Market Equilibrium | 市场均衡考点精讲

📚 Market Equilibrium | 市场均衡考点精讲

Market equilibrium is central to IGCSE WJEC Economics. It explains how prices are determined by the interaction of buyers and sellers, and how markets adjust to restore balance when disturbed. This revision guide covers all the key concepts, diagrams, and exam techniques you need.

市场均衡是 IGCSE WJEC 经济学的核心内容。它解释了价格如何由买卖双方的互动决定，以及市场在受到干扰时如何调整以恢复平衡。本复习指南涵盖了你需要掌握的所有关键概念、图表和考试技巧。

1. Understanding Markets | 理解市场

A market is any arrangement that allows buyers and sellers to exchange goods, services, or resources. It can be a physical place like a farmers’ market, or a virtual platform like an e‑commerce website. In a free market, prices are the main signal guiding decisions.

市场是允许买卖双方交换商品、服务或资源的任何安排。它可以是一个像农贸市场那样的实体场所，或者像电子商务网站那样的虚拟平台。在自由市场中，价格是引导决策的主要信号。

The price mechanism operates without central direction, coordinating the plans of millions of consumers and producers. When economists refer to ‘the market’, they are usually talking about the forces of demand and supply that determine equilibrium.

价格机制在没有中央指令的情况下运行，协调着数以百万计的消费者和生产者的计划。当经济学家提到“市场”时，他们通常指的是决定均衡的供需力量。

2. Demand and Supply – A Quick Recap | 需求与供给 – 快速回顾

Demand is the quantity of a good or service that consumers are willing and able to purchase at various prices over a period, ceteris paribus. The demand curve slopes downward, illustrating the law of demand: as price falls, quantity demanded expands.

需求是指在其他条件不变的情况下，消费者在一段时期内愿意并且能够在不同价格水平上购买的商品或服务数量。需求曲线向下倾斜，说明了需求定律：价格下降时，需求量增加。

Supply is the quantity that producers are willing and able to offer for sale at different prices over a period, ceteris paribus. The supply curve slopes upward because higher prices provide an incentive to increase output and cover rising marginal costs.

供给是指在其他条件不变的情况下，生产者在一段时期内愿意并能够在不同价格水平上出售的数量。供给曲线向上倾斜，因为更高的价格提供了增加产出和覆盖不断上升的边际成本的激励。

It is vital to distinguish between a movement along a curve (caused by a change in the good’s own price) and a shift of the curve (caused by changes in non‑price determinants such as income, technology, or taxes).

区分沿曲线的移动（由商品自身价格变化引起）和曲线的平移（由收入、技术或税收等非价格决定因素的变化引起）至关重要。

3. Market Equilibrium – The Balancing Point | 市场均衡 – 平衡点

Market equilibrium occurs at the price where the quantity demanded exactly equals the quantity supplied. At this intersection of the demand and supply curves, there is no inherent tendency for the price to change – the market clears.

市场均衡发生在需求量恰好等于供给量的价格水平上。在需求曲线和供给曲线的这个交点上，价格没有内在的变化趋势——市场出清了。

The equilibrium price (Pₑ) is often called the market‑clearing price. At this price, buyers can purchase all they want and sellers can sell all they produce, so there is neither a shortage nor a surplus. The equilibrium quantity (Qₑ) is the amount traded.

均衡价格（Pₑ）通常被称为市场出清价格。在此价格下，买方可以买到他们想要的一切，卖方可以售出他们生产的一切，因此既没有短缺也没有过剩。均衡数量（Qₑ）是交易的数量。

Equilibrium condition: Qd = Qs

均衡条件：需求量 = 供给量

For example, if the demand function is Qd = 80 – 2P and supply is Qs = –10 + 4P, setting them equal gives 80 – 2P = –10 + 4P → 90 = 6P → Pₑ = 15. Substituting back, Qₑ = 80 – 2(15) = 50 units.

例如，如果需求函数为 Qd = 80 – 2P，供给函数为 Qs = –10 + 4P，令两者相等：80 – 2P = –10 + 4P → 90 = 6P → Pₑ = 15。代回得到 Qₑ = 80 – 2(15) = 50 单位。

4. Disequilibrium – Excess Demand (Shortage) | 不均衡 – 过度需求（短缺）

When the market price is set below equilibrium (P < Pₑ), the quantity demanded exceeds the quantity supplied (Qd > Qs). This situation is called excess demand, or a shortage. Consumers are willing to buy more than producers are willing to sell at that price.

