Electrical Equivalent of Heat

ELECTRICALENERGY

1987 PASCO scientific $5.00

ELECTRICALEQUIVALENT

OF HEAT

012-02833D5/94

HEAT

Instruction Manual andExperiment Guide forthe PASCO scientificModel TD-8552

IncludesTeacher's Notes

andTypical

Experiment Results

012-02833D Electrical Equivalent of Heat

i

Table of Contents

Section Page

Copyright and Warranty .................................................................................. ii

Equipment Return ............................................................................................ ii

Introduction ..................................................................................................... 1

Equipment ........................................................................................................ 1

Maintenace....................................................................................................... 2

Experiments:

Experiment 1: The Electrical Equivalent of Heat ...................................... 3

Experiment 2: Efficiency of an Incandescent Lamp ................................. 5

Teacher's Guide ............................................................................................... 7

Electrical Equivalent of Heat 012-02833D

ii

Please—Feel free to duplicate this manualsubject to the copyright restrictions below.

Copyright, Warranty and Equipment Return

Copyright Notice

The PASCO scientific Model TD-8552 ElectricalEquivalent of Heat manual is copyrighted and allrights reserved. However, permission is granted tonon-profit educational institutions for reproduction ofany part of this manual providing the reproductionsare used only for their laboratories and are not sold forprofit. Reproduction under any other circumstances,without the written consent of PASCO scientific, isprohibited.

Limited Warranty

PASCO scientific warrants this product to be freefrom defects in materials and workmanship for aperiod of one year from the date of shipment to thecustomer. PASCO will repair or replace, at its option,any part of the product which is deemed to be defec-tive in material or workmanship. This warranty doesnot cover damage to the product caused by abuse orimproper use. Determination of whether a productfailure is the result of a manufacturing defect orimproper use by the customer shall be made solely byPASCO scientific. Responsibility for the return ofequipment for warranty repair belongs to the cus-tomer. Equipment must be properly packed to preventdamage and shipped postage or freight prepaid.(Damage caused by improper packing of the equip-ment for return shipment will not be covered by thewarranty.) Shipping costs for returning the equipment,after repair, will be paid by PASCO scientific.

Equipment Return

Should the product have to be returned to PASCOscientific for any reason, notify PASCO scientific byletter, phone, or fax BEFORE returning the product.Upon notification, the return authorization andshipping instructions will be promptly issued.

When returning equipment for repair, the unitsmust be packed properly. Carriers will not acceptresponsibility for damage caused by improperpacking. To be certain the unit will not bedamaged in shipment, observe the following rules:

➀ The packing carton must be strong enough for theitem shipped.

➁ Make certain there are at least two inches ofpacking material between any point on theapparatus and the inside walls of the carton.

➂ Make certain that the packing material cannot shiftin the box or become compressed, allowing theinstrument come in contact with the packingcarton.

Address: PASCO scientific10101 Foothills Blvd.Roseville, CA 95747-7100

Phone: (916) 786-3800FAX: (916) 786-3292email: [email protected]: www.pasco.com

ä NOTE: NO EQUIPMENT WILL BEACCEPTED FOR RETURN WITHOUT ANAUTHORIZATION FROM PASCO.


1

Introduction

The PASCO Model TD-8552 Electrical Equivalent ofHeat Apparatus provides an experimental determina-tion of the quantitative relationship between electricalenergy and heat. Conversely, if the electrical equiva-lent of heat is accepted as a given, this apparatus canprovide a convincing demonstration of the conserva-tion of energy. With either approach, the experimentis easily extended to determine the energy efficiencyof an incandescent lamp.

Instructions for two experiments, along with studentworksheets, are on pages 3-6. In Experiment 1, the Electri-cal Equivalent of Heat is experimentally determined. Anincandescent lamp is immersed in a known quantity of waterand a few drops of India ink are added to the water so it isopaque to visible light. The temperature of the water ismeasured. The lamp is then illuminated with a fixed current

and voltage for a measured time interval, so the electricalenergy into the lamp can be calculated. By monitoring thetemperature of the water, the heat produced by the lamp canalso be calculated. The ratio between the electrical energythat flows into the lamp and the heat produced by the lampdetermines the electrical equivalent of heat.

