完全竞争市场上的厂商均衡
7.2 The Equilibrium of the Firm under
Perfect Competition
教学目标 Objectives：
? 了解完全竞争的市场条件
? 掌握完全竞争市场的需求曲线和收益曲线
? 掌握完全竞争市场的短期均衡条件
? 掌握完全竞争市场的长期均衡条件
知识点 Knowledge：
完全竞争的市场条件, 完全竞争市场的需求曲线和收益曲线
完全竞争市场的短期均衡和长期均衡条件
技能点 Skills：
绘制完全竞争市场均衡图
price taker
advertising
market opportunities
ideal type
advantages
shortcomings
government
Normal profit
Supernormal profit least-cost
economic profit
abnormal profit homogeneous product
economies of scale industry
专业词汇 Professional terms
一、完全竞争的含义与条件
Assumptions
l Firms are price taker.
l There is complete freedom of entry into the industry for
new firms.
l All firms produce an identical product,The product is
homogeneous,so there is no branding and advertising.
l Producers and consumers have perfect knowledge of the
market,That is,producers are fully aware of prices,costs and
market opportunities,Consumers are fully aware of the price,
quantity and availability of the product.
Nevertheless,despite the lack of real-world cases,
the model of perfect competition plays a very
important role in economic analysis and policy,Its
major relevance is as an ‘ideal type’,Many on the
political right argue that perfect competition brings
a number of important advantages,The model can
thus be used as a standard against which to judge
the shortcomings of real world industries,It can
help government to formulate policies towards
industry.
一、完全竞争的含义与条件
实现完全竞争的条件包括：
?第一, 市场上有许多生产者与消费者, 每一个生产者的
销售量与消费者的购买量只占市场极小的份额 。
?第二, 市场上的产品是同质的, 即不存在产品差别 。
?第三, 资源完全自由流动 。
?第四, 市场信息是畅通的 。
一、完全竞争的含义与条件
The short run and the long run
l The short run under perfect competition The period
during which there is too little time for new firms to enter the
industry.
l The long run under perfect competition The period of
time that is long enough for new firms to enter the industry.
Normal profit The opportunity cost of being in business,the
profit that could have been earned in the next best alternative
business,It is counted as a cost of production.
Supernormal profit (also known as pure profit,economic
profit,abnormal profit or simply profit) The excess of total
profit above normal profit.
二、完全竞争市场上的需求和收益曲线
0 Q 0 Q 0 Q1 Q2 Q
TR
完全竞争市场上的需求曲线与收益曲线
P P
P0P0
D S
E
d
(MR=AR=P)
(a) (c)(b)
TR2
TR1
TR
Q
三、完全竞争市场上的短期均衡
完全竞争市场均衡图
0 QE Q
P
E
d（ MR=AR=P）P
E
SMC
三、完全竞争市场上的短期均衡
P
E
SMC
SAC
PE d（ MR=AR=P）
0 QE Q
完全竞争市场厂商盈亏平衡图
?厂商获得正常利润 (normal profit)
三、完全竞争市场上的短期均衡
?厂商获得超额利润 (supernormal profit)
F
d（ MR=AR=P）
E
SMC
SAC
P
PE
PF
0 QE Q
完全竞争厂商取得超额利润分析图
三、完全竞争市场上的短期均衡
?厂商遭受亏损
SMC
SAC
d（ MR=AR=P）
F
E
P
PF
PE
0 QE Q
完全竞争亏损厂商均衡分析图
三、完全竞争市场上的短期均衡
A
C
B
SMC
SAC
AVC
P
PA
PB
PC d(AR=MR=PB)
亏损企业经营规模调整分析图
四、完全竞争市场上的长期均衡
Revenue
and
cost
0 Quantity
P=AR=
MR
AC
M
C
P
Q
NORMAL
PROFIT
五、对完全竞争市场的评论
?In many industries,firms may have to be quite large if
they are to experience the full potential economies of
scale,But perfect competition requires there to be many
firms,Firms must therefore be small in most for
economies of scale.
?Once a firm expands sufficiently to achieve economies
of scale,it will usually gain market power,It will be able
to undercut the prices of smaller firms,which will thus
be driven out of business,Perfect competition is
destroyed.
