, indicates the changein a quant ity.

The table below lists the experi-.mentally determined valuee o( spe-cific heat for several common sub-stances. (The values are the samein both the metric system of unitsand in the British system which willbe described shortly.)

from the definition of calorie,the specific heat of water is onecalorie per gram-centigrade degree.If the specific heat of a substanceis known, the amount of heat re-quired to increase the temperatureof a given mass of the material agiven amount can be determined.* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

BakeliteCopperGlass

LeadWater

0.2150.550.092

0.20

0.113

0.0301.00

Example 6. How much heat isrequired to raise the temperatureof 5 kilograms of iron six centi-grade degr.ees?Solution: Consulting the tableabove we find that the specificheat of iron is 0.113 cal/gm-Co.

Q ,.em T• (0.113 cal/gm CO (5000 gm)

(6 CO)

,..3.390 cal

mula Q = cmAT. m must be expressedin grams if you want Q to come outin calories. Some scientists pre-fer to express m in kilograms andthis will result in a value for Qexpressed in kilocalories. Thisunit for energy, the kilocalorie,is the same amount of convertibleenergy contained by food when adietician says the food containsone calorie. To say it another way,the "dietary calorie" is really a

kilocalorie.* * * * * * * * * * * * * * * * *

EXPERIMENT 3 - CONVERSION OF ELEC-TRICAL ENERGY TO THERMAL ENERGY

In this experiment you will de-termine the electrical energy pro-vided in heating a cup of water, andwill compare it with the increase inthermal energy.

The electric energy provided isequal to the product of the powerand the time. Therefore by addinga clock to the equipment used inExperiment I, you will be able todetermine the energy.

The increase in thermal energy,Q, is determined by the mass of water,m, the specific heat of water, c, andthe change in temperature, ~ T:

Q = mc.o T.

Plan your experiment. We sug-gest that you start with cold tapwater and heat it to about 80°C,inserting the heater nearly to thebottom of the cup. Stir gently butcontinuously. Before beginning,note which quantities must be meas-ured in order to calculate the elec-trical energy and the thermal energy.

After completing your measure-

ments, calculate the electrical en-ergy provided in joules and ehe in~.crease in thermal energy in calor~es.Compare the two by applying the ap-propriate conversion factor. Howwell do they agree? What factorscould cause the two values to differ?* * * * * * * * * * * * * * * * *

Another heat unit frequentlyused in English speaking countriesis the British thermal unit, ab-breviated B.t.u. A B.t.u. is theamount of heat required to raise thetemperature of one pound of waterone Fahrenheit degree.

Calories and B.t .U. IS are dif-ferent units for the same physicalquantity, energy. So they must berelated by a conversion factor. Andthey can both be related to the unitsfor energy introduced earlier, joulesand kilowatt-hrs. The conversionfactors for these energy units aregiven in the table at the top of thefollowing page.

one joule c 2.78 x 10-7 kwh

""0.239 cal..,9.48 x 10-4 B.t.u.

-6one calorie:;: 1.16 x 10 kwh

•..4.18 joule

= 3.97 x 10-3 B.t.u.

one kWh = 3.60 x 106 joule

= 8.60 x 105 cal..,3.41 x 103 B.t.u.

= 2.93 x 10-4 kwh

Example 7. How much energyis required to raise the temper-ature of 10 1b of copper from 70°to 250°F? Express the answer inB.t.u.'s, calories, joules,_ andkilowatt-hrs.Solution: We can apply the equa-tion

Q :;: cmAT.

Since the amQunt of material andthe temperatures are expressed inEnglish units, it will be conven-ient to do the calculation firstin B.t.u.'s. Consulting the spe-

tors in Table II to express the heatin other units.

Q ••• 166 B.t.u. (2i2 cal)4 .t.ll.

•.•4.18 x 10 cal

Q •• 166 B.Lu. (10~5 joule)5 •t .u.

• 1.75 x 10 joule

Q = 166 B.t.u. (2.93 x 10-4 kwh)-2 B.t.u.