In Experiment 2, the efficiency of the incandescent lamp ismeasured. The details are similar to Experiment 1, but noindia ink is added to the water. Without the ink, the thermalenergy and infrared radiation from the lamp are absorbedinto the water, but the visible light escapes. To determinethe amount of energy that was released as light, the heattransferred into the water is subtracted from the totalelectrical energy that flowed into the lamp . The ratiobetween the light energy and the electrical energy gives theefficiency of the bulb.

Equipment

Your Model 8552 Electrical Equivalent of Heatapparatus includes the items shown in Figure 1: atransparent Electrical Equivalent of Heat Jar (EEH Jar)with a built-in 35 Watt incandescent lamp, twostyrofoam Calorimeters, and a bottle of India ink.

➁ A digital Volt-Ammeter (a separate voltmeter andammeter are best) for measuring the power input tothe lamp. (Such as PASCO Model SE-9589.)

➂ A clock or stopwatch to determine the electrical en-ergy that flows into the lamp (energy = power xtime).

➃ A thermometer, or PASCO's TD-8559 ThermistorProbe.*

➄ A balance for accurately determining the mass ofthe water heated by the bulb.

(* A digital ohmmeter (SE-9589) is recom-mended for use with the Thermistor Probe.)

➤ IMPORTANT: When using the ElectricalEquivalent of Heat Apparatus, always observethe following precautions:

➀ Do not fill the water beyond the line indicatedon the EEH Jar. Filling beyond this level cansignificantly reduce the life of the lamp.

➁ Illuminate the lamp only when it is immersedin water.

➂ Never power the incandescent lamp at avoltage in excess of 13 V.

Additional Equipment Needed:

In addition to the equipment included with yourElectrical Equivalent of Heat apparatus, you will needthe following items to perform the experiments in thismanual:

➀ A regulated power supply capable of delivering upto 3 A at 12 V. (Such as PASCO Model SF-9584.)

Figure 1 Equipment


2

Maintenance

Replacing the Incandescent Lamp

A. The Easy Way

Order the Lamp Assembly directly from PASCOscientific (Part Number 003-02956). Remove the oldassembly as shown below and replace it with thePASCO replacement.

Lamp Assembly

Bottom of Lid Top of Lid

Screw (6-32X3/8 P.H.) 610-014Black Connector 517-010Red Connector 517-009

Lamp Assembly Components:Bulb 526-019Bulb Holder 648-02954Standoff 648-02955

Calorimeter 740-02975India Ink 725-003

EEH:Jar 650-026Lamp Assembly only 003-02956Top Assembly 003-03124(includes Modified Lidand Lamp Assembly)

Modified Lid Components:Modified Lid Cover 648-02953Lid Plate 648-02952Label 646-02834

Part PASCO Number Part PASCO Number

1. Remove the lid ofthe EEH Jar

2. Unsolder and disconnectwires from banana plugterminals.

3. Unscrew Lamp Assemblyfrom lid of EEH Jar.

4. Reverse the procedure toreplace the entire LampAssembly (PASCO PartNumber 003-02956)

Figure 2 Replacing the Lamp

B. The Hard WayThe incandescent lamp is a common one that can bepurchased at most auto parts stores (Bulb 1157). Followthe procedure shown below, then, WEARINGGLOVES TO PROTECT YOUR HANDS, pull thelamp out of the plastic tube. You will have to solderwires to the replacement lamp. When you install thenew lamp, seal it in position with RTV Silicone Rubber.Be sure the seal is water tight. Replace the lampassembly and resolder the wires to the banana plugterminals.

Replacement Parts

The following replacement parts can be ordered fromPASCO scientific. Call for prices (Toll-free 1-800-772-8700).


3

Experiment 1: The Electrical Equivalent of Heat

Figure 1.1 Electrical Connections

+ –+–

+–

Power SupplyVoltmeter

Ammeter

13 V Max!

➀ Measure and record the room temperature (Tr).

➁ Weigh the EEH Jar (with the lid on), and record its mass (Mj).

➂ Remove the lid of the EEH Jar and fill the jar to the indicated water line with cold wa-ter. DO NOT OVERFILL. The water should be approxmately 10°C below room tem-perature, but the exact temperature is not critical.

➃ Add about 10 drops of India ink to the water; enough so the lamp filament is justbarely visible when the lamp is illuminated.

