physics73.1 laboratory manual

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PHYSICS 73.!IABORATORYMAI\TI.]AL

by'

Nathaniel P. Hermosa IIMaricor N. SorianoJohannes AbatelMichelle F. BailonNelson CarcyEric GalaponGiovanni TzpangAlexander Mendenilla

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Fist Edition, Jurre 2000Second Edition, June 2001Edited by:Michelle BailonNathaniel HermosaPaul Eric Parafial


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Policies and guidelines i

EXPERIMENTS1. linear expansion 1

2, newton's law of cooling 93. specific heat capacity of some metals 25

4. heat of fusion of ice 3l5.photoelectric effect 456. calibration of the spectrometer 55

7. spectrum of hydrogen and other elementalvapors 658, visual absorption spectroscopy 79


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r. GRADING SYSTEMSrudents will be graded as follows:l-aboratory ReportsFormal Reports @,xpts 3,7)Data Sheets (Expts 1.,2,4,5,6,8)Recitation, Quizzes, etcRelativity/Modern Physics Otal ReportingDemonstration Experiments\\'ritten Exam

GRADE EQUIVALENT

600h20%40%10%1.0%5%15%Total 700oh

-+-+-)-+-+B. REQUIREMENTS

Students are required to submit at least two (2) FORMAL REPORTS and six (6)r\IFORMAL REPORTS. Reports will consist and will be graded as follows:

92.S x < 10088


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. Formal reports are to be submitted one week after the experiment has been pedormed whileinformal reports are to be done during laboratory hours and therefore must be submitted after class.r Reports submitted late will have deducion of 2Ao/o per day late.r Formal reports will be done in pairs while informal reports are done individudly.. The oral reporting shall be done by group.. Quizzes are at the discretion of the laboratory instructors'r { make-up experiment shall be given to those students who missed experiments but have a validexcuse.M-ake-up expedments must be done within the week scheduled for the expedment. If notpossible, a common Make-up day will be arranged.. Students can only make-up ior ONE experiment. The thirty items, one and a half-hour written final examination will be given in multiple choice.. A student who fails to submit at least five (5) experiments before &opping may be given a grade of5.0 if the student does not DROP the course.' A student who misses the FINAL examination may be given a gtade of INC, if he has attained agade of 45o/o andabove, otherwise the sdudent will be given a grade of 5.0.

SOME SOURCES OF DEMONSTRATION EXPERIMENTSA. JOURNAIS1. The Physics Teacher2. The AmericanJournal of PhYsics3. Levinstein, H. "The Physics of Toys", Physics Teacher 20,358(1982)B' ?:?tfl"rs, H.F., Physics Demonsffation Experiments, 1970 (fteiger, Melboume, FL 19xx)Z. Sutton, R.M., Demonstration Experiments in Physics, (IVIcGraw-Hill, New York, 1938)3. Caqpenter, D. RaeJr and Minnix, Ri.trra 8., The Dick and Rae Physics Demo Notebook, (Dick

and Rae,Irxington, VA 1993)SOME SOURCES OF ARTICLES FOR ORAL REPORTING1. Discover2. Physics Today3. Nature4. New Scientist5. Popular Science6. Science7. Scientific American

National Institute of Physics


7/94

INTRODUCTIONThe change in length per unit length perdegree rise in temperature is called thecoefficient of linear expansion. In equation form,it is given by

(1.1)L"ATvhere cr is the coefficient of linear expansion,Lo and Lr are the initial and final lengths,respectively, and AT is the change intemPerature.

OBJECTIVETo determine the coefficient of expansion of various metals using the micrometer screw type of linear

The value of o for solids or liquids doesnot vary much with pressure, but it may varysignificantly with temperature. However, theaccuracy obtained by using an average value of oover a wide temperature range is sufficient formost Pu{Poses.

METHODOLOGYA- MATERIALS

You will need the following items for this experiment.r .inss Expansion Apparatuso Copper or Aluminum Rodso power Supplyo Connecting Ifires (w/ Alligator Clip$. Rags

Ask assistance from your instructor.

Table 1.1 Coefficient of Linear

Iiri:o:I Institute of Physics, UP Dilimao

o Stove


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1. linear expansionPhysics 73. I

dTrrEter

Figute 1.1 Linear Expansion Apparatus: The Micrometet Screw Type.

2.

The appanrus shovm above is designed formeasuring increases in the length of a metal rodby means of a micrometer screw. The screw Arests firrnly against one end of the rod inside themetal iacket. Once adiusted and a teading istaken of the position of the micrometer screw BB. PROCEDUREt. Measure the length of the metal rod using a

meterstick.fnsert the metal rod in the iacket throughthe end corks and place the iacket in theframe.Tighten the top scre\I/s iust enough to holdthe jacket in place with one opening at thebottom. Lead this tubing into a closedbeaker below the aPParatus.Adjust and fix screw A and check themicrometet screw B. Turn B until contact isestablished and the ammeter deflects.Place the digital thermometer in the topcork and twist it down with the cork in theopening until the temPerature probe is closeto the rod but not touching it.Record the initial readings of themicrometer screw Go, might need toreview on how to read the Micrometer) and

3.

at the other end of the rod, screw A must notbe moved because it is the datum fot theincrease in length. An electric circuit is used toindicate the instant that the tip of screw Bmakes contact with the end of the rod bydeflection of an ammeter.

the thermometer. Then turn back screw Bto about trvo fi.rll turns so that expansion isnot hampered.7. Fill the steam generator two-thirds full ofv/ater and place it above the electric stove'

8. Connect the tube from the steam generatorto the uPPer oPening'9. Switch on the stove and allow the water toboil. lBE CAREFUL NOT TO SCALDYOUR HANDS!10. Take the micrometer screw reading everyfifteen-(15s) seconds until a constant

maximum teading is obtained. Rememberto turn back sctew B two full turns afterevery reading so as to hampet the rod'sexpansion, If the steam is passed thtoughto long, the framework expands and themaximum increase' of the rod is notmeasured.

4.

5.

6.

National Institute of Physics, UP Diliman


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Phpics 73.1 [. linear expansionName: Date Performed:

Date Submitted:

Section:

Partners:

Instructor:

DATA SUMMARYRod # 1:

Iength:

time (min.)

C-oefficient of Linear Expansion (Ave.):% Error :\aioad Institute of Physics, UP Diliman


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Physics 73.1 1. linear expansionRod # 2:

Length: lenph:Time(rrtin)

temp. ('C) temp. fC) length (*r".)