• 4.86 x 10 kwh

Example 8a. How many caloriesof thermal energy are produced by a1200 watt toaster which stays on for

cific heat table we find the spe- one minute?cHic heat for copper. Solution: In Example 4 we calculated

(0.092 °Q •.. B.t.u./lb-F ) the energy for such a case:(10 lb) (1801<'0) W ..,Pt

"" 166 B.t.u. (1200 watt) (l min)Now we can use the conversion fac- =:: 0.02 kwh

Applying the conversion factor fromTable II

W r:: Q = 4 cal1.72 x 10* * * * * * * * * * * * * * * * *

Example 8b. How much watercan be heated from room temperature(200C) to the boiling point (lOOoe)by the heat referred to in example8a?

Solution:Q = cmATm • .JL

cAT 41.72 x 10 cal

•• (I cal/gmeO) (80eO) == 215 gm

This is approximately one cup ofwater.* * * * * * * * * * * * * * * * *

Example 9. An electric heateris imbedded in a 2 kilogram pieceof aluminum. The heater draws sixamperes at 120 volts. If the tem-perature of the aluminum is ini-tially 200e, what will it be at theend of five minutes? (Ignore anyheat losses to the surroundings.)Solution: From the information oncurrent, voltage and time, theamount ·of electrical energy can becalculated.

W •• VIt

== (120 vo'lt) (6 amp) (5 min)- 3600 ,,.,att-min== 216,000 joule

This energy appears as heat. Fordetermining the temperature change,.it is convenient to express thisenergy in calories.

1 calW == Q == 216,000 joule (4.18 joule)co 51,600 cal

Now we can use the equationQ == em AT.

Solving for ~ T.

AT •• Q/cm(51,600 cal)

== (0.215 cal/gmCO) (2000 gm)

== l20eoT = 200 + AT ••• l400efinal

Therefore the temperature at the endoof five minutes is 140 C.

* * * * * * * * * * * * * * * * *Another quantity often met in

dealing with heat problems is theheat capacity, K, for an object. Itis defined as the heat added to anobject divided by the change in tem-perature resulting. For example, if2000 cal.are required to change thetemperature of Some object by 10 Co,the heat capacity is 2000 cal divided

o 0by 10 e , or 200 cal/C. Note thatheat capacity is a characteristic ofan object whereas specific heat is acharacteristic of a material. Ifthe heat capacity of an object isknown, the heat required for a speci-fied temperature change is readily

Example 10. The heat capacityoof a pot of beans is 1500 ca~/C .

How much energy is required tooraise its temperature from 20 C to

900C?

Solution:Q •• K~T

•• (1500 caliCo) (70 Co)

•• 105,000 cal.

* * * * * * * * * * * * * * * * *For an object made up of sev-

eral materials. the heat capacitycan be calculated if the amount ofeach material and the specificheat for each material is known.

Suppose you have an object madeup of three materials, a,b,c,

cific heats ca' cb' ce' To producea temperature change AT in material'.a, the amount of heat required is

Q •• c mAT.a a a

Similar expressions apply for mater-ials band c. The total heat neededto raise the temperature of the en-tire object is

••cama.l::lT+ cbtnfT + ccmc.o.T

• (cama + cb~ + ccmc)ATThis same total heat can be expressed,in terms of K, the heat capacity:

Q =: K.bT.

Comparing the two expressions, wesee that the following must be true:

K ••cama + cb~ + ccmc·

This procedure can be used no matterhow many different materials are in-volved.* * * * * * * * * * * * * * * * *

In this experiment you willexperimentally determine the heatcapacity of the toaster and willcompare the result with a rough es-timate based on the mass and speci-

Recall the definition of heatcapacity; the heat capacity of anobject is the heat required to pro-duce some temperature change.

The amount of heat is equalto the electrical energy deliveredto the toaster. It can be deter-mined by measuring the power forthe toaster and the time duringwhich that power is applied. Sinceheat is customarily expressed incalories, it is appropriate to con~vert the energy in joules to energyin calories by applying the appro-priate conversion factor.

The change in temperature canbe determined by attaching a the~-mometer to the toaster. Howeverthere are some complications. Theheating occurs in'the heating ele-ments within the toaster, and ittakes some time for this heat tobe distributed so that the toasterwill have a uniform temperature.(In Experiment 3 you could keepthe water temperature uniform bystirring; unfortunately you cannotstir the toaster.) While you arewaiting for a uniform temperature,there will be considerable heatloss to the surroundings. This

effect can he reduced by placing aninsulating box over the toaste~, butthe losses are still appreciable •.Fortunately there is a way to approx-imate the effect of these losses andadjust your data accordingly.

