ap经济学第6次课竞争性市场

1、 2007 Thomson South-WesternWHAT IS A COMPETITIVE MARKET?什么是竞争性市场?A competitive market has many buyers and sellers trading identical products so that each buyer and seller is a price taker.竞争性市场拥有许多买者和卖者,他们所交易的是相同的产品,因此每一个买者和卖者都是价格的接受者.Buyers and sellers must accept the price determined by the market

2、.买者和卖者必须接受市场决定的价格.The Meaning of Competition竞争的涵义A perfectly competitive market has the following characteristics: 一个完全竞争的市场具有下列特征:There are many buyers and sellers in the market.市场上存在着许多买者和卖者The goods offered by the various sellers are largely the same.由各个不同的卖者所提供的商品在很大程度上是相同的。Firms can freely ente

3、r or exit the market.企业能够自由地进入和退出市场。The Meaning of Competition竞争的涵义As a result of its characteristics, the perfectly competitive market has the following es:作为其特征的结果，完全竞争市场具有下列结果：The actions of any single buyer or seller in the market have a negligible impact on the market price.市场上任何单一的买者或卖者对市场价格的影

4、响都是微不足道的。Each buyer and seller takes the market price as given. 每一个买者或卖者把市场价格都看作是给定的。The Revenue of a Competitive Firm竞争性企业的收益Total revenue for a firm is the selling price times the quantity sold.企业的总收益是销售价格乘出售的数量TR = (P Q) Total revenue is proportional to the amount of output.总收益与产出数量成比例The Revenue

5、 of a Competitive Firm竞争性企业的收益Average revenue tells us how much revenue a firm receives for the typical unit sold.平均收益告诉我们一个企业从销售的典型单位中获取多少收益Average revenue is total revenue divided by the quantity sold.平均收益是总收益除销售数量The Revenue of a Competitive Firm竞争性企业的收益In perfect competition, average revenue equ

6、als the price of the good.在完全竞争中，平均收益等于商品的价格。The Revenue of a Competitive Firm竞争性企业的收益Marginal revenue is the change in total revenue from an additional unit sold.边际收益是来自新增一单位销售的总收益变化MR =TR/QFor competitive firms, marginal revenue equals the price of the good.对于竞争性企业来说，边际收益等于商品的价格。Table 1 Total, Ave

7、rage, and Marginal Revenue for a Competitive FirmPROFIT MAXIMIZATION AND THE COMPETITIVE FIRMS SUPPLY CURVE利润最大化与竞争性企业的供给曲线The goal of a competitive firm is to maximize profit.竞争性企业的目标是使利润达到最大化This means that the firm will want to produce the quantity that maximizes the difference between total reve

8、nue and total cost.这意味着企业想要生产的数量能够使得总收益与总成本之间的差额达到最大化。Table 2 Profit Maximization: A Numerical Example表2：利润最大化-一个数字化范例The Marginal Cost-Curve and the Firms Supply Decision边际成本曲线与企业的供给决策Profit maximization occurs at the quantity where marginal revenue equals marginal cost.利润最大化出现在边际收益等于边际成本的数量上。When

9、MR MC, increase Q 当边际收益大于边际成本时，数量增加。When MR MC, decrease Q当边际收益小于边际成本时，数量减少。When MR = MC, profit is maximized.当边际收益等于边际成本时，利润达到最大化。Figure 1 Profit Maximization for a Competitive Firm图1：竞争性企业的利润最大化Quantity0CostsandRevenueMCATCAVCMC1Q1MC2Q2The firm maximizesprofit by producing the quantity at whichmar

10、ginal cost equalsmarginal revenue.QMAX P = MR1 = MR2 P = AR = MRIf the firm produces Q1, marginal cost is MC1.If the firm produces Q2, marginal cost is MC2.Suppose the market price is P.Figure 2 Marginal Cost as the Competitive Firms Supply Curve图2：作为竞争性企业供给曲线的边际成本Quantity0PriceMCATCAVCP1Q1P2Q2So, t

11、his section of thefirms MC curve isalso the firms supplycurve.As P increases, the firm will select its level of output along the MC curve.The Firms Short-Run Decision to Shut Down企业关闭的短期决策A shutdown refers to a short-run decision not to produce anything during a specific period of time because of cu