Coefficient of Linear Expansion (Ave.):o/oErtor:

Natiooal Institute of Physics, UP Dilimen


11/94

Ptysics 73.1 1. linear expansion

EXERCISES1. Plot AL/L" vs. AT. Use the daa in your table to plot a curve in the gridlines ptovided below.Rod 1

LL/Lo

Rod 2

AL/L,

AT (c)

riii1-':f-i--i-f jriJ'', i 1-l'j iill .1,r-i. i.iji-ir-t-i -i -i-i i l.l- r+-!-j-it-i.-l i--!-i- I, -f- l..i tiii .i l- i i--j, t r:-lr:l_j_l_ l^r-*,:.i_r ii_ii.i-j. i,i r:r i''i' ji ijti-ili-1"t: -!+-r-jitiiiIi i,t.i--i-1"i .ii'-j-i--_L-i _ fi+i 'fi,l-j-J"i-.{.-

i-l'i-iril i;i1- .ili:-it:, ri-i -l -!- r ijii-i l-ij t-i i_ iiiiiii ijji-i.r-l--ii !, ,-L i.l i.j', i.i'' 1; iT i-r-l llli! l'-r'ii-'f-i-l ri# Ii--f L.ii'+i--i iirii-l tr--f -t--1-- +"t-i l- r--!r.-r t l':$1t iti i-l-j t-t,-i. i l--i l_r , _i-1-i-i 1"i-t-l r-i -1 i:l;i I -1--t- i:1t: 'f -,- Li i-j:-1--i--,-,i--ii ii ii -i I r-i--l'r i-r'+-i:[]: t- f-i iill-:il-riil +i itr_ --_l i-l r Ir .i i-i

-i-.i1--l-T.-i-t

t t-t:- lrlj ti i;ii-l lr: i- .t ii-1- .i;.r:',i,i :i:i i: i"j.i..i-r ji i +l 1.1-,: .: ir,i ii-iilI i 1-r il; i r-i-, i-' !i ih ii rir i j- t li-f,iiji'lt i, 'iilr,'1-l- iliir_i i; j.r,-i,, t, ;"i'i; :l tir+ i i'i j, i, ii :i:ij.+ | |il-r.i-,,: il -i-.i-i.l-r- i. i.1- "i -i-.r- ll; i':li l-t.i-i"+ -+

-!-i-f-j'i I i1't-i+,i

-l -l-.- | ".j "-i"i-r-j--r l-i !-r-r- i -i- j'it -fi-i'i"j-.r- ,-. l'l-i r'1 : 1,'it j,,r,, tiijil i-i- i ",, ,t- r-'i'ii-ii; -' i' ',a-i i .l--'!li- i.ii;j ii1!l-i l:i.ti

l'1-f l-,i_1.

,- iiiI ji -i'i:1 -.l !-! i-i-r j--l .'r :i- iit'jlI; f-l 7t :i.j.l.ii+ r-ii f-i- r lilrli',! -1--r.!-:ii t-i-i-t-1 i-i il-li:ij iil 1,, i;i:'lj i ', i-i'-fi_Iit,'ii-1-t- j "1...1-tii:1, 1- li-f-j' iii ii.i- lii -f i--i-i-1"-l- -i-1 f+i--+---ir;if 1r-i it-l' , i'liil il ii i1ilij.ti-++-l iJ:i",i.j- ii.iij'1" !i riti :ir:r.-i i-l-i i i.:' rr -i i- +i |:; 'ii,it', -i I- i'l'iil iii -f ii:li,ti1 irri, t:i il'iili. iii1 ii., .ii i1 r ii-i-n-;-i i'' i;ifi-r, 'r-i.: i,:ijjj -i + f-i1 i-: :-irlj. iif_i ",.,.+ -j-"'r-1 r .i--r-i- i-i t\r| ', I'r -i ir :i;ilr-ii ririil I i. il iiri -t- a- i-i-,1:i'i

-l--i j::: ii;:i i-i-i'l'ifij: i il: -1i',ti.' iji i l:i i-iLil.:i 1:i1 'ir-i-!!lil i.+ii;-i ,lii t:liit..i i-i'i tli jl:+iliiii 1r l; i;iji-i_'-1_-i-j-i l-1-i ii i-.1 1,,I1lAT cc)

.',.i.i+li i-i I-j.-i,-i.i. ir I-t. j-i;if.i..i 1r l-r-- li i-r--f-llrli"iiij .j-i.ij -j .L-.;--i-ti-r_r' iiiti),,1 i-i'-l-'r;. '!-1, 'j- ;i-i i;.r ir-l.l I',i l; lli.i I fl

:i1 i1r..l _

ii 1 +-ir.i j_f' :ili;

I I r-ll i, ii ;ii,l iifi--f-r i ", i- t'i +i- -:-i .l-j.i.i.j--i.1.;.i 1j.j',-i i r: _i_r i' i l+,1:i-ri :ij-i: i lf -i- :i j ii i.. .li.ililtarif l il . i i_i:i!i i- r-, -ijirri i il .-lj..i. .r.-i-r.:.1 i-1+ ii| t irii i.."_ --a ..t- '1"I -i ',ii: :,1;il'1 i-:i:1 i I i"i:i..i.j. + il.j-alii..t ia |ii..i.j.i,1i::1i1 ii..iiltil :r-i i i.i: l-,r-i-i;1iii1i-iI + f jjii i.l1a t ii { tt. -t ti-l"jll'-i' r,i.r_-i. ,)liL .1- iii i.'i.;'i ;.1 r':-i-il..i.j i I ti i,.

.jti"i-i 1 i-ji-i ;fl lr j_ii"ii-'f f1i r'i'rtt_ i:tii i1i-.i"i.-i iij , t jr ,1i i:.iii ilii i.,i -i--ia:: i-i. i -i l., ''i ' 1..1;lri" ii'--:- ;r-tl ttii L:+.j -i'-i.l' lt iiij ir l tlitji..r,.j. t;. ,ti-j i ii 1-

r-li--i -li-t _9

11 :i.r'lri 1l ii -, 'j 1)"i-i 1i :ij-_r 1 'il..::i\ i_-::.,i.. j. -i {" ;,t_

i-' -i i-r ,i T' t. -;)t t, ,.i,t i ij.iii 'i i.,. ^;.i. i,; 1 .,., 1, i':;-1.-i j.i.-i-l-.i-j--''i';' I-i_1'_i'.'i-i l'iirt::, 1 i i-:li-i-j -l t:i

Enl Irutitute of Physics, UP Dilimaa


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2. Compute for the coefficient of linear expansion of each rod using the different regions seen inthe earlier graph as well as the whole graPh.

3. Compare the values obained in (2) with the theoretical value. What is the Toerror for each rod?

QUESTIONS1. Explain the result of the LL/L"vs. AT plot. \[hy are there different regions?

Explain the results obtained in Exetcise 2.theoretical value? Why?

In which part of th. grPh is the o nearest to the2.

Nationd Iostitute of Physics, UP Diliman


13/94

tt6ks 73.1 L linear expansion3. How will the value of c be affected if it was measured in a different temperature range (..g. ,much higher or much lower temperarure range)?

In this experiment we used the length of the rod at room temperature (as opposed to its lengthat OoC) as our initial temperature. Did this inuoduce significant errors in the computed valuesof the coefficient of linear expansion for each rod?

ilb kstinrte of Physics, UP Diliman


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5. Cite the possible sources of error in the experiment. What improvements must beto minimize the errors in the experiment?

SAMPLE CALCUI-ATIONS



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INTRODUCTIONThermodynamics relates energy transfersbetween a system and its uurroundings tochanges in the state of the system. There aretwo types of energy transfers, heat and work.An energy transfer occurdng by virtue of atemperature difference between the system andits surroundings is called heat. If the energytransfer is not connected with temperaturedifference, it is called work. Since heat transfer,Q, and work, $7, can proceed on either of twodirsstisn5, into or out of the system, a signconvention is adopted.Q is positive for heat taken in\U7 is positive for work done by the systemUsing the sign convention, the principle ofconservation of energy as it applies todrermodynamics is given by

dQ =du +dw Q.1)dU is the change in intemal energy of thesystem between two equilibrium states which isdU = CdT (2.2)

where C is the heat capacity of the systemaoid dT is the change in temperature.dW , on the other hand, is the work done indre system.Assuming that the work done in the systemis negligible compared to the intemal energyaod to the net heat, the energy equationbecomes

dQ=dU =CdTThis can also be written in

excess temperature a(t) asdQ= Cda(t)where a(t) =T(I)-TA andembient temperature.

dQ,rhe net heat input, can also be expressed asdQ=dQ,*-dQ,in terms of the input heat, dQ,* , and the heatwhich leaked out from the system, dQ..dQ,* is given by

dQn't = Pdt Q.6)where P, is the net power and d/, is theamount of time used to heat the system.It is also known that the heat leakage currentdQr l dt is proportional to the temperaturedifference a, and the proportionality constant,ft, is the effective heat ffansfer coefficient.Thus we have,

dQ, = ha(t)dt Q.7)Combining equations Q.4), Q.6) and (2.7), wehave

Pdt - hadt = Cda (2.8)The solution to this differential equation isgiven byd(t) = Ib-exp(- ?)]*oo'*p(- +) e.s)where x =+ and ao -f -To. Thederivationhis left as a problem.When P = 0, or during the cooling process,

d,(t)=oo"*P(- fl ?This is a solution to the NewtontsCooling equation,_da _adtr

Q.s)

Q.3)terms of the

Q.4)TA is the

Q.1(Law

Q.