Suppose that you plugged inthe toaster, left the power on fora minute or so. and then'removed theplug. You then record the temperatureas a function of time, taking readingsevery 30 seconds both while the poweris on and for 20-30 minutes after thepower is turned off. Don't stop untilthe temperature reaches the value ithad when the power was turned off. Ifyou plotted these data, the graphwould look like the solid line in thegraph below:

~"-i.': '" ""':,:,'>

,..-_ .•-~-.•;,._,, -,,IIIIII..

tton off

The temperature will rise onlyslightly during the short time that

the toaster is on because very lit-tle of the heat will have reachedthe location of the thermometer.If there were no losses, the tem-perature curve would follow thedotted line, approaching some finaltemperature as the heat gets dis-tributed throughout the toaster.The effect of the losses is to causethe temperature to follow the solidline. By noting the temperatureloss per unit time during the cool-ing part of the curve, you can ob-tain an approximate value for thetemperature loss during the risingportion of the curve. To do this,pick a time when the temperature ofyour toaster was just beginning tofall. Pick a later time at whichthe temperature had fallen to avalue equal to what it was when thepower was turned off. Divide thistemperature difference by the e-lapsed time in minutes. The num-ber you get is the average numberof degrees the temperature felleach minute over this temperaturerange. Multiply this number by thenumber of minutes the temperatureof the toaster was rising. Sincethe toaster presumably "lost" thismany degrees while it was heating,this number should be added to the

total observed increase to obtain theincrease we would have observed forthe same energy input if there had,been no heat losses to the surround-ings.

With the toaster unplugged andset for "light" toast, attach the ther-mometer to the end with the tape pro-vided, and lower the elevator. Care-fully place the insulating box overthe toaster, guiding the thermometerthrough the hole in the box. Wait afew minutes to be sure the temperatureis steady. Use the time to plan yourmeasurements and prepare your datasheet. You must record the current,voltage, and the time the toasterstays on after plugging it in. Tem-perature should be recorded every 30seconds during the early part of therun. Later. when the temperature ischanging more slowly, the measurementscan be less frequent.

Calculate the heat capacity ofthe toaster from the experiment data.

For a comparison with the ex-perimental value. a rough estimate ofthe specific heat can be calculatedfrom the mass and specific heat of thematerials in the toaster. To do thisit helps to have the toaster partlytaken apart. (Check with the instruc-tor before doing this.) This provides

you with three components whosecontribution to the heat capacitycan be computed separately; thesteel case, the "guts," and theend caps. The mass of each ofthese can be determined with abeam balance.

The contribution from thesteel case can be determined eas-ily by multiplying the mass bythe specific heat of steel (about

o0.1 cal/gm C ).The material in the end caps

is either bake lite or a similarmaterial. If you check tables ofspecific heat for such materials,you find that they all have a valueof about 0.5 cal/gm Co. Thus thecontribution from the end caps canbe estimated.

The contribution from the re-mainder of the toaster presents aproblem because there are many dif-ferent materials. However, if youcheck the specific heat for any ofthe materials which a.ppear in sig-nificant quantity, you find thatthey vary between 0.1 and 0.2cal/gm Co. Therefore if you use

oa value of 0.15 cal/gm C , your re-sult should be accurate to withinabout 25%.

From these three contributions

obtain your r'ough estimate of the heatcapacity and compare with the-value·determined from the heat and temp~r-ature measurement. Do they agree aswell as you might expect?* * * * * * * * * * * * * * * * *

Example 11. An object consistsof 2 kilograms of iron, 0.6 kilogramsof aluminum and 0.4 kilograms of ba-kelite. What is the heat capacity ofthe object?Solution:

K = (0.113 cal/gmCo) (2000 gm)+ (0.215 cal/gmCO) (600 gm)+ (0.5 cal/gmCO~ (400 gm)

= (226 + 129 + 200) calICo= 555 calICo

The preceding discussion hasprovided the basis for an understand-ing of the energy transformation (e-lectrical to thermal) which occursin the toaster. Another importantfeature of the toaster is the control'system, the mechanism for shuttingoff the current at the right time.Could this be a simple clock timer?No; it takes less time for the sec-ond batch than it does for the firstbecause the toaster is "pre-heated."The control system must somehow bebased on heat and temperature, not

time. To understand how this isaccomplished, it is necessary tobegin by studying a physical pro-perty called thermal expansion.

