📚 Year 12 Cambridge Economics: Core Knowledge Review | 剑桥AS经济核心知识点梳理
This article provides a structured recap of the essential concepts in the Cambridge AS Economics syllabus. It covers fundamental ideas from the basic economic problem to government intervention, helping Year 12 students consolidate their understanding in both English and Chinese.
本文系统梳理了剑桥AS经济学的核心概念，从基本经济问题到政府干预，帮助Year 12学生巩固理解，并提供中英双语对照，方便复习。
1. The Basic Economic Problem and Factors of Production | 基本经济问题与生产要素
The fundamental economic problem arises because resources are scarce while human wants are unlimited. This forces individuals, firms and governments to make choices, and every choice involves an opportunity cost — the next best alternative forgone.
基本经济问题源于资源稀缺与人类无限欲望之间的矛盾。个人、企业和政府都必须做出选择，而每一次选择都意味着机会成本，即所放弃的次优替代方案。
Land, labour, capital and enterprise are the four factors of production. Land includes all natural resources; labour is the human effort; capital refers to man‑made goods used in production; and enterprise is the willingness to take risks and organise the other three factors.
土地、劳动、资本和企业家才能是四种生产要素。土地涵盖所有自然资源；劳动指人的努力；资本是用于生产的人造物品；企业家才能则指承担风险并组织其他生产要素的能力。
2. Opportunity Cost and Production Possibility Curve | 机会成本与生产可能性曲线
Opportunity cost is the value of the next best alternative sacrificed when an economic decision is made. It is central to evaluating trade‑offs in resource allocation.
机会成本是做出经济决策时所放弃的次优选项的价值，是评估资源配置权衡的核心概念。
A production possibility curve (PPC) shows the maximum combinations of two goods an economy can produce with full employment of its resources. Points on the curve represent productive efficiency, while points inside indicate unemployed resources. An outward shift of the PPC signals economic growth.
生产可能性曲线（PPC）展示了一个经济体在充分利用资源时所能生产的两种商品的最大组合。曲线上的点代表生产效率，曲线内的点表示资源未充分利用。PPC向外移动则意味着经济增长。
3. Demand | 需求
Demand represents the willingness and ability of consumers to purchase a good at various prices over a given period. The law of demand states that, ceteris paribus, as price falls, quantity demanded rises, and vice versa.
需求是指消费者在不同价格水平下愿意并能够购买某种商品的数量。需求定律指出，在其他条件不变的情况下，价格下降时需求量上升，价格上升时需求量下降。
A movement along the demand curve is caused only by a change in the good's own price. A shift of the demand curve, however, results from changes in non‑price determinants such as income, tastes, prices of related goods, expectations, and the number of buyers.
仅由商品自身价格变化引起的是沿需求曲线的移动。需求曲线的平移则是由非价格决定因素的变化引起的，例如收入、偏好、相关商品价格、预期以及买家数量。
4. Supply | 供给
Supply is the quantity of a good producers are willing and able to offer for sale at different prices. The law of supply indicates a positive relationship between price and quantity supplied, ceteris paribus.
供给是指生产者在不同价格下愿意并能够提供的商品数量。供给定律表明，在其他条件不变时，价格与供给量呈正相关关系。
A change in the good's own price causes a movement along the supply curve. Shifts of the supply curve occur when non‑price factors alter, such as costs of production, technology, taxes, subsidies, expectations, and the number of suppliers.
商品自身价格变化引起供给曲线上的移动。生产成本、技术、税收、补贴、预期和供应商数量等非价格因素变化时，则会导致供给曲线的平移。
5. Market Equilibrium and the Price Mechanism | 市场均衡与价格机制
Market equilibrium occurs where quantity demanded equals quantity supplied. At this point there is no tendency for price to change, and the market clears.
市场均衡发生在需求量等于供给量时。此时价格没有变动的趋势，市场出清。
The price mechanism describes how changes in demand and supply determine the allocation of resources. Prices act as signals to producers and consumers, ration scarce resources, and provide incentives — these are the signalling, rationing, and incentive functions.
价格机制描述了需求与供给变化如何决定资源配置。价格向生产者和消费者传递信号，配给稀缺资源，并提供激励——这就是信号功能、配给功能和激励功能。
6. Price Elasticity of Demand (PED) | 需求的价格弹性
PED measures the responsiveness of quantity demanded to a change in price. It is calculated as the percentage change in quantity demanded divided by the percentage change in price.
PED = %ΔQd / %ΔP
PED衡量需求量对价格变化的反应程度。计算公式为需求量变动百分比除以价格变动百分比。
Demand is price elastic when |PED| > 1, price inelastic when |PED| < 1, unit elastic when |PED| D influences total revenue: if demand is elastic, a price fall raises total revenue; if inelastic, a price fall lowers total revenue.