Nrtional Institute of Physics, UP Diliman


16/94

OBJECTI\rESTo veri$, Newton's Law of Cooling.To gain knowledge on the heat leakage in a calorimeter.To obtain the heat capacity of the heater, stirrer and the probe.

METHODOLOGYA. MATERIALS

You need the following items for this experiment.Calorimeter Set-upPower SupplyAlligator Clips

REMINDERSo Do not turn on the heater if it is not fully

immersed in water.o The stirrer should be turned on during theexercise i.e., before the T, and until the lasttemperature reading.o The water-jacketed enclosure is meant tomake the ambient temperature of thecopper cup and its contents substantiallyconstant during the exercise. Make sure the

Ask assistance from your instructor.o Digital Thermometero Watet

jacket is almost filled with water. The covetshould be in place throughout theexperiment

Figue 2.1 The Calorimeter Set-up fot the Measurement of the Heatl*alcage Current.Nationd Institute of Physics, UP Diliman


17/94

flqssb 73.1 2. newton's law olcooling

B. PROCEDUREIn the set-up shown in figorc 2.1., thefollowing quantities are either given or readilymeasured.r\ = mass of water, 80 gC.u = heat capacity ofcopper cup !R = resistance of heaterTA - ambient temperature or temperatureof the enclosureConsider as a system the copper cup and itsontents. The system is in an initial state atEslperature T, near the ambient temperature,T{. Electrical energy is then added to the

s_Tstem at a constant rate for 600 seconds, whichcluses the temperatute of the system to rise to$ome temperature Tr, corresponding to \rhatre shall consider a final stage.1. Assemble the calorimeter as shown inFig.2.1.2. Take the ambient temperature.3. Now consider as the system the coppercup (inner calorimeter) and all itscontents. The copper cup and all itscontent are assumed to be in thermal

equilibrium with each other.4. Record the temperature inside thecopper cup. This is the inirialtemperature T,.5. Turn the heater on for 10 minutes.Take the temperarure, T(t), of thesystem every 30 seconds during the timeinterval the heater is turned on and untilthe maximum tempefature, T-"* isreached.6. Upon reaching T-"*, take thetemperature readings at 3O-secondintervals for tuzenty minutes.

!"icrrul Institute of Physics, UP Diliman


18/94

2. newton's law of

National Iostitute of Physics


19/94

Physics 73.1 2. newtont law of coolingName: Date Performed:

Date Submitted:

Section:

Partners:

Instructor:

DATA SUMMARYMass of Copper CupResistance of the Fleater Used:Ambient Temperature, Tr;

Mass of Water:Voltage Supplied to Ffeater:Initial Temperature, Tr:

HEATING

0 36030 390

60 42090 450L20 480150 510180 5402t0 570240 500 TH:270 630300 660330 690

!&irrllnstitute of Physics, UP Diliman


20/94

2. newtoa's hw of

COOLING

f,mar t*+630t.a'*30 t--+660t."r*60 t*+690t-o*90 1*+720t-o* 120 t*+750r*+ 150 t*+780r*+ 180 r*+810t*+210 t-*+840t^o*240 t*+870t*+270 t-o*900t*+300 h*+930t."** 330 t*+960t-o*360 r*+990t*+390 t-o+ 1020t*+420 r*+ 1050t*+450 t-*+ 1080t*+480 t*+ 1110tu*+510 t*+ 1140t.o+ 540 t*+ 1170r*+570 t*+ 1200t-"**600

Nationd Institute of Physics, UP Diliman


21/94

Ptrysics 73.1 2, newton's law of coolhgEIGRCISES1. Plot the temperature vs. time curve for heating and cooling.

Uo(u

(crro&oH

Eul Institute of Physics, UP Diliman


22/94

Physics 73.1 2 newton's law of cooling

2. Make a graphical representation of the cooling databy plotting Ln crvs t. Should the resultingSaph be linear? Use the formula for Newton's Law of Cooling to Prove this.

time (seconds)

3. Determine the numerical value of the constants o. and t.

t6 National Institute of Physics, UP Diliman


23/94

Physics 73.1 2. newton's law of cooling4. Plot the heat leakage current as a function of the excess temperature

Excess Tempetaturecr cc)

Compute for the heat tranqfer coefficient.

P?oItrilt\dE

Natinal Institute of Physics, UP Diliman


24/94

Phvsics 73.1 2 newton's law o[cooling6. tWhat is the combined heat capacity of the heater, probe and stirrer? Show complete solution.

Nationa.l Institute of Physics, UP Diliman


25/94

Plrynics73.1 , , . , . -2,newton'slavofcoolingQTIESTIONS1. Get the net heat leak, Q1 fot heating and cooling, separately. You can either use equarion (2.8) orQ.e).

Institute of Physics, UP Dilirnan


26/94

Phvsics 73.1 2 newton's law of coolingJ2. Provided that no phase changes occur, why should the amount of hea't leakage during heating be

less than that during cooling?

What is the dominant heat transfer mechanism responsible for the measured heat leakagecrureflt? Explain.

Why is it desirable to have the water a few degrees above thetemperature is taken? when the initial

Natiorul Institute of Physics, UP Diliman


27/94

Nl/" O tr61 t{ec es

Edlnstitute of Physics, UP Diliman


28/94

Physics 73.1 =1!!'rto!!,]aw illgoling.6. Show that as t approaches infinity, the heat leakage cuffent approaches the input power, P.What does this i-ply?



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Physics 73.1 2. newton's law of cooling7. Show that equation Q9) is a solution to Newton's Law of Cooling Equation.

8. Give appiications of Newton's Law of Cooling.

[5n] Institute of Physics, UP Diliman


30/94

Physics 73.1 2, newton's law of

National Institute of Physics, UP Diiiman


31/94

INTRODUCTION

This experiment follows from therheoretical background presented in the 2"dexpedment. After knowinq the specific heatcapacity of parts of the calorimeter and thus,

OBJECTIVESTo obtain and compare specific heat capacities of metals.

Caiorimeter Set-upPower SupplyAlligaot ClipsDigital'Ihetmometer

calibrating it, we are nov/ ready to use thecalodmeter to determine specific heats of somemetals.

To apply knowledge gained from heat leakage cuffent from the previous experiment.}fETHODOLOGYA. MATERIALS

You need the following items for this experiment. Ask assistance from your instructot.o lVatero Aluminum Cylinderso Lead pelletso Iron

REMINDERSo Observe precaution of the resistor,water-jacketed container, and stirret asin the previous experiment. In addition,make sure that the stirrer does nottouch any of the solid objects around it.

o The aluminum cylinders should be fullyimmersed in water, but use the leastamouflt of water as possible

liroonal Insdtute of Physics, UP Dilirnan 25


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Physics 73.1 3. specific heat capacities

stYrofoam aluminumcylindersFigute 3.1. Set-up fot Measutement of the Specific Heat Capacity.