Have you ever noticed thatelectric power lines sag morE7 insummer than in winter? This oc-curs because the wires expand whenheated; this is called thermal ex-

A' ~,•• ,..J"......!I :

ILENGTH AT TEMPERATURE T. +' b. T

f . ,"

Fig. 16. tn this figure the amOunt ofthermal expansion is greatlyexaggerated.

Experiments show that the changein length; AL, is proportional tothe original length, L , and to theochange in temperature, AT:,

.AL = ol.L .o.T.o

The constant of proportionality, ~is called the coefficient of linearexpansion and its value depends onthe material. Table III gives theexperimentally determined values ofthis coefficient for several mater-

pansion. ials.* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

TABLE IIICoefficients of Linear Expansion

coeer poper

Aluminum 23 x 10.6 13 x 10.6

Brass 19 x 10-6 11 x 10-6

Glass (Pyrex) 3.2 x 10-6 18 x 10.6

Invar 0.8 x 10-6 0.4 x 10•.6Iron 12 x 10-6 6.6 x 10.6

Copper 17 x 10-6 9.2 x 10-6

Example 12. Determine thechange in length of a copper wire,originally 150 feet long, if the

otemperature is changed from 10 Foto 90 F.

Solution: From Table III, ot for-6 0copper is 9.2 x 10 IF.

..o.L=olLATo

= (9.2 x 10-6/Fo) (150 ft)(80P<»

• 0.110 ft • 1.3 in

This dependence of size ontemperature can be used in devicesthat measure temperature, and indevices that control temperature,such as the control mechanism ina toaster. Because the change inlength is very small, many of thesedevices use two different mater-ials in a clever w.aywhich has theeffect of magnifying the movement.The arrangement is called a bimetal-lic strip.

BRASS

'\t COOL

6i::. ;:t ;j#,,,,)'f~

WARM.~

\ Fig. 17. A bimetallic strip curveswhen heated.

Figure 17 shows such a strip. Thedevice consists of a thin st~ip ofiron attached to a thin strip ofbrass. If the temperature of thestrip is increased, both the ironand the brass will expand. However,the brass will expand about 1\ timesas'much as the iron because of itsgreater coefficient of expansion.How can the two have differentlengths and still remain fastenedtogether? The strip must curve, asshown in Figure 17.

Figure 18 shows an idealized"mode 1" of what rHlppenswhen a bi-metallic strip is heated. For ourn~del we are assuming that the stripcurves so that it is simply an arcof a circle whose radius is R. Theangle 0 is a convenient quantity to

Our task now is to predict 9 ; thatis, to find an expression for e interms of the original length, L0'the change in temperature,A T; thetwo coefficients of expansion, 0(, band tX. i' and the thickness of eachstrip, d.

First let us find 8 in termsof the length of the brass strip,Lb, and the length of the ironstrip, Li. Note that Li is a cer-tain fraction of the circumferenceof a circle; the fraction is 3foo.Therefore

Li = 3100 times circum-ference

= 3tocs 211'Rwhere

R is the average radius of the ironstrip. We can write down the cor-responding expression for the lengthof the brass strip, noting that theaverage radius for the brass stripis greater than that for the ironby an amount equal to the thickness,d;

Lb '"' 3goo 2 17' (R + d).

Subtracting,Lb - Li ..,'3':00 2 1f (R + d)

3foo 21TR

_ () 4Y- 3600 21/ d.

Solving for () ,

B= 3~~(\Li)

Now we can write expressionsfor the lengths of the two stripsin terms of their lengths when theywere straight (which were equal),their coefficients of thermal ex-pansion, and the temperature in-crease which caused the strips to

Lb • Lo + .bLb

= Lo +oLb LoAT.

