Production, Cost & Perfect Competition
AP Microeconomics Topic 3 8:56 English narration · English + 中文 subtitles burned in
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Transcript
Picture a small bakery with one kitchen and one oven.
设想一家小面包店，只有一个厨房、一个烤箱。
Hire your first baker and you get thirty extra loaves a day.
雇第一个面包师， 你每天多得三十个面包。
Hire a second and you get twenty-six more.
雇第二个，多得二十六个。
A third adds twenty.
第三个再多二十个。
By the fifth, the kitchen is crowded and you gain almost nothing.
到了第五个，厨房挤得转不开身，几乎什么也增加不了。
The oven never grew.
烤箱始终没有变大。
That is the law of diminishing marginal returns, and it quietly shapes every cost curve in this unit.
这就是边际收益递减法则，它悄悄决定了本单元里每一条成本曲线的形状。
Today we go inside the firm.
今天我们走进企业内部。
How inputs become output.
投入如何变成产出。
How that shapes the cost curves.
这如何决定成本曲线的形状。
The difference between accounting profit and economic profit.
会计利润与经济利润的区别。
The one rule that maximises profit.
使利润最大化的那一条规则。
And the market economists use as their benchmark.
以及经济学家用作基准的那种市场。
Let's begin.
让我们开始吧。
The production function links inputs to output.
生产函数把投入和产出联系起来。
In the short run at least one input, usually the factory or the machines, is fixed.
在短期，至少有一种投入是固定的， 通常是厂房或机器。
Total product is everything the firm makes.
总产量是企业生产的全部。
Marginal product is the extra output from one more worker.
边际产量是多雇一个工人所带来的额外产出。
Average product is output per worker.
平均产量是人均产出。
Now watch the marginal product curve.
现在看边际产量曲线。
It rises at first, because workers can specialise, then it falls once the fixed equipment is crowded.
它一开始上升，因为工人可以分工； 随后，当固定设备被挤满时，它就下降。
And this drives the costs: when marginal product rises, marginal cost falls, and when marginal product falls, marginal cost rises.
而这决定了成本： 边际产量上升时，边际成本下降；边际产量下降时，边际成本上升。
Here are the curves that come out of it.
由此得到的就是这些曲线。
Costs split into fixed and variable.
成本分为固定成本和可变成本。
Fixed cost does not change with output — the rent on the factory.
固定成本不随产量变化——比如厂房的租金。
Variable cost rises with output — materials, labour and the capital the firm can still vary.
可变成本随产量上升——比如原材料和人工。
Together they are total cost.
两者加起来就是总成本。
But the exam works in per-unit terms, so watch marginal cost, average variable cost and average total cost appear.
但考试要看的是单位成本，所以请看边际成本、平均可变成本 和平均总成本依次出现。
Let's read them carefully.
我们仔细读一读。
Total cost splits in two: fixed cost, which you pay whatever you make, and variable cost, which grows with output.
总成本分成两部分：固定成本，不论你生产多少都要付； 以及可变成本，它随产量增长。
Now the shapes.
现在看形状。
Average fixed cost falls the whole way, because one rent bill is spread over more and more units.
平均固定成本一路下降，因为一笔租金被分摊到越来越多的产品上。
Average variable cost and average total cost are both U-shaped.
平均可变成本和平均总成本都是U形的。
Marginal cost is the cost of making one more unit, and it is U-shaped too.
边际成本是多生产一单位的成本，它也是U形的。
Two facts the exam always wants. Marginal cost is the mirror image of marginal product: when M P rises, M C falls, and the other way round. And M C cuts both A V C and A T C at their minimum points — when marginal is below average the average falls, when it is above the average rises.
而这就是考试永远要考的规则：边际成本正好在两条平均曲线的最低点穿过它们。
In the long run nothing is fixed.
在长期，没有什么是固定的。
The firm can change its factory, its machines, everything.
企业可以改变厂房、机器，改变一切。
So only one curve is left: long-run average total cost, L R A T C.