当|PED| > 1时需求富有弹性，|PED| < 1时缺乏弹性，|PED| = 1时为单位弹性，PED = ∞为完全弹性，PED = 0为完全无弹性。PED影响总收益：弹性需求下降价增加总收益，缺乏弹性时降价减少总收益。
7. Price Elasticity of Supply (PES) | 供给的价格弹性
PES measures the responsiveness of quantity supplied to a change in price. It is calculated as the percentage change in quantity supplied divided by the percentage change in price.
PES = %ΔQs / %ΔP
PES衡量供给量对价格变化的反应程度。计算公式为供给量变动百分比除以价格变动百分比。
e period, availability of stocks, spare capacity, and the ease of switching production. Supply tends to be more price elastic in the long run.
PES > 1时供给富有弹性，PES < 1时缺乏弹性，PES = 1时为单位弹性。关键决定因素包括时间周期、库存可得性、闲置产能以及转换生产的难易程度。长期中供给通常更具价格弹性。
8. Other Elasticities (YED, XED) | 其他弹性（收入弹性、交叉弹性）
city of demand (YED) measures how responsive quantity demanded is to a change in consumers' income. YED = %ΔQd / % ry goods have YED > 1; necessity goods have 0 < YED < 1; inferior goods have negative YED.
需求的收入弹性（YED）衡量需求量对消费者收入变化的反应程度。YED = %ΔQd / %ΔY。正常品YED为正，奢侈品YED > 1，必需品0 < YED < 1，低档品YED为负。
Cross‑ the responsiveness of demand for one good to a change in the price of another good. XED = %ΔQd of good A / %ΔP of good B. Substitutes have positive XED; complements have negative XED.
需求的交叉弹性（XED）衡量一种商品的需求对另一种商品价格变化的反应程度。XED = 商品A需求量变动百分比 / 商品B价格变动百分比。替代品XED为正，互补品XED为负。
9. Consumer and Producer Surplus | 消费者与生产者剩余
Consumer surplus is the difference between the maximum price consumers are willing to pay and the market price they actually pay. It represents the extra welfare consumers gain from market transactions.
消费者剩余是消费者愿意支付的最高价格与实际支付的市场价格之间的差额，代表消费者在市场交易中获得的额外福利。
Producer surplus is the difference between the market price producers receive and the minimum price they are willing to accept. Together, consumer and producer surplus form community surplus, a measure of overall market welfare.
生产者剩余是生产者获得的市场价格与其愿意接受的最低价格之间的差额。消费者剩余与生产者剩余之和构成社会总剩余，是衡量整体市场福利的指标。
10. Market Failure and Externalities | 市场失灵与外部性
Market failure occurs when the free market fails to allocate resources efficiently, leading to a loss of community surplus. One major cause is externalities — costs or benefits imposed on third parties not directly involved in the transaction.
当自由市场无法有效配置资源，导致社会总剩余损失时，就出现市场失灵。一个主要原因是外部性——强加给未直接参与交易的第三方的成本或收益。
Negative externalities, such as pollution, cause overproduction and overconsumption because the free market underestimates the true social cost. Positive externalities, such as education, cause underproduction and underconsumption because private benefits fall short of social benefits. In both cases, the market equilibrium deviates from the socially optimal level.
负外部性（如污染）导致生产过度和消费过度，因为自由市场低估了真实的社会成本。正外部性（如教育）导致生产不足和消费不足，因为私人收益低于社会收益。这两种情况都使市场均衡偏离社会最优水平。
11. Government Intervention: Indirect Taxes and Subsidies | 政府干预：间接税与补贴
Governments impose indirect taxes on goods with negative externalities to internalise the externality. A tax raises the cost of production, shifts the supply curve to the left, increases price, and reduces quantity, moving the market closer to the social optimum.
政府对具有负外部性的商品征收间接税，以使外部性内部化。税收提高生产成本，使供给曲线左移，推高价格，减少数量，从而使市场更接近社会最优。
Subsidies are payments from the government to producers of goods with positive externalities. A subsidy lowers production costs, shifts the supply curve to the right, lowers price, and increases quantity, encouraging socially desirable consumption and production.
补贴是政府向具有正外部性的商品生产者提供的支付。补贴降低生产成本，使供给曲线右移，降低价格，增加数量，鼓励对社会有益的消费和生产。
12. Government Intervention: Maximum and Minimum Prices | 政府干预：最高限价与最低限价
A maximum price (price ceiling) is set below the equilibrium price to make necessities, such as rent, more affordable. However, it can create persistent shortages and encourage the emergence of black markets if left unmanaged.
最高限价（价格天花板）被设定在均衡价格以下，使必需品（如房租）更便宜。但如果管理不当，可能会导致持续短缺，并催生黑市。
A minimum price (price floor) is set above the equilibrium price to protect producers' income, for example in agriculture. This leads to excess supply, which the government may need to purchase and store, resulting in opportunity costs and possible inefficiency.
最低限价（价格地板）被设定在均衡价格以上，以保护生产者收入，例如在农业领域。这会导致供给过剩，政府可能需要购买并储存剩余产品，从而产生机会成本和可能的无效率。
Published by TutorHao | Economics Revision Series | aleveler.com
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