?Perfect competition could only exist in any industry,
therefore,if there were no (or virtually no) economies of
scale.
Perfect competition and the public interest
There are a number of features of perfect competition
which,it could be argued,benefit society:
l Price equals marginal cost,which has important
implications for the allocation of resources between
alternative products.
?l If a firm becomes less efficient than other firms,it
will make less than normal profits and be driven out of
business,If it is more efficient,it will earn supernormal
profits,Thus the competition between firms will act as a
spur to efficiency.
?l Similarly,the desire for supernormal profit,and the
desire to avoid loss,will encourage the development of
new technology.
Perfect competition and the public interest
?l There is no point in advertising under perfect competition,
since all firms produce a homogeneous product.This and the
previous two factors will lead to low AC curves,and hence to an
economical use of the nation’s scarce resources.
?l For any given technology,the firm,in the long run,will
produce at the least-cost output.
?l The consumer gains from low prices,since not only are costs
kept low,but also there are no long-run supernormal profits to
these costs.
?l If consumer tastes change,the resulting price change,the
resulting price change will lead firms to respond (purely out of
self-interest),An increased consumer demand will call forth extra
supply with only a short-run increase in profit.
五、对完全竞争市场的评论
?第一, 社会供给与需求相等, 使资源得到最优配置,
生产者的生产不会有不足或过剩, 消费者的需求也得
到了充分满足 。
?第二, 在长期均衡时所达到的平均成本处于最低点,
表明可以通过完全竞争与资源的自由流动, 使生产要
素的效率得到最有效的发挥 。
?第三, 平均成本最低决定了产品的价格也是最低的,
这对消费者是有利的 。
益处：
五、对完全竞争市场的评论
?第一, 各厂商的平均成本最低并不一定是社会成本
最低 。
?第二, 产品无差别, 这样, 消费者的多种需求无法
得到满足 。
?第三, 完全竞争市场上生产者的规模都很小, 这样,
他们没有能力去实现重大的科学技术突破, 从而不利
于科学技术发展和科技创新 。
?第四, 在实际经济生活中, 完全竞争的情况是很少
的, 而且, 一般来说, 竞争也必然引起垄断 。
弊端：
7.2 The Equilibrium of the Firm under
Perfect Competition
教学目标 Objectives：
? 了解完全竞争的市场条件
? 掌握完全竞争市场的需求曲线和收益曲线
? 掌握完全竞争市场的短期均衡条件
? 掌握完全竞争市场的长期均衡条件
知识点 Knowledge：
完全竞争的市场条件, 完全竞争市场的需求曲线和收益曲线
完全竞争市场的短期均衡和长期均衡条件
技能点 Skills：
绘制完全竞争市场均衡图
price taker
advertising
market opportunities
ideal type
advantages
shortcomings
government
Normal profit
Supernormal profit least-cost
economic profit
abnormal profit homogeneous product
economies of scale industry
专业词汇 Professional terms
一、完全竞争的含义与条件
Assumptions
l Firms are price taker.
l There is complete freedom of entry into the industry for
new firms.
l All firms produce an identical product,The product is
homogeneous,so there is no branding and advertising.
l Producers and consumers have perfect knowledge of the
market,That is,producers are fully aware of prices,costs and
market opportunities,Consumers are fully aware of the price,
quantity and availability of the product.
Nevertheless,despite the lack of real-world cases,
the model of perfect competition plays a very
important role in economic analysis and policy,Its
major relevance is as an ‘ideal type’,Many on the
political right argue that perfect competition brings
a number of important advantages,The model can
thus be used as a standard against which to judge
the shortcomings of real world industries,It can
help government to formulate policies towards
industry.
一、完全竞争的含义与条件
实现完全竞争的条件包括：
?第一, 市场上有许多生产者与消费者, 每一个生产者的
销售量与消费者的购买量只占市场极小的份额 。
?第二, 市场上的产品是同质的, 即不存在产品差别 。
?第三, 资源完全自由流动 。
?第四, 市场信息是畅通的 。
一、完全竞争的含义与条件
The short run and the long run
l The short run under perfect competition The period
during which there is too little time for new firms to enter the
industry.
l The long run under perfect competition The period of
time that is long enough for new firms to enter the industry.