➄ Using leads with banana plug connectors, attach your power supply to the terminals ofthe EEH Jar. Connect a voltmeter and ammeter as shown in Figure 1.1 so you can mea-sure both the current (I) and voltage (V) going into the lamp. NOTE: For best results,connect the voltmeter leads directly to the binding posts of the jar.

➅ Turn on the power supply and quickly adjust the power supply voltage to about 11.5volts, then shut the power off. DO NOT LET THE VOLTAGE EXCEED 13VOLTS.

➆ Insert the EEH Jar into one of the styrofoam Calorimeters.

➇ Insert your thermometer or thermistor probe through the hole in the top of the EEH Jar.Stir the water gently with the thermometer or probe while observing the temperature.When the temperature warms to about 6 or 8 degrees below room temperature, turn thepower supply on.

➤ NOTE: You may want to turn the lamp on to help the cold water reach thisstarting temperature. If you do, be sure that you turn the lamp off for several minutesbefore you begin your measurements, so you are sure the water temperature is eventhroughout the jar. Record the starting time (t

i) and the temperature (T

i).

➈ Record the current, I, and voltage, V. Keep an eye on the ammeter and voltmeterthroughout the experiment to be sure these values do not shift significantly. If they doshift, use an average value for V and I in your calculations.

➉ When the temperature is as far above room temperature as it was below room tempera-ture (T

r - T

i = Temperature - T

r), shut off the power and record the time (t

f). Continue

stirring the water gently. Watch the thermometer or probe until the temperature peaksand starts to drop. Record this peak temperature (T

f).

Weigh the EEH Jar with the water, and record the value (Mjw

).


4

Data

Tr = _________________________________________

Mj = _________________________________________

Mjw

= ________________________________________

V = _________________________________________

I = _________________________________________

ti = _________________________________________

tf = _________________________________________

Ti = _________________________________________

Tf = _________________________________________

Calculations

In order to determine the electrical equivalent of heat (Je), it is necessary to determine both

the total electrical energy that flowed into the lamp (E) and the total heat absorbed by thewater (H).

E, the electrical energy delivered to the lamp:

E = Electrical Energy into the Lamp = V . I . t = __________________________

t = tf - t

i = the time during which power was applied to the lamp = ________

H, the heat transferred to the water (and the EEH Jar):

H = (Mw +M

e)(1 cal/gm C)(T

f-T

i) = __________________________________

Mw = M

jw - M

j = Mass of water heated = ____________________________

Me = 23 grams. Some of the heat produced by the lamp is absorbed by the EEH Jar. For

accurate results, therefore, the heat capacity of the jar must be taken into acount (The heatcapacity of the EEH Jar is equivalent to that of approximately 23 grams of water.)

Je, the Electrical Equivalent of Heat:

Je = E/H = _______________________________________________________

Questions

➀ What effect are the following factors likely to have on the accuracy of your determinationof J

e, the Electrical Equivalent of Heat? Can you estimate the magnitude of the effects?

a. The inked water is not completely opaque to visible light.

b. There is some transfer of thermal energy between the EEH Jar and the room atmosphere.(What is the advantage of beginning the experiment below room temperature and endingit an equal amount above room temperature?)

➁ How does Je compare with J, the mechanical equivalent of heat. Why?


5

Experiment 2: Efficiency of an Incandescent Lamp

Repeat Experiment 1, except do not use the India ink (step 4) or the styrofoam Calorimeter(step 7). Record the same data as in Experiment 1, and use the same calculations to deter-mine E and H. (Convert H to Joules by multiplying by J

e from the first lab.)

In performing the experiment with clear water and no Calorimeter, energy in the form ofvisible light is allowed to escape the system. However, water is a good absorber of infraredradiation, so most of the energy that is not emitted as visible light will contribute to H, thethermal energy absorbed by the water.

The efficiency of the lamp is defined as the energy converted to visible light divided by thetotal electrical energy that goes into the lamp. By making the assumption that all the energythat doesn't contribute to H is released as visible light, the equation for the efficiency of thelamp becomes:

Efficiency = (E - Hj)/E.