Similarly,Li = Lo + OCi LoAT

Subtracting,L

b- L. = oI.

bL .aT - C(. L ~ T

1 0 1 0

= ( 0<.b - o(i) L0.6 T

Inserting this in the expressionfor (),

3600t7 = -2-

* * * * * * * * *

L ~To

Example 13. A bimetallic strip,made of iron and brass strips each0.01 inches thick, is straight andthree inches long at lOce. Deter-mine the amount of curving at BOoe,by specifying 8 .Solution:

3600 (19 x 10-6_ 12 x 10-~/Co (31n)(70B - - ...•...•o_._2 0.01in.

2dex> - ex.) .6 T

ti ~

2sit!

(0.:',- c<.)6Tp l

for cases where 8 is no 19rgerthan 30° which c:orre,:;ponds L:04S

will compare your experimental resultswith the relationship introduced in

L 2o «(>i. - i/..) A T

b ~

meanings:~S: distance traveled by free

end of stripL: length of strip

o

r:t •b" coefficient of linear ex-

pansion for brass

coefficient of linear ex-pansion for invar

With this apparatus you will beabl.e to vary the temperature of thewater. and measure the position of the

free end of the strip as a func-tion of temperature.Procedure:1. Measure the length of the strip.

from the scale to the pointwhere it enters the supportclamp.

2. Measure the thickness of thestrip at several points andobtain the average. (Note thatthis thickness is 2d.)

3. Fill the tray to within aboutone centimeter of the top withcold water.

4. Allow several minutes for thesystem to come to eqUilibrium.then record the temperatureand the position of the end ofthe strip.

5. Immerse the immersion heaterin the water and plug it infor about two minutes. Stirgently after removing the power.

6. Wait for about two minuteswhile stirring for the systemto come to equilibrium. thenrecord the temperature and theposition of the end of thestrip.

7. Repeat 5 and 6 until the tem-perature has reached approxi-

omately SO ,You now have data on position

versus temperature. Plot these dataon a sheet of graph paper. Do thepoints fall approximately on a st~aightline? Should they. according to equa-tion (l)?

From your graph. determine yourexperimental value for the change in

bSposition per unit temperature At.Using this value and equation 1. de-termine 0( b- cXi. How we 11 does thisagree with Table III? The agreementmay not be exact because the coeffi-cient for invar goes up considerablyfor small changes in its composition.* * * * * * * * * * * * * * * * *

Example 14. A bimetallic strip.made of iron and brass strips each0.01 inch thick. is straight and threeinches long at 100e. If one end isclamped in a fixed position. how muchwill the other end move if the tem-perature is increased to 80oe?

L 2o

.AS = 2d (r;J.. b- ext) AT

(3 in)2 (6.6 x 10-6/eo)(70eo)= (0.02 in)

Since the result is much lessthan Lo/4, it is not necessary to usethe more exact expression.* * * * * * * * * * * * * * * * *

quently used in electric circuitsto turn the current on and off asthe temperature changes. In thesimplest application its purposeis to keep the temperature constant,or static, hence the name thermo-stat.

The figure below illustrates

a simple thermostat circuit. The in-sulating material in the base 6f thethermostat cannot conduct a current.Therefore there will be a'current inthe heater only when the free end ofthe bimetallic strip touches the con-tact point at the right end. If itis touching, the heater will be on.

CONTACTPOINT

¥"POWER

SliPPLY

This causes the surroundings, in-cluding the bimetallic strip, toheat up. As the strip gets hotter,it curves away from the contactpoint, thus breaking the circuitand turning off the heater. As thetemperature goes down, the stripmoves back to the contact point andthe cycle repeats itself. A well-designed system of this type canhold the temperature variation toless than a degree.

In the above example the heat

source is an electric heater. In ahome furnace system, the circuit isused to start and stop the furnace.* * * * * * * * * * * * * * * * *

EXPERIMENT 6 - THE TOASTER CONTROLSYSTEM

In this experiment you will ex-amine the mechanism which "decides"when the toast is done and then shutsoff the power and pops up the toast.

Although the operation is not ter-ribly complicated, without someguidance it would probably takeyou a few hours to figure it out,largely because some of the im-portant parts aod important move-ments are difficult to see. Thesuggestions below are intendedto guide you through the oper-ation in a logical order.

CAUTION: Before beginningyour inspection of the system,be sure the toaster is un-

Lower the elevator and notethat this action closes the mainswitch on the toaster.

