《微观经济学》清华大学课件 Ch15 Market Demand.ppt

ChapterFifteen MarketDemand FromIndividualtoMarketDemandFunctions Thinkofaneconomycontainingnconsumers denotedbyi 1 n Consumeri sordinarydemandfunctionforcommodityjis FromIndividualtoMarketDemandFunctions Whenallconsumersareprice takers themarketdemandfunctionforcommodityjis FromIndividualtoMarketDemandFunctions p1 p1 p1 20 15 35 p1 p1 p1 p1 p1 p1 The horizontalsum ofthedemandcurvesofindividualsAandB Elasticities Elasticitymeasuresthe sensitivity ofonevariablewithrespecttoanother TheelasticityofvariableXwithrespecttovariableYis Own PriceElasticityofDemand Q Whynotjustusetheslopeofademandcurvetomeasurethesensitivityofquantitydemandedtoachangeinacommodity sownprice A Becausethevalueofsensitivitythendependsuponthe arbitrary unitsofmeasurementusedforquantitydemanded ArcandPointElasticities An average own priceelasticityofdemandforcommodityioveranintervalofvaluesforpiisanarc elasticity usuallycomputedbyamid pointformula Elasticitycomputedforasinglevalueofpiisapointelasticity ArcOwn PriceElasticity pi Xi pi pi h pi h Whatisthe average own priceelasticityofdemandforpricesinanintervalcenteredonpi ArcOwn PriceElasticity pi Xi pi pi h pi h Whatisthe average own priceelasticityofdemandforpricesinanintervalcenteredonpi PointOwn PriceElasticity pi Xi pi pi h pi h Whatistheown priceelasticityofdemandinaverysmallintervalofpricescenteredonpi Ash 0 PointOwn PriceElasticity pi Xi pi Whatistheown priceelasticityofdemandinaverysmallintervalofpricescenteredonpi istheelasticityatthepoint PointOwn PriceElasticity E g Supposepi a bXi ThenXi a pi band Therefore PointOwn PriceElasticity pi Xi a pi a bXi a b a 2 a 2b PointOwn PriceElasticity pi Xi a pi a bXi a b a 2 a 2b own priceelastic own priceinelastic own priceunitelastic PointOwn PriceElasticity E g Then so PointOwn PriceElasticity pi Xi everywherealongthedemandcurve RevenueandOwn PriceElasticityofDemand Ifraisingacommodity spricecauseslittle alotof decreaseinquantitydemanded thensellers revenuesrise Henceown priceinelastic elastic demandcausessellers revenuestorise drop aspricerises RevenueandOwn PriceElasticityofDemand Sellers revenueis So RevenueandOwn PriceElasticityofDemand soif then andachangetopricedoesnotaltersellers revenue RevenueandOwn PriceElasticityofDemand butif then andapriceincreaseraisessellers revenue RevenueandOwn PriceElasticityofDemand Andif then andapriceincreasereducessellers revenue MarginalRevenueandOwn PriceElasticityofDemand Aseller smarginalrevenueistherateatwhichrevenuechangeswiththenumberofunitssoldbytheseller MarginalRevenueandOwn PriceElasticityofDemand p q denotestheseller sinversedemandfunction i e thepriceatwhichthesellercansellqunits Then so MarginalRevenueandOwn PriceElasticityofDemand and so MarginalRevenueandOwn PriceElasticityofDemand If then If then If then MarginalRevenueandOwn PriceElasticityofDemand Anexamplewithlinearinversedem