所以只剩下一条曲线：长期平均总成本。
When it falls as the firm grows, that is economies of scale — bulk buying, specialised staff, better machines.
当它随企业变大而下降时，那就是规模经济——批量采购、专业化的员工、更好的机器。
When it rises, that is diseconomies of scale: the firm has grown too big to manage well.
当它上升时，那就是规模不经济：企业大到难以有效管理。
Flat in between is constant returns to scale.
而且不要把它和边际收益递减混为一谈。
And do not mix these up with diminishing returns. Diminishing returns is a short-run idea, with one input fixed. Economies of scale is long run, with everything free to change.
边际收益递减是短期概念，有一种投入是固定的； 规模经济是长期概念，一切都可以改变。
Now profit — there are three types of it, and economists count them differently.
现在说利润——经济学家的算法不一样。
A shopkeeper takes in two hundred thousand dollars and pays one hundred and twenty thousand in explicit costs, the money that actually leaves her hand.
一位店主收入二十万美元，付出十二万美元的显性成本，也就是真正花出去的钱。
Accounting profit is what is left: eighty thousand.
会计利润就是剩下的：八万美元。
But she also gave up a seventy thousand dollar salary, and five thousand of interest.
但她还放弃了一份七万美元的薪水，以及五千美元的利息。
Those are implicit costs — the opportunity cost of her own resources.
这些是隐性成本——她自己资源的机会成本。
Economic profit subtracts those too, so it is only five thousand.
经济利润把这些也减掉，所以只有五千美元。
And zero economic profit is not failure: it means she earns exactly her next best alternative.
而经济利润为零并不是失败：它意味着她挣到的正好等于次优选择的价值。
We call that normal profit.
我们把它叫做正常利润。
Every firm, in every market, does its profit maximization with one rule: marginal revenue equals marginal cost.
每一家企业、在每一种市场结构中，都用同一条规则实现利润最大化： 边际收益等于边际成本。
Think about why.
想想为什么。
While marginal revenue is above marginal cost, that extra unit earns more than it costs, so make it.
当边际收益高于边际成本时，那一单位赚的比花的多，所以要生产。
Once marginal cost climbs above marginal revenue, the extra unit costs more than it earns, so do not make it.
一旦边际成本超过边际收益，那一单位花的比赚的多，就不要生产。
So you stop exactly where the two are equal.
所以你正好停在两者相等之处。
Produce less and you leave money on the table; produce more and you lose money on every extra unit.
生产得少了，你就白白放过了利润； 生产得多了，每多一单位都在亏钱。
But finding that quantity is not the whole decision.
但找到那个产量还不是全部决策。
The firm is also deciding whether to produce at all, and later whether to enter or exit.
企业还要问：到底要不要开工。
Look at three prices.
看这三个价格。
If the price is above average total cost, the firm makes an economic profit.
如果价格高于平均总成本，企业获得经济利润。
If the price sits between average variable cost and average total cost, the firm is losing money, but the price still covers the variable cost, so it keeps producing and loses less than its rent.
如果价格位于平均可变成本和平均总成本之间，企业在亏钱， 但价格仍然能覆盖可变成本，所以它继续生产，亏得比租金还少。
If the price falls below average variable cost, it should shut down and lose only the fixed cost.
如果价格跌破平均可变成本，它就应该停业，只亏掉固定成本。
That is the shutdown rule in the short run: keep producing only while price covers A V C. And it is why the firm's short-run supply curve is its M C curve above minimum A V C.
这也正是为什么企业的供给曲线，就是平均可变成本最低点以上的那段边际成本曲线。
Now the benchmark market: perfect competition.
现在来看作为基准的市场：完全竞争。
A perfectly competitive market needs four things.
它需要四个条件。 许多小企业。
Many small firms. An identical product, so one seller's is the same as another's.
产品完全相同，一个卖者的和另一个的没有区别。
Free entry and exit.
自由进入和退出。
And perfect information.
以及完全信息。
Put those together and every firm is a price taker: far too small to move the price on its own.