With the main switch closed,current can flow in the heatingelements, and in the control sys-

HEATINGELEMENTS

It is now clear that loweringthe elevator starts the cycle. Whatends it? When the elevator pops upthe main ~witch will open, endingthe cycle. Therefore you shouldseek the mechanism which releasesthe elevator so that the spring canpush it up. Note the solenoid inthe photograph.

A solenoid is an electromagnetwhich, when activated, pulls in aplunger. In the toaster, this action

releases the elevator. Demonstratethis by pushing down on the plungerwith your finger. The next obviousquestion is: what causes the sole-noid to be activated? If you ex-amine the circuit for the solenoid,you will find that the only thingpreventing a current in the sole-noid is the gap between the contactpoints indicated in the photograph.

The electrical hook-up for thesolenoid can be represented by theschematic diagram below.

STRIPHEATERCIRCUIT

What makes the contact pointsclose? At this point it is valu-able to see the control circuit inactual operation. In order to dothis without exposing you to dan-gerous temperatures or dangerousvoltages we have made modificationsin the toaster. These modificationsallow the control system to operatein its usual way, but the main heat-ing elements are by-passed, and thevoltage is reduced to a safe level.

First, be ~ that the powersupply is ~ plugged in. Your in-structor will plug it in after hehas checked your circuit.

Connect the toaster as indicatedin the photograph below, then ask the'instructor to check it.

Lower the elevator to start thecycle, and watch what happens. (Be-cause of the modifications, thetoaster will not get hot; otherwisethe events will be the same as in

normal operation.) In particularwatch the contact points which,when closed, activate the solenoid.

What causes the motion whichresults in the closing of the con-tacts? If you suspect a bimetal-lic strip, you are right. Whatheats the strip? The photo belowpoints out an insulating "stocking"which covers a small heating ele-ment wrapped around the bimetallicstrip. Although the stocking hidessome of the detail, you can see oneend of the heating element enteringthe stocking. The other end is

The electrical hook-up forthe strip heater can be repre-sented by the schematic diagramas shown in the right column.

think that this heater would be onall during the cycle, and simplycause the strip to curve until thesolenoid contacts are closed therebycompleting the cycle. However, theoperation is not that simple, as youwill soon discover. Try to deter-mine the circuit for the strip heater,with particular attention to the twopairs of contact points whose loca-tion is indicated by the photographbelow. (To aid in locating them, ared spot has been painted on top ofone pair and a green spot on top ofthe other.)

A, CONTACT POINTS FOR ACTIVATING SOLENOID.

B, CONTACT POINTS WHICH ARE OPENED TOBREAK THE STRIP HEATER CIRCUIT

C: CONTACT POINTS FOR BY- PASSING STRIP HEATER

until you hear a click, is straightdown from the top, as in the photo-graph belmy.a complete cycle. The best view

for the first part of the cycle,

Can you -figure out '("hatishappening? You will probably wantto watch through several cycles,since each cycle lasts for onlyabout a minute.

Perhaps you noticed that duringthe first part of the cycle, thestrip curves in such a directionthat the center

from the body of the toaster. ~fuenit clears the white block (pointedout in the next photo), "it movesup. This upward motion opens onepair of contacts, breaking the cir-cuit for the strip heater. Italso closes another pair, therebyby-passing the strip heater.

II ,.t

II 32

l~

With no current in the heater,the strip cools, and it begins tostraighten. The block preventsthe center from moving back in,therefore the free end moves 'out,eventually closing the solenoidcontacts and thereby completingthe cycle.

Why is the control system thiscomplicated? Why not simply havethe strip directly activate the so-lenoid, and omit the part of thecycle which causes the strip heaterto be by-passed? Hint: What wouldhappen if you tried to make a sec-ond batch of toast immediately after* * * * * * * * * * * * * * * * *

Example 15. In the systemshown below, should the materialin the top of the bimetallic stripbe the one with the higher or the

POWERSUPPLY

Answer: The material on top shouldhave the higher coefficient of ex-pansion. To decrease room tem-

the first?Here are some other questipns

you should consider:1. During the cycle the strip

clears the block and movesup. How does it get backunder the block?

