竞争市场上的企业曼昆经济学原理第七.pptx
What is a Competitive Market?Competitive marketPerfectly competitive marketMarket with many buyers and sellersTrading identical productsEach buyer and seller is a price takerFirms can freely enter or exit the market1第1页/共33页What is a Competitive Market?Firm in a competitive marketTries to maximize profit ProfitTotal revenue minus total costTotal revenue,TR=P QPrice times quantity Proportional to the amount of output2第2页/共33页What is a Competitive Market?Average revenue,AR=TR/QTotal revenue divided by the quantity soldMarginal revenue,MR=TR/QChange in total revenue from an additional unit soldFor competitive firmsAR=PMR=P3第3页/共33页Table 14Total,Average,and Marginal Revenue for a Competitive Firm第4页/共33页Profit MaximizationMaximize profitProduce quantity where total revenue minus total cost is greatestCompare marginal revenue with marginal costIf MR MC:increase productionIf MR MC,firm should increase outputIf MC MR,firm should decrease outputIf MR=MC,profit-maximizing level of outputMarginal-cost curveDetermines the quantity of the good the firm is willing to supply at any priceIs the supply curve9第9页/共33页Figure 210Marginal Cost as the Competitive Firms Supply CurvePrice An increase in the price from P1 to P2 leads to an increase in the firms profit-maximizing quantity from Q1 to Q2.Because the marginal-cost curve shows the quantity supplied by the firm at any given price,it is the firms supply curve.Quantity 0ATCAVCMCP1P2Q2Q1第10页/共33页Profit MaximizationShutdownShort-run decision not to produce anythingDuring a specific period of timeBecause of current market conditionsFirm still has to pay fixed costsExitLong-run decision to leave the marketFirm doesnt have to pay any costs11第11页/共33页Profit MaximizationThe firms short-run decision to shut downTR=total revenueVC=variable costsFirms decision:Shut down if TR VC(P AVC,.2.butshuts downif PAVC.第13页/共33页Profit MaximizationSunk costA cost that has already been committed and cannot be recoveredShould be ignored when making decisions“Dont cry over spilt milk”“Let bygones be bygones”In the short run,fixed costs are sunk costs 14第14页/共33页Near-empty restaurants&off-season miniature golfRestaurant stay open for lunch?Fixed costsNot relevantAre sunk costs in short runVariable costs relevantShut down if revenue from lunch variable costs15Staying open can be profitable,even with many tables empty.第15页/共33页Near-empty restaurants&off-season miniature golfOperator of a miniature-golf courseIgnore fixed costsShut down if Revenue variable costs16第16页/共33页Profit MaximizationFirms long-run decisionExit the market if Total revenue total costs;TR TCSame as:P total costs;TR TCSame as:P ATCCompetitive firms long-run supply curveThe portion of its marginal-cost curve that lies above average total cost17第17页/共33页Figure 418The Competitive Firms Long-Run Supply CurveCostsIn the long run,the competitive firms supply curve is its marginal-costcurve(MC)above average total cost(ATC).If the price falls below average total cost,the firm is better off exiting the market.Quantity 0MC1.In the long run,the firm produces on the MC curve if PATC,.2.but exits if P ATCProfit=TR TC=(P ATC)QIf P AVC:supply curve is MC curveMarket supplyAdd up quantity supplied by each firm21第21页/共33页Figure 622Short-Run Market SupplyPriceIn the short run,the number of firms in the market is fixed.As a result,the market supply curve,shown in panel(b),reflects the individual firms marginal-cost curves,shown in panel(a).Here,in a market of 1,000 firms,the quantity of output supplied to the market is 1,000 times the quantity supplied by each firm.Quantity(firm)0(a)Individual firm supplyMC100$2.00PriceQuantity(market)0(b)Market supply2001.00Supply100,000$2.00200,0001.00第22页/共33页Supply CurveLong runFirms can enter and exit the marketIf P ATC,firms make positive profitNew firms enter the marketIf P ATC positive economic profit27第27页/共33页Supply CurvePositive economic profit in short runLong run firms enter the marketShort run supply curve shifts rightPrice decreases back to minimum ATCQuantity increases Because there are more firms in the marketEfficient scale28第28页/共33页Figure 829An Increase in Demand in the Short Run and Long Run(a)PricePriceThe market starts in a long-run equilibrium,shown as point A in panel(a).In this equilibrium,each firm makes zero profit,and the price equals the minimum average total cost.Quantity(market)0MarketQuantity(firm)0FirmATCMC(a)Initial ConditionShort-run supply,S1Demand,D1Q1P1Long-runsupplyP1A1.A market begins inlong-run equilibrium2.with the firmearning zero profit.第29页/共33页Figure 830An Increase in Demand in the Short Run and Long Run(b)PricePricePanel(b)shows what happens in the short run when demand rises from D1 to D2.The equilibrium goes from point A to point B,price rises from P1 to P2,and the quantity sold in the market rises from Q1 to Q2.Because price now exceeds average total cost,each firm now makes a profit,which over time encourages new firms to enter the market.Quantity(market)0MarketQuantity(firm)0Firm(b)Short-Run ResponseS1D1Q1P1Long-runsupplyP1A3.But then an increase in demand raises the price4.leading toshort-run profits.D2BQ2P2P2MCATC第30页/共33页Figure 831An Increase in Demand in the Short Run and Long Run(c)PricePriceThis entry shifts the short-run supply curve to the right from S1 to S2,as shown in panel(c).In the new long-run equilibrium,point C,price has returned to P1 but the quantity sold has increased to Q3.Profits are again zero,and price is back to the minimum of average total cost,but the market has more firms to satisfy the greater demand.Quantity(market)0MarketQuantity(firm)0Firm(c)Long-Run ResponseS1D1Q1AD2BQ2P2MCATC5.When profits induce entry,supply increases and the price falls,6.restoring long-run equilibrium.S2CQ3P1P1Long-runsupply第31页/共33页Supply CurveLong-run supply curve might slope upward Some resource used in production may be available only in limited quantitiesIncrease in quantity supplied increase in costs increase in priceFirms may have different costsSome firms earn profit even in the long runLong-run supply curveMore elastic than short-run supply curve32第32页/共33页
