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1、CHAPTER 8 OUTLINE,8.1 Perfectly Competitive Markets 8.2 Profit Maximization 8.3 Marginal Revenue, Marginal Cost, and Profit Maximization 8.4 Choosing Output in the Short Run 8.5 The Competitive Firms Short-Run Supply Curve 8.6 The Short-Run Market Supply Curve 8.7 Choosing Output in the Long Run 8.8
2、 The Industrys Long-Run Supply Curve,PERFECTLY COMPETITIVE MARKETS,The model of perfect competition rests on three basic assumptions: (1) price taking, (2) product homogeneity, and (3) free entry and exit.,Price Taking,Because each individual firm sells a sufficiently small proportion of total marke
3、t output, its decisions have no impact on market price., price taker Firm that has no influence over market price and thus takes the price as given.,Product Homogeneity,When the products of all of the firms in a market are perfectly substitutable with one anotherthat is, when they are homogeneousno
4、firm can raise the price of its product above the price of other firms without losing most or all of its business.,PERFECTLY COMPETITIVE MARKETS,Free Entry and Exit, free entry (or exit) Condition under which there are no special costs that make it difficult for a firm to enter (or exit) an industry
5、.,When Is a Market Highly Competitive?,Because firms can implicitly or explicitly collude(或明或暗地串通)in setting prices, the presence of many firms is not sufficient for an industry to approximate perfect competition. Conversely, the presence of only a few firms in a market does not rule out competitive
6、 behavior.,股票市场是不是完全竞争,纽约证卷交易所的交易量约占上市公司股票总量的80% 纳斯达克（Nasdaq）（全国证卷经销商协会自动报价系统）是一个数千家未上市公司股票的电子交易系统，其股票是以及百家经纪商和经销商为基础进行的交易 纳斯达克经销商也曾暗中共谋操纵股价，1997年12月，曾对美林公司（Merrill Lynch&Co.）和花旗集团的索罗门史密斯巴尼公司进行10.3亿美元的罚款,PROFIT MAXIMIZATION,Do Firms Maximize Profit?,The assumption of profit maximization is frequentl
7、y used in microeconomics because it predicts business behavior reasonably accurately and avoids unnecessary analytical complications. For smaller firms managed by their owners, profit is likely to dominate almost all decisions. In larger firms, however, managers who make day-to-day decisions usually
8、 have little contact with the owners (i.e. the stockholders). In any case, firms that do not come close to maximizing profit are not likely to survive. Firms that do survive in competitive industries make long-run profit maximization one of their highest priorities.,Alternative Forms of Organization
9、, cooperative Association of businesses or people jointly owned and operated by members for mutual benefit.,Do Firms Maximize Profit?,追求利润是企业生存的必要条件。企业行为在短期内可能会偏离利润目标，但长期而言，在激烈竞争的市场上它就会被淘汰 一个补贴公共电视台的企业似乎看起来是有公益精神和利他主义的，但这一慈善行为可能正是该企业的长期经济利益之所在，因为它给企业及其产品创造了商誉。,MARGINAL REVENUE, MARGINAL COST, AND PR
10、OFIT MAXIMIZATION, profit Difference between total revenue and total cost.,(q) = R(q) C(q), marginal revenue Change in revenue resulting from a one-unit increase in output.,Profit Maximization in the Short Run,Figure 8.1,A firm chooses output q*, so that profit, the difference AB between revenue R a
11、nd cost C, is maximized. At that output, marginal revenue (the slope of the revenue curve) is equal to marginal cost (the slope of the cost curve).,/q = R/q C/q = 0,MR(q) = MC(q),利润最大化的条件,Max (q)=R(q)-C(q) 方程对q求导，令其值为0 d (q)/dq=d R(q)/dq-d C(q)/dq=0 d R(q)/dq= d C(q)/dq 利润最大时有：MR=MC,MARGINAL REVENUE
12、, MARGINAL COST, AND PROFIT MAXIMIZATION,Demand and Marginal Revenue for a Competitive Firm,Demand Curve Faced by a Competitive Firm,Figure 8.2,A competitive firm supplies only a small portion of the total output of all the firms in an industry. Therefore, the firm takes the market price of the prod
13、uct as given, choosing its output on the assumption that the price will be unaffected by the output choice. In (a) the demand curve facing the firm is perfectly elastic, even though the market demand curve in (b) is downward sloping.,MARGINAL REVENUE, MARGINAL COST, AND PROFIT MAXIMIZATION,The deman
14、d d curve facing an individual firm in a competitive market is both its average revenue curve and its marginal revenue curve. Along this demand curve, marginal revenue, average revenue, and price are all equal.,Profit Maximization by a Competitive Firm,MC(q) = MR = P,Demand and Marginal Revenue for
15、a Competitive Firm,CHOOSING OUTPUT IN THE SHORT RUN,Short-Run Profit Maximization by a Competitive Firm,Marginal revenue equals marginal cost at a point at which the marginal cost curve is rising.,Output Rule: If a firm is producing any output, it should produce at the level at which marginal revenu
16、e equals marginal cost.,CHOOSING OUTPUT IN THE SHORT RUN,The Short-Run Profit of a Competitive Firm,A Competitive Firm Making a Positive Profit,Figure 8.3,In the short run, the competitive firm maximizes its profit by choosing an output q* at which its marginal cost MC is equal to the price P (or marginal revenue MR) of its product. The profit of the firm is measured by the rectangle ABCD. Any change in output, whether lower at q1 or higher at q2, will lead to lower