2. How does the "Light-Dark"control function?

3. There are two adjustmentscrews near the left sideof the control system.What role do they play?

4. When the elevator pops 4P,a wheel spins. What pur-pose does this wheel serve?

* * * * * * * * * * * * * * * * *lower coefficient of thermal expan-sion? To lower the temperature inthe room should the adjustmentscrew be moved up or down?

AIRi CONDITIONER

perature the screw should be movedup.

The transformation of electri-cal energy to heat energy in thetoaster is an example of conserva-tion of energy; although the formof the energy is changed, the a-mount of energy is constant.

In an electric circuit, thepower is the product of the volt-age and the current. A unit forelectric power is the watt, whichis the same as a volt-ampere.

Power is the rate at whichwork is done, and the work doneby the charges in a curcuit isequal to the amount of energy de-livered. Thus the energy deliveredby an electric circuit is the powertimes the time, or the product ofthe voltage, the current, and thetime. If the power is given inwatts and the time in seconds,the energy is in units of joules.Another energy unit commonly usedin connection with electrical pro-blems is the kilowatt-hour, whichis simply 1000 watt-hours.

The two most common unitsfor thermal energy are the cal-orie and the B.t.u. (British Ther-mal Unit). A calorie is the heatrequired to raise the temperatureof one gram of water one centigrade

degree. A B.t.u. is the amount of·heat required to raise the tempe~-ature of one pound of water oneFahrenheit degree.

Different materials need dif-ferent amounts of heat to raisethe temperature of equal masses bythe same amount. This property isspecified by stating the specificheat: the specific heat of a mater-ial is equal to the heat added to asample of the material divided bythe product of the mass of the sam-ple and the change in temperature.

Heat capacity is a character-istic of an object, not a material.It is equal to the heat added tothe object divided by the change intemperature. Its value can be cal-culated from the masses of the ma-terials in the object and the spe-cific heats of the materials.

Most materials expand whenheated, but different materialsexpand different amounts for equalincreases in temperature. Becauseof this, a bimetallic strip willcurve when heated. This effect isutili~ed in control circuits, suchas that in the toaster, to open andclose electrical switches.

1. A flashlight is powered by twodry cells which provide threevolts. If the current is fiveamperes, what is the power rating,in watts, for the bulb?

2. A 300 watt heater is designed todraw 25 amperes. What is thedesign voltage'?

3. A certain car battery has thecapacity to provide 0.84 kilo-watt-hours of electrical energy.For how long can it run a 12volt motor which draws 300 am-peres?

4. An iron frying pan has a massof three kilograms. How muchenergy is needed to raise its

o 0temperature from 20 C to 220 C?Express your anSWer in calories,joules, kilowatt-hours, andB. t .u. •s.

5. For a particular thermos bot-tle 10,000 calories are re-quired to raise the temper-ature of the inside bottlefrom 20°C to loDe. What isthe heat capacity of the insidebottle?

6. A pound of water has an initialtemperature of 176°F. What isthe temperature of the waterafter losing 10,000 calories

of thermal energy to the air?7. A 200 watt i~nersion heater is

used to heat an insulated con-tainer of water. The amount ofwater is 400 grams. Assumingthat all the energy goes intoheating the water, determine therate at which the temperature

8. Determine the heat capacity ofthe following system: An elec-tric skillet consisting of 1.5kilograms of aluminum, 0.6 kilo-grams of glass, and 0.4 kilogramsof miscellaneous materials withan effective specific heat of 0.3.Inside the skillet is a stew con-sisting of 1.5 kilograms of waterand 2.5 kilograms of meat andvegetables having an effectivespecific heat of 0.8.

9. Determine the change in lengthof an aluminum wire originally200 feet long if its temperature. . 0 01S changed from 0 F to 100 F.

10. You have a strip of metal onemeter in length. It is knownto be either iron or invar. Youfind that when you change thetemperature by IOOoe the lengthchanges by an amount somewherebetween one-half and one-and-a-

RoomThermostat

SafetyRetet Stack

Control

---oi.i=='S'Q

NOTE: If the fuel ignites, the heat going up the stackcauses the stack control to close, shorting theheater in the safety-reset9ircuit. Otherwisethe safety-reset circuit will open and will beheld open by the latch until manually reset.