PROCEDURE1. Assemble the calorimeter as shown inFig. 3.1. The only diffetence betweenthis set-up and that in the formerexperiment is that you will addingmetals into your copper cup..2. Take the ambient temperature. Makesure that the initial temperature, \,should be equal to or a few degreesabove the ambient temperature, T,.3. Turn the heater on for five (5) minutes.Take the temperature, T, of the systemevery thirty (30) seconils during the time

interval that the heatet is tumed on untilthe maxirnum temPefature, T*, isreached.Upon reaching T-o, take theter,nperature reading agir at thirty (30)second intervals for ten (10) minutes.Repeat steps 1 to 4 for the succeedingmetals given to you by your instructors.

26 National Institute of Physics, UP Dilirnan


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Physics 73.1 3. specific heat capacities

Name:

lnstructor:

DATA SUMMARYMass of Aluminum CylindersMass of Copper CupResistance of the Fleater Used:lmbient Temperature, Ta:

HEATING

HEATER OFF

Date Performed:Date Submitted:

Section:

Mass of 'W'ater:Voltage Supplied to Fleater:Initial Temperature, Tr:

Partners:

0305090120150180210240270300330360390

}uciooal Institute of Physics, UP Diliman


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Specific Heat CapacitiesCOOLING

t-o*330

Temperature Profile

Uo{,k+J(lkruaE!(uH



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M,qs of Lead pellets:}[-.s of Copper Cup:Bc


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il:1li:i:iii:l1,ffiffitm t-o+330

t-o*30 t*+360t*+60 t-*+390t-of 90 t^*+420r--+ 120 t*+450t-o+ 150 t-o*480t*+ 180 t*+ 510t*+210 r*+ 540t*+240 t*+ 570t*+270 t*+600t*+300 t*+630

Temperature Profile

Uoruk(!ikq)aEruF{

time (minutes)Naiiond Institute of Physics, UP Dilimall


37/94

Phvsics 73.1 1 qnpeifie haat ro.o"iti""

Mass of IronMass of Copper CupResistance of the Heater Used:Ambient Temperature, Te:

HEATING

HEATER OFF

Mass of 'lUfater:Voltage Supplied to Fleater:Initial Temperature, Tr:

0306090t201501802t0240270300330360390

Nrbnal Institute of Physics, UP Diliman 31


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COOLING

Temperature Profile

Uotulic!tiq)a(l)F{

r*+210

time (minutes)National lnstitute of Physics, UP Diliman


39/94

EXERCISES1. Compute t for the different metals.

2. Compute the heat transfer coefficient for the different metals.

Dhixral Institute of Physics, UP Dilirnan


40/94

3. Determine the specific heat capacities of the metals. Also, calculate the molar heat capacities.

4. Compute the 7o eror.

'National Institute of Physics, UP Diliman


41/94

hfics 73.1 3. specific heat capacitiesQUESTIONSl. Cite possible sources of error in the experiment.

Compate your obtained value of molar specific heat capacities with other substances. Explainyour observations.

Institr:te of Physics, UP Diliman


42/94

SAMPLE CALCULATIONS

National Institute of Physics, UP DiEman


43/94

AU = L8 = mL, * -{:r., (4.1)OBJECTIYE

To measure the heat of fusion of ice.

![ETHODOLOGY.L EQUIPMENTYou need the following items for this experiment. Ask assisrance from your instructor.

L\TTRODUCTIONFor every crystalline substance at a given

f,ressure there exists a definite tempefaturecalled melting point) at which the substance;hanges from sold to liquid when a definitei:rrount of energy per unit mass (cailed heat of::sion) is taken in.Consider as system rr\ grams of ice at its

=elting point. If heat, Q, is taken in until all the:ce has changed to water (at melting point Tx)xrd subsequendy raised to a temperature Tr, the:hange in internal eflergy of the system is

where L is the heat of fusion of ice. We haveassumed that the work done by the system isapproximately equal to zero.For the system pertaining to the givenproblem, the icefwater, which is within thesystem, absorbs heat mainly from the heater. Itschange in internal energy is given by equation(4.1). The energy balance equation for thissystem is obtained by applying the First Law ofThermodynamics and noting that the internalenergy change of the icefwater system, thestudent should work out the dstail5.

Digital ThetmometerCrushed Ice

removing melted ice at the beginning of theexercise.. Keep the cover in place during d,atagathering part of exercise.

Calorimeter Set-upPower SupplyAlligator Clips

REMINDERSr Observe precautions in setting up theheater, stirrer and the water-iacketedenclosure as in previous exercises.r Use a syringe with a piece of plastic tubingattached to it as a suction pump forx;iirosflal Institute of Physics, UP Dilirnan


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Physics 73.1 4. heat of firirn

StyrofoamFigure 4.1. Set-up for Measurement of the Heat of Fusion of Ice.

B. PROCEDURE1. Set-up the calorimeter as shown above.The stirret, thermometer probe, andheater must be completely immetsed in

ice.2. Monitor the tempetature until it reachesa constant temperature (monitoring timeis approximately 1 minute).3. Pump out the melted ice. Add more iceif the heatet has ,k."dy beenuncoveted. Make sure that thete isminimal water in the cup before tumingon the heater.4. If step 2 md 3 are properly performed,tum the heater ON and take the

temperature reading every thirty (30)seconds setting the time as equal to zerowhen the heatet is tumed on.5. Tum the heater off when it temperatureis already a five degtees above ambient6. Continue monitoring the temperatureuntil the maximum temperature isreached.7. Upon reachingT*, take thetempemture teading again at thirty (30)second intervals for ten (10) minutesNOTE: MAKE SURE TI{AT THESTIRRER IS ON THROUGHT THEDURATION OF THE EXPERIMENT.

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Physics 73.1 4. heat of fusion

Name:

DATA SUMMARYMass of Copper Cup:Mass of r$(/ater'!flithdrawn:Resistance of the Fleater Used:Ambient Temperature, Ta:

Date Performed:Date Submimed:

Section:

Mass of Ice:Mass of \7ater Left:Voltage Supplied to Fleater:Initial Temperature, Tr:

Partners:

Instructor:

Maximum Temperature, Tmax:HEATING

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Physics 73.1 4. heat of firionCOOLING

tri* t*+330t*+30 t-**360t**60 t-,*+390t-o*90 t*+420t-** 120 t-o+450t*+ 150 r*+480t..*+ 180 t*+ 510t*+210 t*+540t*+240 t*+570t*+270 t-o*600t*+300

E)(ERCISES1. Compute heat leakage using Newton's Law of Cooling.

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'1dhr',f k -]fu haidr.rn p'ir^tYYu" "^f"? tl'il ho I


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QUESTION1. Make a temperature profile of the system. (Iempetature versus time for heating and cooling)

time (minutes)2. Can you get an estimate of the heat of fusion of ice from the plot of temperature vs. time?