12、rrent market conditions.暂时关闭是指在某一特定时期内因为当时的市场条件而决定不生产任何东西的短期决策Exit refers to a long-run decision to leave the market.退出是指离开市场的长期决策The Firms Short-Run Decision to Shut Down企业关闭的短期决策The firm shuts down if the revenue it gets from producing is less than the variable cost of production.如果来自其生产的收益小于生产成本时

13、，企业会暂时关闭。Shut down if TR VCShut down if TR/Q VC/QShut down if P AVCFigure 3 The Competitive Firms Short-Run Supply Curve图3：竞争性企业的短期供给曲线MCQuantityATCAVC0CostsFirmshutsdown ifP AVC, firm will continue to produce in the short run.If P ATC, the firm will continue to produce at a profit.Spilt Milk and Ot

14、her Sunk CostsThe firm considers its sunk costs when deciding to exit, but ignores them when deciding whether to shut down.在决定退出时企业考虑其沉淀成本，但是在决定是否暂时关闭时可忽略沉淀成本。Sunk costs are costs that have already been committed and cannot be recovered.沉淀成本是已经投入并且无法挽回的成本The Firms Short-Run Decision to Shut Down企业关闭

15、的短期决策The portion of the marginal-cost curve that lies above average variable cost is the competitive firms short-run supply curve.边际成本曲线位于平均可变成本以上的部分是竞争性企业的短期供给曲线。The Firms Long-Run Decision to Exit or Enter a Market企业退出或者进入一个市场的长期决策In the long run, the firm exits if the revenue it would get from pr

16、oducing is less than its total cost.在长期中，如果企业从生产中获得的收益小于其总成本的话，它就退出。Exit if TR TCExit if TR/Q TC/QExit if P TCEnter if TR/Q TC/QEnter if P ATCFigure 4 The Competitive Firms Long-Run Supply Curve图4：竞争性市场的长期供给曲线MC = long-run SFirmexits ifP ATC Measuring Profit in Our Graph for the Competitive Firm在我们有

17、关竞争性企业的图中测度利润Profit = TR TCProfit = (TR/Q TC/Q) x QProfit = (P ATC) x QFigure 5 Profit as the Area between Price and Average Total Cost图5：价格与平均总成本之间的面积是利润A Firm with Profits 有利润的企业Quantity0PriceP = AR = MRATCMCPATCQ(profit-maximizing quantity)利润最大化数量ProfitFigure 5 Loss as the Area between Average To

18、tal Cost and Price 图5：平均总成本与价格之间的面积是亏损(b) A Firm with Losses 有亏损的企业Quantity0PriceATCMC(loss-minimizing quantity)亏损最小数量P = AR = MRPATCQLossTHE SUPPLY CURVE IN A COMPETITIVE MARKET竞争性市场中的供给曲线The competitive firms long-run supply curve is the portion of its marginal-cost curve that lies above average t

19、otal cost.竞争性企业的长期供给曲线是位于平均总成本曲线之上的边际成本曲线。THE SUPPLY CURVE IN A COMPETITIVE MARKET竞争性市场中的供给曲线Short-Run Supply Curve 短期供给曲线The portion of its marginal cost curve that lies above average variable cost. 边际成本曲线位于平均可变成本之上的部分Long-Run Supply Curve 长期供给曲线The marginal cost curve above the minimum point of it

20、s average total cost curve.边际成本曲线位于其平均总成本曲线的最低点之上THE SUPPLY CURVE IN A COMPETITIVE MARKET竞争性市场中的供给曲线Market supply equals the sum of the quantities supplied by the individual firms in the market. 市场供给等于市场中个别企业所供给的数量之总和The Short Run: Market Supply with a Fixed Number of Firms短期：企业数量固定的市场供给For any give

21、n price, each firm supplies a quantity of output so that its marginal cost equals price. 对于任何给定的价格，每一企业供给特定的产出数量。以便使其边际成本等于价格。The market supply curve reflects the individual firms marginal cost curves. 市场供给曲线反映出个别企业的边际成本曲线Figure 6 Short-Run Market Supply图6：短期市场供给Individual Firm Supply个别企业的供给Quantity

