曼昆经济学 宏观经济学 第五版 教师参考手册 chap04.docx

曼昆经济学 宏观经济学 第五版 教师参考手册 chap04.docx

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曼昆经济学宏观经济学第五版教师参考手册chap04

4

THEMARKETFORCESOFSUPPLYANDDEMAND

WHAT’SNEW:

Thetextdiscussionofthedeterminantsofdemandandsupplynowemphasizesthespecialroleofpriceandthefactthatachangeinpricecausesamovementalongagivencurvewhileachangeintheotherdeterminantsresultsinashiftofthecurve.Theterms“shortage”and“surplus”arenowusedinsteadof“excessdemand”and“excesssupply.”Anewtablehasbeenaddedthatsummarizeswhathappenstoequilibriumpriceandquantitywhensupplyanddemandshift.AnIntheNewssegmenthasalsobeenaddedon“MotherNatureShiftstheSupplyCurve.”

LEARNINGOBJECTIVES:

Bytheendofthischapter,studentsshouldunderstand:

Øwhatacompetitivemarketis.

Øwhatdeterminesthedemandforagoodinacompetitivemarket.

Øwhatdeterminesthesupplyofagoodinacompetitivemarket.

Øhowsupplyanddemandtogethersetthepriceofagoodandthequantitysold.

Øthekeyroleofpricesinallocatingscarceresourcesinmarketeconomies.

KEYPOINTS:

1.Economistsusethemodelofsupplyanddemandtoanalyzecompetitivemarkets.Inacompetitivemarket,therearemanybuyersandsellers,eachofwhomhaslittleornoinfluenceonthemarketprice.

2.Thedemandcurveshowshowthequantityofagooddemandeddependsontheprice.Accordingtothelawofdemand,asthepriceofagoodfalls,thequantitydemandedrises.Therefore,thedemandcurveslopesdownward.

3.Inadditiontoprice,otherdeterminantsofthequantitydemandedincludeincome,tastes,expectations,andthepricesofsubstitutesandcomplements.Ifoneoftheseotherdeterminantschanges,thedemandcurveshifts.

4.Thesupplycurveshowshowthequantityofagoodsupplieddependsontheprice.Accordingtothelawofsupply,asthepriceofagoodrises,thequantitysuppliedrises.Therefore,thesupplycurveslopesupward.

5.Inadditiontoprice,otherdeterminantsofthequantitysuppliedincludeinputprices,technology,andexpectations.Ifoneoftheseotherdeterminantschanges,thesupplycurveshifts.

6.Theintersectionofthesupplyanddemandcurvesdeterminesthemarketequilibrium.Attheequilibriumprice,thequantitydemandedequalsthequantitysupplied.

7.Thebehaviorofbuyersandsellersnaturallydrivesmarketstowardtheirequilibrium.Whenthemarketpriceisabovetheequilibriumprice,thereisasurplusofthegood,whichcausesthemarketpricetofall.Whenthemarketpriceisbelowtheequilibriumprice,thereisashortage,whichcausesthemarketpricetorise.

8.Toanalyzehowanyeventinfluencesamarket,weusethesupply-and-demanddiagramtoexaminehowtheeventaffectsequilibriumpriceandquantity.Todothiswefollowthreesteps.First,wedecidewhethertheeventshiftsthesupplycurveorthedemandcurve.Second,wedecidewhichdirectionthecurveshifts.Third,wecomparethenewequilibriumwiththeoldequilibrium.

9.Inmarketeconomies,pricesarethesignalsthatguideeconomicdecisionsandtherebyallocatescarceresources.Foreverygoodintheeconomy,thepriceensuresthatsupplyanddemandareinbalance.Theequilibriumpricethendetermineshowmuchofthegoodbuyerschoosetopurchaseandhowmuchsellerschoosetoproduce.

CHAPTEROUTLINE:

I.MarketsandCompetition

A.DefinitionofMarket:

agroupofbuyersandsellersofaparticulargoodorservice.

Youmaywanttoprovidestudentswithexamplesofmarketsotherthanthetraditionalretailstoreorthestockmarket.Theseincludetheclassifiedadvertisingsectionofanewspaper,thecollege“careerservices”departmentthroughwhichtheycanlookforemploymentupongraduation,orthemarketformarijuanaonacollegecampus.Besuretolistthegoodorservicebeingsold,thebuyers,andthesellersineachexample.

B.DefinitionofCompetitiveMarket:

amarketinwhichtherearemanybuyersandmanysellerssothateachhasanegligibleimpactonthemarketprice.

Studentsmayfindthenameforthistypeofmarketmisleading.Youwillhavetopointoutthatfirmsinacompetitivemarketdonotfacehead-to-headrivalryasinsportscompetitions.

C.Competition:

PerfectandOtherwise

1.Characteristicsofaperfectlycompetitivemarket:

a.Thegoodsbeingofferedforsaleareallthesame.

b.Thebuyersandsellersaresonumerousthatnonecaninfluencethemarketprice.

2.Becausebuyersandsellersmustacceptthemarketpriceasgiven,theyareoftencalled“pricetakers.”

3.Agriculturalmarketsprovidegoodexamplesofperfectcompetition.

4.Amarketwithonlyoneselleriscalledamonopolymarket.

5.Amarketwithonlyafewsellersiscalledanoligopoly.

6.Amarketwithalargenumberofsellers,eachsellingaproductthatisslightlydifferentfromitscompetitors’products,iscalledmonopolisticcompetition.