Uo(u

dtiru&oF

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SAMPLE CALCULATTONS

l{56mal ihstiture.'ciFPtryiti*;,t-tf-rOinmaii 43


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INTRODUCTION

By the late 1800s many physicists thought*rey had explained all the main principles of the:niverse and discovered all the natural laws. But:.s scientists continued working, inconsistencies--hat couldn't easily be explained began showing.rp in some areas of study.In 1901, Planck published his law of:adiation. In it he stated that an oscillator, orany similar physical system, has a discrete set of:ossible energy values or levels; energiesbetween these values never occuf.Planck went on to state that the emission:.nd absoqption of radiation is associated with

=ansitions or jumps between two energy levels.The energy losr or gained by the oscillator isemitted or absorbed as a quantum of radiantenergy, the magnitude of which is exptessed by:tre equation :E =hu (s.1)where E equals to the radiant energy, V is-:he frequency of radiation, and b is arundamental constant of nature. The constant hbecame known as Planck's constant.Planck's constant v/as found to havesignificance beyond relating the frequency andenergy of light, and became a cornerstone of thequantum mechanical view of the subatomicq-orld. In 1918, Planck was awarded a NobelPrize for introducing the quanrum theory of

-ight.In photoelectric emission, Iight strikes araterial, causing electrons to be emitted. Theclassical wave model predicted that as thentensity incident light was increased, theirnplitude and thus the energy of the waveq'ould increase. This would then cause moreenergetic photoelectrons to be emitted. The:lev/ quantum model, however, predicted that

higher frequency light would produce higherenergy electrons, independent of intensity, whileincreased intensity would only increase thenumber of electrons emitted (or photoelecuiccurrent). In the early 1900s several investigatorsfound the kinetic energy of the photoelectronswas dependent on the wavelength or frequency,and independent of intensity, while themagnitude of the photoelectric current, ornumber of electrons was dependent on theintensity as predicted by the quantum model.Einstein applied Planck's theory and explainedthe photoelectric effect in terms of the quantummodel using his famous equation for which hereceived the Nobel Pize in 7921.:

E = hu = KE^u* +Wo (5.2)where KE* is the maximum kinetic energyof the emitted photoelectrons, and IV, is theenergy needed to remove them from the surfaceof the material (the work function). E is theenergy supplied by the quantum of light known

as photon.A light photon with energy iv is incidentupon an electron in the cathode of a vacuumtube . The electron uses a minimum IY" of itsenergy to escape the cathode leaving with amaximum energy of KE,*in the form of kineticenergy. Normally the emitted electrons reachthe anode of the tube, and can be measured asphotoelectric current. However, by applying areverse potential V bettyeen the anode and thecathode, the photoelectric current can bestopped. KE,"*can be determined by minimumfevefse potential needed to stop thephotoelectrons and reduce the photoelectriccuffent to zeto. Relating kinetic energy tostopping potential gives the equhtion:

(s.3)

\:rional Insurure of Physics, UP Diliman

KE^* =I/s45


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5. ohotoelectric eftttDL.,^:^- 7? 1 _Therefore using Einstein's equation,hu =Vb+Wo . . (5,4) , \.Jd'tr

rlJIAooOroUa

When solved for V, the equation becomes:"tl

v =(L\,-f%) (s s)\e) \e )If we plot V vs. V for differeot ftequenciesof light, we will get a graph similar to Figure 1'-wThe ZintercePt is equal to :e- and the slope. h r. : .---r r^-^*' 'is 1. Coupling our expedmental detetminatione-of the ,^io L with the accepted value of 1'602ex 10-" coulombs, we can determine Planck'sconstant, ,.

METHODOLOG\A. MATERIALS

You need the following items for thisexperiment. Ask assistance from yourinstructor.o Photoelectric set-upo Green and Yellow Filterso Variable Transmission Gtating

Figure 5.1. Plot of the Stopping Potential vs'

Digitd Multi-meterAlligator CliPs

oo

oBJECTTVETo obsewe the particle ProPerty of light'To determine the work function of a matenzlTo detetmine Planck's constant.



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Physics 73.1 5. photoelectric effect

PROCEDUREPart A1. Adjust the h/e apparatus so that only

one of the spectral colors falls upon the 1.opening of the'mask of the photodiode.For the green and yellow spectral lines,place the coresponding colored fi"lterover the white reflective mask on theh/e apparatus.Place the variable transmission filter infront of the white reflective mask (andover the colored filter if one is used) sothat the light passes through the sectionmarked "1.00oh" and reaches thephotodiode. Record the DVM voltagereading in the data table in part A. Pressthe instrument discharge button, releaseit, and observe approximately howmuch time is required to recharge theinstrument to the maximum voltage.Move the vadable transmission filter sothat the next section is directly in frontof the incoming light. Record the newDVM reading, and approximate time torecharge after the discharge button hasbeen pressed and released.Repeat step 3 until you have tested allfive sections of the filter.Repeat the procedure using the secondcolor of the spectrum.

Part B

You can easily see five colors in the mercurylight spectrum. Adjust the h/e apparatus sothat only one of the yellow colored bandsfalls upon the opening of the mask of thephotodiode. Place the yellow colored filterover the white reflective mask on the h/eaPPafatus.Record the DVM voltage reading (stoppingpotential) in the data table of part B.Repeat the process for each color of thespectrum. Be sure to use the green filterwhen measuring the green spectrum.Move to the second order and repeat thePfocess.

2.2.

3.

4.

3.

4.

5.

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Physics 23.1 5. photoelearic effectName: Date Performed:

Date Submitted:

Section:

Partners:

Instructor:

DATA SUMMARYPART A

Col0r.#*..','.1...,.%fram i : #$ffi#i..trifii!iii; {}:il100

80

40

60

20

q100

80

40

50

20



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Physics 73.1 5. photoelectric effectPART BFirst Order Color ;ffl$rffi.,ffii@fi =,l1i!:sffiYellow

Green

Blue

VioletUltraviolet

+.ffift159,Wfl!$Hs *s#$13,tr#ffi ;,rwtr.u.ttll \-rr(lcr \/utur.#.$di$lffi;,:.1.. 1: 1 lr..::1! l:,t ./r--:;,'Iti=:i:.;lftft1$:1i:i:7-,-i:.:flE: :/=1,..'.,i::,i.l= T -';rl.'1, :,..1 ;l+i=l:t:i$;l;1.1;:i;:;-.r,., ..it=;::.,]:11::11'r,"r"::..r:i".1-;-.f i'r:';. l1 .:t.Green

Blue

VioletLJltraviolet

EXERCISES1. Determine the frequency of each spectral line.

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2. Plot a graph of the stopping potential vs. frequency.stoppingpotential(V)

frequency(1/s)

Determine the slope and the y-intercept of the above graph. Inteqpret the results in terms of theL ,^ro.e

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QUESTION1. Describe the effect that passing different amounts of colored light through the variabletransmission filter has on the stopping potential and thus the maximum eflergy of thephotoelectrons, as well as the charging time after pressing the discharge button.

Describe the effect that the different colored light had on the stopping potential and thus themaximum energy of the photoelectrons.



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3. Explain why there is a slight &op in the measured potential as the light intensity is &creased.

Defend whether this experiment supports a wave or quanrum model of light based on your labresulrc.

APPENDIXTable 1. The wavelengths of the Mercury Spectra

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INTRODUCTIONThe spectrometer is a device used toproduce and quanti4/ spectra. As depicted infigure 6.1, the spectrometer has three criticalparts: (1) a collimator; Q) a platform with eithera gating or prism holder; and (3) a telescope.The grating is placed ofl top of the platform andis secured when the spectrometer is calibrated.In using these devices, the angtiarmeasurement forms a critical part of theprocedute itself. Though personal biasesdominate angle readings, it is important to know

how these readings are made. The circular mainscale on the spectrometer platform is graduatedfrom 0 to 360o rvherein each division is equal to1/z degree. Adjacent is a vernier scale that has 30divisions. \Mhen the zero of either the vernierscales match with a division with a division onthe main scale, the 30'h division on that verniercoincides with another main scale. There are 20divisions between the 0 and the 30s division invernier scale indicating that each divisioncorresponds to Q9 /30) of a main scale division.The angular reading can therefore be made to aprecision of one minute.