Data

Tr = ________________________________________

Mj = ________________________________________

Mjw

= ________________________________________

V = ________________________________________

I = ________________________________________

ti = ________________________________________

tf = ________________________________________

Ti = ________________________________________

Tf = ________________________________________


6

Calculations

In order to determine the efficiency of the lamp, it is necessary to determine both the totalelectrical energy that flowed into the lamp (E) and the total heat absorbed by the water (H).

E, the electrical energy delivered to the lamp:

E = Electrical Energy into the Lamp = V . I . t = __________________________t = t

f - t

i = the time during which power was applied to the lamp = ________

H, the heat transferred to the water (and calorimeter):

H = (Mw +M

e)(1 cal/gm C)(T

f-T

i) = __________________________________

Mw = M

jw - M

j = Mass of water heated = ____________________________

Hj = H J

e = ____________________________________________________

Me = 23 grams. Some of the heat produced by the lamp is absorbed by the EEH Jar. Foraccurate results, therefore, the heat capacity of the jar must be taken into acount (The heatcapacity of the EEH Jar is equivalent to that of approximately 23 grams of water.)

Efficiency:

E-Hj = _________________________________________________________

E

Questions

➀ What effect are the following factors likely to have on the accuracy of your determination ofthe efficiency of the lamp? Can you estimate the magnitude of the effects?

a. Water is not completely transparent to visible light.

b. Not all the infrared radiation is absorbed by the water.

c. The styrofoam Calorimeter was not used, so there is some transfer of thermal energybetween the EEH Jar and the room atmosphere.

➁ Is an incandescent lamp more efficient as a light bulb or as a heater?


7

Teacher’s Guide

Experiment 1: The Electrical Equivalent of Heat

Notes on Procedure

➀ This measurement is not critical.

➇ It is important that the water temperature is uniformwhen you begin. If you use the bulb to bring thewater temperature up to its starting temperature, letthe system rest for a few minutes, then start.

Notes on Calculations

Je = 4.184

This is also the conversion between Joules andcalories: 1cal = 4.184J.

The result obtained experimentally should bewithin 5% of this value.

Experiment 2: Efficiency of an Incandescent Lamp

Notes on Calculations

It is critical that you change your value of H fromcalories to Joules for the efficiency calculations. Ifthe students have gotten good results for J

e in the

first experiments (within 5% of 4.184) have themuse that value for the conversion. Otherwise, or ifthey haven’t done experiment 1, useJ

e = 4.184.

Notes on Efficiency

The efficiency will vary depending on the voltageand the bulb. Generally-accepted values for theefficienty of incandescent lighting are on the orderof 10-15%. With our test bulb at 11.6V, the effi-ciency was measured as being 13%.

Notes on Questions

➀ a. Leakage of visible light will have negligible ef-fect, since most of the output of the bulb is notvisible. In addition, much of the visible light thatescapes is reflected back into the water by thewhite inside walls of the calorimeter cup.

b. This is the most significant source of error. Be-ginning and ending equal distances above andbelow room temperature will tend to create self-cancelling errors.

➁ Je is the same as J, since mechanical and electrical

energy are equivalent.

Questions

➀ a. Absorbtion of visible light will decrease themeasured efficiency.

b. Transmission of infrared will increase the mea-sured efficiency.

c. Conductive and Convective heat losses will in-crease the measured efficiency.

➁ The bulb is much more efficient as a heater than asa light source.


8

Notes


9

Technical Support

Contacting Technical Support

Before you call the PASCO Technical Support staff itwould be helpful to prepare the following information:

• If your problem is with the PASCO apparatus, note:

Title and Model number (usually listed on the label).

Approximate age of apparatus.

A detailed description of the problem/sequence ofevents. (In case you can't call PASCO right away,you won't lose valuable data.)

If possible, have the apparatus within reach whencalling. This makes descriptions of individual partsmuch easier.

• If your problem relates to the instruction manual,note:

Part number and Revision (listed by month and yearon the front cover).

Have the manual at hand to discuss your questions.

Feed-Back

If you have any comments about this product or thismanual please let us know. If you have any sugges-tions on alternate experiments or find a problem in themanual please tell us. PASCO appreciates any cus-tomer feed-back. Your input helps us evaluate andimprove our product.

To Reach PASCO

For Technical Support call us at 1-800-772-8700 (toll-free within the U.S.) or (916) 786-3800.

Documents

Electrical Equivalent of Heat