理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

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来自 University of Pennsylvania 的课程

微观经济学：当市场“失灵”时

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理想状态下的市场能够达到高效生产：将总剩余(total surplus)最大化。 但是在现实中的市场并非完美。在本课程中，我们将探索一系列市场存在着缺陷的情形并且理解为什么会出现这些缺陷；同时，我们会了解一些改进措施，比如反托拉斯(antitrust)政策以及其他一些政府的干预措施。 我们会选取日常中的例子——从我们每天购买和享用的货物和服务开始。我们也会在每周的练习里把理论运用到时下大事和政策研讨中。 所有的这些都会使你成为一个可以理解、分析和评价市场结果的，有学识的，有批判精神的思考者。

从本节课中

Monopoly

A monopoly is a case where there is only one firm in the market. We will define and model this case and explain why market power is good for the firm, bad for consumers. We will also show that society as a whole suffers from the lack of competition.

- Rebecca SteinSenior Lecturer

Economics

[MUSIC]

Let's think through a graphical interpretation of this marginal revenue.

We know what revenue is, it's price times quantity so if the price is $100 and

we're selling 50 units, the revenue is this rectangle here.

If the monopoly wants to sell an additional unit,

we said they had to lower the price to $99.

And what's important to realize is that they're lowering the price not just to

the last unit, but to all the units.

So they're lowering the price to everyone down to $99.

So the new revenue is this new price, 99, times this new quantity, 51.

So if we want to compare these two rectangles,

what is the difference between them?

On the one hand by selling an additional unit, the monopolist gains something.

They gain this rectangle here.

This is the addition from selling the extra unit.

But on the other hand they also lose something.

What do they lose?

They lose the fact that they had to lower the price on each of the existing units.

So what is our marginal revenue?

Our marginal revenue is the difference between what they gained

and the fact that they had to give a discount on all the previous units.

Let's calculate these areas.

What they gained is the fact that they're selling 1 unit at the going price of $99.

So this rectangle is equal to $99.

On the other hand, there's the discount on all the previous units.

A discount of $1 times all the previous units which is 50,

and once again, we get that the marginal revenue is equal to $49.

And clearly it has to be less than the price because this rectangle,

this is the price of $99.

And the marginal revenue is this price minus this rectangle.

So again, marginal revenue is less than the price.