Light from a light source enters thespectrometer through a narrow entfance slit. In

can be varied in order to change the amount oflight that enters the spectrometer. This beamthen passes through the collimator, whichproduces parallel beam of iight rays. These lightrays pass through the grating commonlydescribed in terms of the grating constant.Light coming ftom the grating is viewed withthe telescope either along the line of thecollimator or at some angle. If the apertures areparallel to the slit, diffracted lines may beviewed on either side of the normal image. Thespectra lying nearest the direct image on eitherside are called the first (1st) order while thosesuccessively more distant ^re called secondorder, third order, and so on.

Calibration of the spectrometer involves notonly the calibration of the spectrometer itself,but also the determination of the diffractiongrating constant D.

The diffraction grating is a simple but usefultool introduced by J. Fraunhoffer (1787-1828)which is commonly utilized to study thestfl.rcture and intensiry of spectral lines andmeasure the wavelengths of these lines. Atypical grating consists of a grid of fine parallellines with uniform spacing on a polishedmost spectrometer models, the width of this slit reflecting or transmitting surface.

A. Actual set-up B. Top view

,i+(JCLE

.IE.ESCFE

Fig. 6.1 Schematic diagram of a spectrometet.National Institute of Physics, UP Diliman 55


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physic 73.1 0. .aiuo,io" "r *" tp""tt

Fig. 6.2. The ttansmission gtating with incident light a and b and an adiacent gtating distance of d.Glass plates are commonly used for diffractiongratings while gratings ruled on metals are calledreflection gratings because the interferenceeffects are viewed in reflected rather than intransmitted light [1].

These grating lines, usually numberingbetween 60 to 600 lines per millimeter, are ruledwith a fine diamond point. The unruled portionof the surface, either by reflection ortransmission, set up the diffraction andinterference effects that form the spectrum oflight from a source. Figure 6.2 shows a crosssection of a common type of grating ruled onglass.

Now, consider a set of parallel rays from amonochromatic light source arriving at the slitsat right angles, as shown in frg. 6.2. The raysleaving the slits are diffracted. These diffractedrays interfere with one another until th.yproduce a fnal pattern.

The difftacted ray makes an angle 0 fromthe incident ray. Between any two diffractedrays, the interference is constructive (amaximum, observed as a bright line) whenevertheir path difference is a multiple of zwavelength. Since the path traveled by eachdiffracted ray is equal beyond the segment OP,the path difference would only be due to thedistance from the slit to the segment dP alongeach ray. For example, the path differencebetween a' and b', zs shown in figure 6.3, isgiven by

path difference = d sin9 , (6.1)where d is the distance between the slits.

For constructive interference, we havedsin0 'mL, (6.2)

where rn is an integer (0, t1 , t2, ...), andis known as the order of the maximum. Form = 0, 0 = 0 , hence the maximum is locatedsuaight across the screen. This is known as theprincipal maximum. There ate still several brightlines located on each side of the principal

Figute 6.3. Enlatgement of a potion infig.6.2maximum. Adjacent to the principal maximumis the first order naxinam (m=+1), followed bythe second order maximum (m =fl), and so on(see figure 6.4).If the light source is not monochromatic,several sets of color bands will be observed.Each set of color bands is known as thespectrum of the light source. Figute 6.5 shows a



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Physic 73.1 6. caLibration of t}te spectrometer

veryfaintred yellow brightdoublet greenfaintblue-green

brightblue-vioilet fa in tviolet

690.54 579.06671.64 576.96 546.07 491.60 435.83 407 .7 8404.66Figure 6.5. Visible spectral lines of metcury (Hg).

typical Iine spectra of mercury at visiblewavelengths.Some color bands are discrete while othersafe continuous. An atc soufce or a g sdischarge emits a discrete spectrum. That is,only certain wavelengths will appear, as bright

color lines are present. Meanwhile, af,incandescent solid such as a lamp filament

produces a continuous spectrum. That is, acontinuous band of colots with gradual shadingfrom short wavelength (violet) to the longwavelength (red).

m=1

Figure 6.4. Illustmtion of an emission spectrum showing the fitst and second ordet difftaction pattetnsat bottr sides of the direct image (principal maxima).

oBJECTTVESTo familiarize the students with the use of grating/prism spectrometer.To calibrate the spectrometer properly and to determine experimentally the gating constant, D.

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PhFto 7l-1 6- crlibrrin d*c rycs-


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Name: Date Performed:Date Submitted:

Section:

Partners:

Instructor:

A. Theoretical Grating ConstantDirect Image position:

Result:Grating Constant, Dexperimental :

DATA SUMMARYSpectrometer calibration: In calibrating your spectrometer, remember that the gratinB is placed on rheholder such that your reference spectral line of the Hg source has equal angles *h"n the Ller.op" i,rotated either rowards the left or right of the "straight-ahead,, image of the slit.CALIBRATION DATA 6c DETERMINATION oF THE GRATING CONSTANT D

Mercury light sourceOrder, m:

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. Theoretical Grating Constant:

Direct Image position:

Result:Grating Constant, D*pcrimtntet :

C. Theoretical Grating Constant:

Direct Image position:

Result:Grating Constant, Dexperimentel :

Mercury light source

Mercury light sourceOrder, m:

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phva;.71 1 6. calibration ofthe spectrometer

1. \Vhy do spectral lines appear on both directions, clochxrise (CW) and counterclochrise (CCW), fromthe "straight-ahead" image of the slit?

2. Compare the expedmental value of the Grating constant uzrth the Sating spacing of the difftactiongaang used. Explain similarity/difference.

3. Explain how the grating constant affects the observed spectral lines. Illustrate.



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SAMP.IJ CALCUI-ATIONS

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INTRODUCTIONThis experiment aims to coffelate the

observed emission spectra of several elementsto their energy levels.The hy&ogen atom is studied with the aidof the Bohr model. This semi-classical modelwas developed by Neils Bohr to explain thespectra emitted by hydrogen aroms. Accordingto this model,'the electron of a hydrogen atommoves in a circular orbit under the influence ofthe Coulomb attraction to the positive nucleus.The total energy of the electron is given by

mkzeo Zz FF. =-""-- - --Z'"*, n=1.,2,3....Q.1)n zhz flz - ttThe energies En (Z=1) are the allowedquantized energy levels for the hydrogen atom.The transitions bet'ween these eneigy levelsresult in the emission or absorption of photons.The_energy level diagram for hydrogenlhowingthe first few transitions id depicted in figure 7.1.For illustration, let us suppose that an il.ct ondrops from the second excited state (n=3) tothe firct excited state (n-2), then the electron

would lose energy totaling Es - Ez and isconverted to a photon whose energy is

whete h is the wavelength of theelectromagnetic wave associated with thephoton. Thus, the wavelength of the emittedradiation is

Ee - Ez =+,

*="(; il;="(i;)

(7.2)

Q.3)where F is the Rydberg's constant.For any transition from energy level n = ni

to any lowet energy level n = fl1, the wavelengthof the spectral line is(7.4)

Equation [.a) is known as the Rydberg-Ritzformula, where n, and nr are integers and R isthe Rydberg constatlt. R is known to be thesame for all spectral series of the same elementbut may vary slightly from element to element.For hydrogen, R=1.096776 x 107 m-l.Since the allowed energies arc quanttzed, we

n@43)

E., eV0.00-0.85-" -1.51Paschen series-3.40Balmer series

Lymann sedes -13.6

Natibnal Iustitute of Physics, UP DilimanFigure 7.1. The allowed orbits of


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Physics 73.1 7. spectrum of hydrogen and other elemetrtal vapo$

OBJECTTVES:To correlate the observed emission spectra to the energy levels of hydrogen.To experimentally determine the Rydberg constant for different elemental vapors.To be able to determine an unknown elemental vapor from its emission spectra.