Normal profit The opportunity cost of being in business,the
profit that could have been earned in the next best alternative
business,It is counted as a cost of production.
Supernormal profit (also known as pure profit,economic
profit,abnormal profit or simply profit) The excess of total
profit above normal profit.
二、完全竞争市场上的需求和收益曲线
0 Q 0 Q 0 Q1 Q2 Q
TR
完全竞争市场上的需求曲线与收益曲线
P P
P0P0
D S
E
d
(MR=AR=P)
(a) (c)(b)
TR2
TR1
TR
Q
三、完全竞争市场上的短期均衡
完全竞争市场均衡图
0 QE Q
P
E
d（ MR=AR=P）P
E
SMC
三、完全竞争市场上的短期均衡
P
E
SMC
SAC
PE d（ MR=AR=P）
0 QE Q
完全竞争市场厂商盈亏平衡图
?厂商获得正常利润 (normal profit)
三、完全竞争市场上的短期均衡
?厂商获得超额利润 (supernormal profit)
F
d（ MR=AR=P）
E
SMC
SAC
P
PE
PF
0 QE Q
完全竞争厂商取得超额利润分析图
三、完全竞争市场上的短期均衡
?厂商遭受亏损
SMC
SAC
d（ MR=AR=P）
F
E
P
PF
PE
0 QE Q
完全竞争亏损厂商均衡分析图
三、完全竞争市场上的短期均衡
A
C
B
SMC
SAC
AVC
P
PA
PB
PC d(AR=MR=PB)
亏损企业经营规模调整分析图
四、完全竞争市场上的长期均衡
Revenue
and
cost
0 Quantity
P=AR=
MR
AC
M
C
P
Q
NORMAL
PROFIT
五、对完全竞争市场的评论
?In many industries,firms may have to be quite large if
they are to experience the full potential economies of
scale,But perfect competition requires there to be many
firms,Firms must therefore be small in most for
economies of scale.
?Once a firm expands sufficiently to achieve economies
of scale,it will usually gain market power,It will be able
to undercut the prices of smaller firms,which will thus
be driven out of business,Perfect competition is
destroyed.
?Perfect competition could only exist in any industry,
therefore,if there were no (or virtually no) economies of
scale.
Perfect competition and the public interest
There are a number of features of perfect competition
which,it could be argued,benefit society:
l Price equals marginal cost,which has important
implications for the allocation of resources between
alternative products.
?l If a firm becomes less efficient than other firms,it
will make less than normal profits and be driven out of
business,If it is more efficient,it will earn supernormal
profits,Thus the competition between firms will act as a
spur to efficiency.
?l Similarly,the desire for supernormal profit,and the
desire to avoid loss,will encourage the development of
new technology.
Perfect competition and the public interest
?l There is no point in advertising under perfect competition,
since all firms produce a homogeneous product.This and the
previous two factors will lead to low AC curves,and hence to an
economical use of the nation’s scarce resources.
?l For any given technology,the firm,in the long run,will
produce at the least-cost output.
?l The consumer gains from low prices,since not only are costs
kept low,but also there are no long-run supernormal profits to
these costs.
?l If consumer tastes change,the resulting price change,the
resulting price change will lead firms to respond (purely out of
self-interest),An increased consumer demand will call forth extra
supply with only a short-run increase in profit.
五、对完全竞争市场的评论
?第一, 社会供给与需求相等, 使资源得到最优配置,
生产者的生产不会有不足或过剩, 消费者的需求也得
到了充分满足 。
?第二, 在长期均衡时所达到的平均成本处于最低点,
表明可以通过完全竞争与资源的自由流动, 使生产要
素的效率得到最有效的发挥 。
?第三, 平均成本最低决定了产品的价格也是最低的,
这对消费者是有利的 。
益处：
五、对完全竞争市场的评论
?第一, 各厂商的平均成本最低并不一定是社会成本
最低 。
?第二, 产品无差别, 这样, 消费者的多种需求无法
得到满足 。
?第三, 完全竞争市场上生产者的规模都很小, 这样,
他们没有能力去实现重大的科学技术突破, 从而不利
于科学技术发展和科技创新 。
?第四, 在实际经济生活中, 完全竞争的情况是很少
的, 而且, 一般来说, 竞争也必然引起垄断 。
弊端：