D.Wewillstartbyassumingperfectcompetition.

II.Demand

A.DefinitionofQuantityDemanded:

theamountofagoodthatbuyersarewillingandabletopurchase.

B.WhatDeterminestheQuantityanIndividualDemands?

1.Price

a.Quantitydemandedisnegativelyrelatedtoprice.Thisimpliesthatthedemandcurveisdownward-sloping.

b.DefinitionofLawofDemand:

theclaimthat,otherthingsbeingequal,thequantitydemandedofagoodfallswhenthepriceofthegoodrises.

Makesurethatyouexplainthat,whenwediscusstherelationshipbetweenquantitydemandedandprice,weholdallothervariablesconstant.Youwillneedtoemphasizethismorethanoncetoensurethatstudentsunderstandwhyachangeinpriceleadstoamovementalongthedemandcurve.

2.Income

a.Therelationshipbetweenincomeandquantitydemandeddependsonwhattypeofgoodtheproductis.

b.DefinitionofNormalGood:

agoodforwhich,otherthingsequal,anincreaseinincomeleadstoanincreaseindemand.

c.DefinitionofInferiorGood:

agoodforwhich,otherthingsequal,anincreaseinincomeleadstoadecreaseindemand.

Becareful!

Studentsoftenconfuseinferiorgoodswithwhateconomistscall“bads.”Onewaytodifferentiatethemistoaskstudentswhethertheywouldeverbewillingtopayforsuchthingsaspollutionorgarbage.

3.PricesofRelatedGoods

a.DefinitionofSubstitutes:

twogoodsforwhichanincreaseinthepriceofonegoodleadstoanincreaseinthedemandfortheothergood.

b.DefinitionofComplements:

twogoodsforwhichanincreaseinthepriceofonegoodleadstoadecreaseinthedemandfortheothergood.

4.Tastes

5.Expectations

a.Thiscouldincludeexpectationsoffutureincomeorexpectationsoffuturepricechanges.

C.TheDemandScheduleandtheDemandCurve

1.DefinitionofDemandSchedule:

atablethatshowstherelationshipbetweenthepriceofagoodandthequantitydemanded.

Table4-1

PriceofIceCreamCone

QuantityofConesDemanded

$0.00

12

0.50

10

1.00

8

1.50

6

2.00

4

2.50

2

3.00

0

Whenyoudrawthedemandcurveforthefirsttime,takethetimetoploteachofthepointsfromthedemandschedule.Thisway,studentswhohavedifficultywithgraphscanseetherelationshipbetweenthedemandscheduleandthedemandcurve.Thisisagoodtimetoseeifstudentsunderstandthe（x,y）coordinatesystem.

2.DefinitionofDemandCurve:

agraphoftherelationshipbetweenthepriceofagoodandthequantitydemanded.

Figure4-1

Price

3.00

2.50

2.00

1.50

1.00

0.50

2

4

6

8

10

12

IceCreamCones

ALTERNATIVECLASSROOMEXAMPLE:

Hereisademandschedulefor#2leadpencils:

Price

QuantityDemanded

.05

1000

.10

800

.15

600

.20

400

.25

200

D.CeterisParibus

1.Whenademandcurveisdrawn,everythingbutpriceandquantitydemandedisheldconstant.

2.Economistsusetheterm“ceterisparibus”topointoutthatallotherrelevantvariablesareassumedfixed.

3.DefinitionofCeterisParibus:

aLatinphrase,translatedas“otherthingsbeingequal,”usedasareminderthatallvariablesotherthantheonesbeingstudiedareassumedtobeconstant.

E.MarketDemandVersusIndividualDemand

1.Themarketdemandisthesumofalloftheindividualdemandsforaparticulargoodorservice.

2.Thedemandcurvesaresummedhorizontally—meaningthatthequantitiesdemandedareaddedupforeachlevelofprice.

Figure4-2

Table4-2

3.Themarketdemandcurveshowshowthetotalquantitydemandedofagoodvarieswiththepriceofthegood.

F.ShiftsintheDemandCurve

Studentshaveadifficulttimeunderstandingthedifferencebetweenachangeinprice（whichcausesamovementalongthedemandcurve）andachangeinanotherdeterminant（whichshiftsthedemandcurve）.Youwillhavetoemphasizewhatismeantby“changeinquantitydemanded”and“changeindemand”severaltimesusingdifferentexamples.TheCaseStudyonsmokingwillhelptoexplainthisdifferenceaswell.

Figure4-3

1.Whenanydeterminantofdemandchanges（otherthanprice）,thedemandcurvewillshift.

2.Anincreaseindemandcanberepresentedbyashiftofthedemandcurvetotheright.

3.Adecreaseindemandcanberepresentedbyashiftofthedemandcurvetotheleft.

4.Table4-3liststhevariablesthatinfluencequantitydemandedandhowachangeineachvariableaffectsthedemandcurve.

Table4-3

Itwouldbeagoodideatoworkthroughanexamplechangingeachofthesevariablesindividually.Studentswillbenefitfromthediscussionaswellasthepracticedrawingthegraphs.

G.CaseStudy:

TwoWaystoReducetheQuantityofSmokingDemanded

Figure4-4

1.Publicserviceannouncements,mandatoryhealthwarningsoncigarettepackages,andtheprohibitionofcigaretteadvertisingontelevisionarepoliciesdesignedtoreducethedemandforcigarettes（andshiftthedemandcurvetotheleft）.

2.Raisingthepriceofcigarettes