METHODOLOGYA. MATERIALS1. diffraction grating Spectrometer

mercury discharge tube for calibrationhydrogen , and other elemental vaporshigh voltage power supply

expect that the wavelengths of the emittedphotons be likewise quantized as is observedfrom its line spectrum.

In this experiment, we will get the emissionspectra of several elements using gratingspectrometers. 'We will then correlate thesespectral lines to their transition energies, and in

B. PROCEDURE1. Calibration of the diffraction gratingspectrometer. Calibrate your spectrometerusing the technique you learned from theprevious experiment. Use the same diffractiongrating in the previous experiment so you do nothave to measure its grating constant again.

NOTE: Once the spectrometer is calibrated,tighten the screw that controls the grating holdermotion and do not move it' again. If this ismoved, the spectrometer must be calibratedagain.

2. Replace the Hg source used in calibrating yourspectrometer with a hydrogen discharge tube.Measure the angles right and left at which youfind the first and second order hydrogenspectnrm lines. Record your data.

the process compute for the Rydberg constartsof the given elements.

Once the technique of obtaining andquantifying the observed line spectrum isestablished, we will now try to identify anunknown gas discharge tube. Take note that theline spectra is unique for each atomic gas.

2.3.4.5.

Determine the wavelengths (includinguncertainties) present in this spectrum andcompare with the theoretical values. Identify theelectron transitions (energy levels involved)which give rise to the spectral lines seen, anddetermine the energy differences between theselevels using your experimental data. Finally,compute a value of the Rydberg constant,fromyour data, with uncertainty, and compare withthe theoretical value.3. Replace the hydrogen vapor tube with anotherelemental vapor. Be sure not to rnove anycomponent of the spectrometer. Otherwise, youhave to calibrate your setup again as discussed instep 1. Then repeat step 3. Do this again foranother vapor tube. Thus, every group musthave at least three data samples.

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Physics 73.1 7. spectrum of hydrogen and other elernental vaposWAYELENGTHS OF PRINCIPAL LINES OF EMISSION SPECTRA

Heliuml7avelength, A Color

7065A Red6678 Red5876 Yellow5016 Green4922 Blue-green471,3 Blue4471 Blue4387 Blue41,21 Violet4026 Violet

NeonWavelength, A Color

54514 Green5435 Green5852 Yellow5941 Yellow5945 Yellow6046 Red61,20 Red61,43 Red6266 Red6294 Red6328 Red

MercuryWavelength, A Color

5791A Yellow5770 Yellow5461 Green491,6 Blue-green4358 Blue4078 Violet4046 Violet

HydrogenWavelength, A Color

65634 Red4861 Blue-gteen4340 Blue41.02 Violet3970 Violet



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Physics 73.1 7. spectrum of hy&ogen and other elemeatal vapors

Draw the obserued spectral lines and the calculated wavelength:

Spectral lines of

Ttble7.2. Determination of the line spectra ofGrating constant: Direct Image Position:.g1:aRtrs; 1t:l$i=:ll!:13.-il!L,1f iW

:.':"'gf,-.'1::f iii$Li.W^iHi

1

Nationel Institute of Physics, UP Diliman


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Physics 73.1 7. spectrum of hvdroeen and other elemental vaoors

Draw the observed qpectral lines and the cdculated wavelength:

Natioaal Institute of Physics, UP Diliman


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Physics 73.1 7. spectrum of hydrogen and other elemental vaporsGrating constant:

Table 7.3. Detrrnination of the line spectra ofDirea Image Position:

LiJ:

I

2

Draw the observed spectrd lines and the calculated wavelength:

Figure 3.

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Physics 73.1 7. spectrum of hy&oeea atrd other elemmtal vaoorsTable 7.4. Determination of the line qpectra of the unknown source.

Grating constant:

Draw the obseryed qpectral lines and the cdculatedwavclength:

Figure 4. Spectral lines of unknown source.

The source is

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Phvsics 73.1 7, spectrum of hy&ogen and other elemental vpc

Determination of the Rydberg constant

Hydrogen

Otherelements

uo,| ^ (; *)

A

t/n? - t/nl+ i-+l -ii+1 t-i-+j- tr-1- j- i-j r+ r-'.1-'l T]TT1-+#j.i-ii ++ tl-'l- + i- 1-liiiiIi-l -i i:i.i1-l i-) t-T-t'-r-i+i"i -t--i-1 -t-i f-i t. iii .i.lli :i-+-t-i-l-i. +]-+-ff-i-1 I :I .r--i--L1"1-+ -t^ i.,t.i-l-.i. Il_ f-i i'1-i l- jj .i-!.i--i--i i

I i-t-ifi l-j .t-j.i:ili-iii -i-i I tt,-i i i l- r-l-j-f -i--Li- -i-..i-r-.1--i- i-L-f -f ri :'1.1 Il-rl jti!)I I i-t' iiri l- _i 1j i1iI+1 r-i -+.'T^ I.l f-t'-f-i- a-t-l-r i- 1- -i'{'-t. t- jt il+ij i: + i-*l--i-l -L Il-iii-i-"j-"i-1 - -i +-' r-i i-i-l- r-I i+-r i-f i {-'1- i11 -l-il-l-l Ltl.-r-L-!-Li-l i-] J i-r-j-rli-f'f-i-1 t- f[ii t- -i -ii-+ iIIlr) -f{" :i:t.i-lI :f-1 -+.I j-ii_t-1_l_.tl -i+-it -t-.l- it +ii-i.i i-+"li ''I fT i--1--tsfjii-i1 irl-l ai!i-li-i.i i t1' it t.l.i--t-i- r-t-i t': i i-'r1-l T i-r-i; ji- irl- l-. i t'ir-ii-i +.:-1"-+--1"'*i* -1 II + i-i-t-r-iil l- il+ "l- *i.1--i 1i-i-+ ++ir.i-ifti1-i- ri -r.+-+-i-+1-l l-+" 'j- 1-J- r+ .t+ ! l-t+1-+i-i-i-i l-1 l-+i-+-r--l-j-+ i+; +-t I f-fi--i-it -t-1 + j-r_'l +-' i.i i+- .* f+-;-r i J-i-+,- ".i-i -J!-1- ,i1, irit-i -rt-i_1_f_t ii f-r-Fa'-i-Fl-t-1-i-1 i. J. -Lr-i-1-1-1 - ++ifii_irt-r-F+ i--l-i-f-iljlii

j:Ir-:1_iIi_-i-+-i i- 111 + r--l-++fii l,l Ll.,i_i,r _Lt-i-i-r r-i] il ]-ii ++i fj ii -t-t-l -f -l- ii-ti + t-t -;-j j r.i-i r.+-t i- -f-.j- .i:i i-i i-i "-i. i-i: ,;i" i-i+ti-+I -i r'r- irlr++r-i- l-t ), :.ir'ti r r-1-i- +-1 i 'l-f