22、 (firm)0PriceMC1.00100$2.00200(b) Market Supply市场供给Quantity (market)0PriceSupply1.00100,000$2.00200,000If the industry has 1000 identical firms, then at each market price, industry output will be 1000 times larger than the representative firms output.如果该产业拥有一千家相同企业，该产业的产出将比代表性企业的产出大一千倍。The Long Run:

23、 Market Supply with Entry and Exit长期：有进入与退出的市场供给Firms will enter or exit the market until profit is driven to zero.企业将进入或退出市场直到利润趋向于零In the long run, price equals the minimum of average total cost.在长期中，价格等于平均总成本的最低点。The long-run market supply curve is horizontal at this price.长期市场供给曲线在此价格呈水平状Figure

24、7 Long-Run Market Supply图7：长期市场供给(a) Firms Zero-Profit ConditionQuantity (firm)0Price(b) Market SupplyQuantity (market)Price0P = minimumATCSupplyMCATCThe Long Run: Market Supply with Entry and Exit长期：有进入与退出的市场供给At the end of the process of entry and exit, firms that remain must be making zero econom

25、ic profit.在进入和退出过程结束时，留存的企业必定获得零经济利润。The process of entry and exit ends only when price and average total cost are driven to equality.只有在价格与平均总成本趋向相等时，进入和退出过程才会结束。Long-run equilibrium must have firms operating at their efficient scale.长期均衡必定使得企业在其有效规模水平上运行Why Do Competitive Firms Stay in Business If

26、 They Make Zero Profit?为什么竞争性企业在获得零利润时还要留存在其业务之中？Profit equals total revenue minus total cost.利润等于总收益减去总成本Total cost includes all the opportunity costs of the firm.总成本包括企业的所有机会成本In the zero-profit equilibrium, the firms revenue compensates the owners for the time and money they expend to keep the bu

27、siness going.在零利润均衡中，企业的收益补偿了所有者为了维持业务运行所花费的时间和金钱。A Shift in Demand in the Short Run and Long Run短期与长期中的需求变动An increase in demand raises price and quantity in the short run.在短期内，需求增加会提高价格和数量。Firms earn profits because price now exceeds average total cost.企业获得利润，因为目前价格超越了总成本。Figure 8 An Increase in D

28、emand in the Short Run and Long Run图8：短期与长期中的需求增加FirmInitial Condition 初始条件Quantity (firm)0PriceMarketQuantity (market)Price0DDemand, 1SShort-run supply, 1P1ATCLong-runsupplyP11QAMCA market begins in long run equilibrium. 在长期均衡中市场启动And firms earn zero profit.企业获得零利润Figure 8 An Increase in Demand in

29、the Short Run and Long Run图8：短期和长期中的需求增加MarketFirm(b) Short-Run Response 短期反应Quantity (firm)0PriceP1Quantity (market)Long-runsupplyPrice0D1D2P1S1P2Q1AQ2P2BATCMCAn increase in market demandraises price and output.The higher P encourages firms to produce moreand generates short-run profit.Figure 8 An

30、Increase in Demand in the Short Run and Long Run图8：短期与长期中的需求增加P1Firm(c) Long-Run Response 长期反应Quantity (firm)0PriceMCATCMarketQuantity (market)Price0P1P2Q1Q2Long-runsupplyBD1D2S1AS2Q3CProfits induce entry and market supply increases.利润引致进入和市场供给增加The increase in supply lowers market price.供给增加减低市场价格I

31、n the long run market price is restored, but market supply is greater.Why the Long-Run Supply Curve Might Slope Upward为什么长期供给曲线会向上倾斜？Some resources used in production may be available only in limited quantities.生产中使用的某些资源也许只能以有限的数量获得Firms may have different costs.企业也许具有不同的成本Marginal Firm 边际企业The mar

32、ginal firm is the firm that would exit the market if the price were any lower.边际企业是在价格降低时会退出市场的企业Because a competitive firm is a price taker, its revenue is proportional to the amount of output it produces.因为竞争性企业是价格接受者，它的收益是与其生产的数量成比例的。The price of the good equals both the firms average revenue and its marginal revenue.商品的价格等于企业的平均收益和它的边际收益To maximize