16. A container is divided intotwo parts by a verticle par-tition. A fixed temperaturedifference between the twoparts is to be maintained bymeans of a control systembased on bimetallic strips.In the diagrams below, the

shaded part of each bimetallicstrip is brass and the clearpart is invar. In each casethe strips make contact whenthey are at the same temper-ature. Determine which oneswill produce the desired re-sult.

I, f', IIII!rli

Iii

r- -J II,POWER rtr-

r'I .II

JII, I, II'

IpOWER~

I,.......-......._-__-----'.-1

!?Z{)P£'s san -/' 1'0'/' (~C.7;}nun{t;lj (~()lSt. I1Xlis, Missouri

Bill G. Aldridqe, PrDject Direct(KRalpll L. Ba.I:nett, ,Jr.I):)na1d R. M)\.\tCTY

Guy S. Walc1rHarlJ..•.~renc(' .J.. ~'hlfe)0hTJ. 'r. YcrlerArnold B. ALanf, (0. of Washington)StcV!::.m G. Sand~ni (Southern Illinois

UniVtc:Tsit_y at K'iwarc.rSville)

Carobr idiJ8 , Massachu •.setts

Nathaniel Frank, Principal InVf-.}stigatorF..n1est KleItIa, Pr.i ncipal Il1'vest.iqatorJohn W. McWane,Project DirectorRic.~a.rd LEwisllina Ibh:~rtslif.alcc)lm SmitllIbbc~rt'rin~{"=r

,T. David Ga'venda, Cha.irrranPl.-ofessor of Physics and Educat~ionUni '\1t;rsity o.f 'I'C'Y.i:lS

Austin, TexasKennetJ1 W. FordC11airroan, Departlrent~ of PhysicsUniversity of M3ssachusett-s, &x:;tonI3ost.on, f4issachUC:E·tt:s

Jam::~s L. Heins-elmanIh'ill of InstxucLionIDs Angeles Ci ty Colleq8Los Angeles, ('..ali forni a

:\lan HoldenF3<211 'I'elephr..:me Labs, fet.hedBox 46i~l Vern:Jn, New Jerr:>ey

:3rte(~i(xl .T~ra~in"irlf/ Dirv1:r;I()!?Oak l?iclge A;~;~oc~·taLedfJrrive:PDi ties

Oak. Ridge, Tennesseeh"1'h'rence K. Akers, Project DirectorJohn F. Yegge, Project Codi.D:;ctor.John ArrPndtbwdrd DicksonJerry fA.interHoner Wilkins

~Sl;(lte lJn'i''l)(:}''lD ~ity c f~Ne?L' YOi??c(1t 13i "!1 ~'-Ih<JJn -to r;~

Binghamton, Neil York

('..arl H. Stannard, Project Ccrlirector(SUNY at Binghamton)

Bruce B .M.'i.rsh, Project Codirector(SUNY at Albany)

Arnold Benton Ct!.m. Inst.. of Physics)Giovanni J:n{Jeduglia (Staten Is1 and

OJmmmity G.Jllege)Gdbriel KOu..SOurOll (QtEensooro C. C. )Jm'1 C!uderkirk (SUNY at_ Canton)Arnol.d [.;t..:ca.'-:;sennurg (5lJr'.1Y at Stony

Br00k and AAPT)L.P. Lange (Broorre Corrrrnmity College)Ml1colm Gc:Jldberg (y.Jes1:c'hester C.C.)

G~)rge H. KeslerD3p.-:lrtrrent M::lnaqer, :Mat.erials I.aboratoryi'l~D':lI1nell Aircraft CompanySt. I.ouis, t,tissouri

'.Iheod.o:t-e W. FoIl rteLlstructional DeVl~lor:m:.·mt. Specialistfr111as ClJunty eommmity C',ol1eqe DistrictDallas, 'rexa..s

Charles S. 5110UP, Jr.Director, Q'):q;orate IesearchCabot OJrpJrationBillerica, MassachusettsIDui.s v.brtrnanCoordinator ~ Electrorrechanical ProgramNew York City Commmity COllegeBrooklyn, New York

Address in<.JUiries to:

Phi.lip DiLavore, Project Ccx>rdinatorTedl. PhysicsIndiana State University'I'er:tB Haute, Indiana 47809