;!1.1-ifIr- l-1-f r- ),-1 -1-rt.-1 11' r-+ r-j Il i:i:Lil1t-j-l J, ii 1.t-rl- 1- t-i t_+f Ii I +1-+-r

I

I ll i+ i|l.lri. fl t-ii-t-1 Ij l.j l"-i i-i t--1-f-i-+-1 i-i-l-r :_ 1-l_

iii-it-j-l- l-.r- t- 1...1-

-f-i-r-i.+ i-i-il-1-]-t--1-i-r1-i i++i-+-1 +-i-"J-j-j-

:i:1l-+ l-.l- f

r1-4-

!-f ri

-Lt-i-t-..i-j-l-1,l--t -Ll-l--i-t-r-1t"i

fil.i '1- l-Llii.fr.i 1 ."J-ltJ.i + i--'.-i i i i-l-i-i-i -t; i-i ir_i t_i'iri ii i i-iaf_ T_r_i-i-f-i i'iiit I-t i.i iiii r1L+i r i-i-t-i-1 -1. -i -j--i-j.i i T +-l-ii .1, illl-t i-r-tf-i- f-i--i-l - I -1"I I 1-f -,-t il-r- Ii-r-i J- i1i-:--ii- -.1---t--a IIj-li-tl- |-i-+ l.-i-ia'1 i 'J i 1-+r_i _r Iiii-ri 1-r-1l,l:i l-i: i-+i-l-.1'-i

.J-.i-i-.i.1il l-1it -,ilii1-j-1-t-j j'1 r-l--r r -j-r il l

i-ii-il-r l- I "j-i-J -t-l-lr lr.i.il 1 1-1 i',,i11l-r t. r--j-1-i-j-t.l I t--i-.1 i i r-lr-i't',i.,-i -i:i:i ..j-'i-"1-+-f+ + I,-r-+r 'i- ii il-i-if.L +.i--t--i-i r t'l''i-i ir- -i-l r iiiii, -i--J--1-'1. l-i ij.l:* i-i-j-i-';'t'r ',-ii,i-:iif rtl_ i_f t'..i- i-l-.1- i -r.i ,ii i r-i'i I -l-l'r t_i_t_ i i-i .t- '1 -i-i r-I i f_'_1 il.i ii-i -i r +iiilrl ri-fit. i-l l_ii i'i- i-i-i i-it i++-i-F L,-l-1-i-\ I,i-Itt-t+-i- -f-F t.l i.j,l_t _f +1--i-f-i -1- T' "j- r^if-i i t'li.l-1_i-l- i- 1 i-i.j:i-il:. .i-j..j-j-r-l-+l- l-j-{-;-i i-l-i ir;- :i-i

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Phvsics 73.1

QUESTIONS1' Why shoutd the granng be norrnal to the-light coming from the collimator? How does the gratingequation (equation 6.2) change? Dtaw adtagrarnto supportyour calculations.

Compare the results (percenage difference) of the first order wavelengths to the second order.Should these wavelengths be the same? Why? \flhy no0

3. How does the Rydberg constaotdifferences?:'

for each gas? Can you for their



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SAMPLE CALCULATIONS

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. 7. spectrurn ofhydlogen and other elemental vapos

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INTRODUCTIONAbsolption spectroscopy is among theoldest of the fields of scientific specialization3.Isaac Newton is the best known eailyinvestigator of the spectrum back in the firstyears of the eighteenth century. A few yearslater, Bouger observed the change in intensity ofthe beam of light as it passes through anabsorbing medium of different thickness.However, it was not until the nineteenthcentury that \X/.H. Wollaston and J. Fraunhofer,separately observed spectral lines containingonly one color. It is also at this time that Beerpublished his observations on the dependenceof transmitted light on the concentration of theabsorbing species.Bunsen and Kirchhoff developed th; firstpractical spectroscope (similar to the ones weare using) in the middle of the nineteenthcentury. They showed that this technique couldbe used as a means of qualitative chemicalanalysis. They have discovered several elementsand demonstrate the presence of knownelements in the sun.When a ny of Jight passes a translucentmateri^\, it loses some of its original intensity.The attenuation of the intensiry of light is pardy

because of scattering by dirt or cloudiness, orreflected or tefracted by the surface at itsentrance and exit, and pardy because of theabsolption of the light by the matedal.Absolption spectoscopy is concerned withdetermining the relationship between thisattenuation due to absolption as l-ight passesthrough the material and the wavelength, orfrequency of the incident light.l

The study of the light absorption propertiesof a matertal has three objectives2: (1) to learnwhich wavelengths the material absorb; (2) toknow how much light is absorbed; and (3) togain knowledge on why the Iight is absorbed bythe material. In this experiment, we will bedealing with the first and third objectives only.The first objective gives us a "fingerprint" for aqualitative analysis of the material while thethird objective seeks to understand theabsorption in terms of the atoms and moleculesresponsible for absorption. Although aquantitative analysis would not be performed inthis experiment, a good insight in theabsolption of light by materials can be obtainedwith the two obiectives in mind. ,, l,l a-t ,' ea4tu'O). t. "fa alle7A w- @ .k Kll"01. f Crn

METHoDoLocy ,,*.rlr1r,'' t"-- :l f"u* 7'i /"A. MATERTALS \ prr, f ,ud.t/ ;'ol,.tYou need the following items for this experiment. Ask assistance from yorir ihstructor.Incandescent light sourceHigh voltage power supply Grating with a known grating constant /o Spectrometer

-'>,q"CO

'1\ ctTlab) |D/Connecting wires (preferably ailtgator clips) lGrating with a known grating coqqtant /

.BJECTI'ESrich wavereneths a ,' ?' tt Y 4\@" ffi*"','* It- ., c' 'c+ u'-To determine which "rgg:, gilr.'|, material absorbs. / r i lTo knowwhy the ,aidmrte.ial rbsorbs the wavelengths. 0C? Flrfuf ffud -

,l

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Physics 73.1 8, visual absorption spectroscopyName: Date Performed:

Date Submitted:

Section:

Table 8.1. 'S(avelenEhs Absorbed by Different Dyes

Partners:

Instructor:

DATA SUMMARY

Grating constant, D

Dye sample: Light Source RangeDirect Image Position:

Draw the observed spectrum and indicate the calculated wavelengths.

Figure 1. Spectrum



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Physics 73.1 8. visual absorption spectroscoDyDye sample: Light Source Range

Direct Image Position:

Draw the observed spectrum and indicate the cdculated wavelengths.

Figure 2. Spectrum

Dye sample: Light Source RangeDirect Image Position:

Draw the observed spectrum and indicate the calculated wavelengths.

Figure 3.


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TABII,2. COMPARISON VTITI LITERATURE VALUES.



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Physics73.1 , , , Q, visual alsorPtion sPectroscqyQUESTIONS1. \07hat are the advantages in using the visual specuoscopic method over other methods todetermine the absorption wavelengths of materids? the disadvantages?

Describe the effect of the different dyes on the spectrum of the Iight incident on it. Would lightbehave uniformly with different dyes? Why or why not?

3. What is the origin of the dark/darker bands (compared to the blank solution spectrum) in thespectrum of thJdyes? What do these bands correspond to? Will different dyes have the sameregion where one can locate these dark/darker bands?

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Physics 73.1 8. visual atrsomtion mectmcm

5. Consider a solution of chlorophyll. Draw and describe how its spectrum will look like.



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Phvsics 73.1 8' visual absorption spectroscopyCALCULATIONS

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physics73.1 laboratory manual

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