当市场价格设定在均衡水平之下（P < Pₑ）时，需求量超过供给量（Qd > Qs）。这种情况被称为过度需求或短缺。消费者愿意购买的数量超过了生产者在该价格下愿意出售的数量。

The shortage puts upward pressure on price. Buyers compete for limited goods, bidding higher prices. As price rises, quantity demanded contracts (movement along the demand curve) and quantity supplied expands (movement along the supply curve) until the shortage is eliminated and equilibrium is restored.

短缺对价格产生上行压力。买方争抢有限商品，出价更高。随着价格上升，需求量收缩（沿需求曲线移动），供给量扩张（沿供给曲线移动），直到短缺消除，均衡恢复。

Numerical example: using the previous functions, if price is forced at 10, Qd = 80 – 20 = 60, Qs = –10 + 40 = 30. Shortage = 60 – 30 = 30 units. This shortage drives the price back towards 15.

数值例子：使用前面的函数，若价格被强行定在 10，则 Qd = 80 – 20 = 60，Qs = –10 + 40 = 30。短缺 = 60 – 30 = 30 单位。这种短缺推动价格回升至 15。

5. Disequilibrium – Excess Supply (Surplus) | 不均衡 – 过度供给（过剩）

If the price is above equilibrium (P > Pₑ), quantity supplied exceeds quantity demanded (Qs > Qd). This results in a surplus, or excess supply. Sellers find they cannot sell all their output, so unsold stocks accumulate.

如果价格高于均衡水平（P > Pₑ），供给量超过需求量（Qs > Qd）。这导致过剩，或过度供给。卖方发现无法出售所有产品，未售库存积压。

A surplus creates downward pressure on price. Firms reduce prices to clear excess stock. The falling price stimulates an expansion of demand and a contraction of supply. The surplus shrinks, and the market moves back toward equilibrium.

过剩对价格产生下行压力。企业降低价格以清理多余库存。价格下跌刺激需求扩张和供给收缩。过剩缩小，市场向均衡回归。

Using the same example, if price is 20, Qd = 80 – 40 = 40, Qs = –10 + 80 = 70. Surplus = 70 – 40 = 30 units. This forces the price down to 15.

使用同样的例子，如果价格为 20，Qd = 80 – 40 = 40，Qs = –10 + 80 = 70。过剩 = 70 – 40 = 30 单位。这迫使价格下降至 15。

6. The Price Mechanism – Signalling, Incentives and Rationing | 价格机制 – 信号、激励与配给

The price mechanism describes how the interacting forces of demand and supply determine market prices, and how those prices coordinate economic activity. It has three essential functions in a market economy.

价格机制描述了供需的相互作用如何决定市场价格，以及这些价格如何协调经济活动。在市场经济中，它具有三个基本功能。

Signalling: Prices convey information. A rising price signals that a good has become scarcer or more desired, encouraging producers to reallocate resources toward its production. A falling price signals the opposite.

信号：价格传递信息。价格上涨表明一种商品变得更稀缺或更受青睐，鼓励生产者将资源转向它的生产。价格下跌则发出相反的信号。

Incentivising: Price changes alter the rewards for consumers and producers. Higher prices incentivise firms to increase output (profit motive) and discourage consumption. Lower prices encourage consumption and may drive some producers out of the market.

激励：价格变化改变了消费者和生产者的回报。更高价格激励企业增加产出（利润动机）并抑制消费。更低价格鼓励消费并可能将一些生产者逐出市场。

Rationing: When a resource is scarce, a higher price rations it to those most willing and able to pay, preventing over‑use and ensuring that the limited supply is allocated to those who value it most.

配给：当资源稀缺时，较高的价格将其配给最愿意且能够支付的人，防止过度使用，并确保有限的供给分配给最重视它的人。

Together these functions guide the allocation of scarce resources without the need for a central planner. The equilibrium price ensures that consumer sovereignty and producer efficiency are aligned.

这些功能共同引导稀缺资源的配置，无需中央计划者。均衡价格确保了消费者主权和生产者效率得以协调。

7. How a Change in Demand Affects Equilibrium | 需求变化如何影响均衡

A change in any non‑price determinant of demand (such as income, tastes, prices of substitutes or complements, population) will shift the entire demand curve. An increase in demand shifts the curve to the right; a decrease shifts it to the left.

需求的任何非价格决定因素（如收入、偏好、替代品或互补品价格、人口）的变化，都会使整个需求曲线移动。需求增加使曲线右移；需求减少使曲线左移。

When demand increases, at the original equilibrium price there is now a shortage (Qd > Qs). This exerts upward pressure on price. As price rises, quantity supplied expands along the existing supply curve, and a new equilibrium is established at a higher price and higher quantity: P ↑, Q ↑.

当需求增加时，在原来的均衡价格下会出现短缺（Qd > Qs）。这对价格产生上行压力。随着价格上升，供给量沿

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Market Equilibrium | 市场均衡考点精讲