把这些放在一起，每家企业都是价格接受者：小到根本无法自己撼动价格。
So the firm does not face a downward sloping demand curve at all. It faces a horizontal line at the market price, which means price, marginal revenue and average revenue are all the same number.
所以企业面对的根本不是一条向下倾斜的需求曲线， 而是市场价格处的一条水平线——这意味着价格、边际收益和平均收益是同一个数。
This is the diagram examiners ask for, and it has two panels.
这就是考官要的那张图，它有两个面板。
On the left is the market: supply and demand cross and fix the price.
左边是市场：供给和需求相交，定下价格。
On the right is one single firm, drawn at a completely different scale.
右边是单独一家企业，画在完全不同的尺度上。
The firm cannot change that price, so it takes it as a horizontal line.
企业无法改变那个价格，所以它把价格当作一条水平线接受下来。
It then produces where marginal cost meets that line.
然后它在边际成本与这条线相交的地方生产。
Here the price sits above average total cost, so the shaded box is economic profit.
这里价格高于平均总成本，所以那块阴影就是经济利润。
And that profit is exactly what will not last.
而这份利润，恰恰是维持不下去的。
Because entry is free, that profit attracts new firms.
因为可以自由进入，那份利润会吸引新企业。
They join, market supply shifts right, and the price falls.
它们加入市场，市场供给向右移动，价格下降。
It keeps falling until there is no economic profit left, and that happens exactly when the price touches the lowest point of average total cost.
价格一直下降，直到再也没有经济利润为止； 而这恰好发生在价格触到平均总成本最低点的时候。
Losses work the same way in reverse: firms exit until the price rises back.
亏损则以相反的方式起作用：企业退出，直到价格回升。
So in long-run equilibrium the firm sits at minimum A T C, earning normal profit, and it is efficient twice over.
所以在长期，企业停在那个最低点，只赚正常利润，而且在两个意义上都是有效率的。
It is allocatively efficient — allocative efficiency — because price equals marginal cost, so exactly the right amount is made; and productively efficient — productive efficiency — because entry has driven price down to minimum average total cost, so goods are made as cheaply as possible.
价格等于边际成本，所以产量恰好是该生产的数量——这是配置效率； 进入把价格压到了平均总成本的最低点，所以东西是以尽可能低的成本生产的—— 这是生产效率。
The price itself is the signal that carries all of that information.
而价格本身，就是承载所有这些信息的信号。
Let's put numbers on it.
我们代入数字。
A firm's fixed cost is one hundred dollars.
一家企业的固定成本是一百美元。
At ten units, total cost is three hundred; at eleven units it is three hundred and twenty-five.
在十单位时，总成本是三百美元；在十一单位时是三百二十五美元。
Find the three average costs at ten units, and the marginal cost of the eleventh.
求十单位时的三种平均成本，以及第十一单位的边际成本。
Pause here and try it.
先暂停，自己试一试。
Ready?
好了吗？
Variable cost is three hundred minus one hundred, so two hundred; divide by ten and average variable cost is twenty.
可变成本是三百减一百，等于二百； 除以十，平均可变成本是二十。
Average total cost is three hundred over ten, which is thirty; average fixed cost is ten.
平均总成本是三百除以十，等于三十； 平均固定成本是十。
And marginal cost is the change in total cost, twenty-five dollars.
而边际成本是总成本的变化量，二十五美元。
Notice the check: ten plus twenty is thirty.
注意验算：十加二十等于三十。
Three marks students give away.
三个学生白白丢掉的分。
First, marginal cost always cuts average variable and average total cost at their lowest points — draw it that way every time.
第一，边际成本永远在平均可变成本和平均总成本的 最低点穿过它们——每次都要这样画。
Second, keep the runs apart: diminishing returns is short run, economies of scale is long run.
第二，把两个"期"分清楚：边际收益递减是短期，规模经济是长期。
Third, economic profit subtracts the implicit costs as well, so it is always smaller than accounting profit.
第三，经济利润还要减去隐性成本，所以它总是小于会计利润。
Get those right, and this unit is yours.
把这些做对，这个单元就是你的了。