Demand and Supply in CCEA IGCSE Economics | IGCSE CCEA 经济：需求与供给考点精讲

📚 Demand and Supply in CCEA IGCSE Economics | IGCSE CCEA 经济：需求与供给考点精讲

Demand and supply form the core of market economies. In CCEA IGCSE Economics, a solid grasp of how buyers and sellers interact is essential for explaining price determination, market outcomes, and government policy effects. This revision guide walks you through the key concepts, diagrams, and exam requirements, with every explanation mirrored in Chinese to support bilingual learning.

需求与供给是市场经济的核心。在 CCEA IGCSE 经济学中，扎实掌握买卖双方如何相互作用，对于解释价格决定、市场结果和政府政策效果至关重要。本篇考点精讲将带你梳理关键概念、图示和考试要求，每个解释都配有对应的中文，助力双语学习。

1. The Basic Economic Problem | 基本经济问题

Every economy faces the basic economic problem of scarcity: unlimited wants but limited resources. This forces choices about what to produce, how to produce, and for whom to produce. Demand and supply are the mechanisms that help answer these questions in a market system.

每个经济体都面临稀缺这一基本经济问题：无限的欲望与有限的资源。这迫使社会必须就生产什么、如何生产以及为谁生产做出选择。在市场体系中，需求与供给正是帮助回答这些问题的机制。

In CCEA exams, you must be able to link scarcity to the need for allocation. The price mechanism uses demand and supply signals to allocate resources efficiently, without central planning.

在 CCEA 考试中，你必须能够将稀缺性与资源分配的需要联系起来。价格机制通过需求与供给信号实现资源高效配置，无需中央计划。

2. Demand: Definition and Law of Demand | 需求：定义与需求法则

Demand is the quantity of a good or service that consumers are willing and able to buy at various prices over a given time period, ceteris paribus. The law of demand states that, all else being equal, as the price of a good rises, the quantity demanded falls, and vice versa.

需求是指在一定时期内，在其他条件不变的前提下，消费者愿意并且能够购买的商品或服务的数量。需求法则指出，其他条件不变时，商品价格上升，需求量下降；价格下降，需求量上升。

This inverse relationship is shown by a downward-sloping demand curve. There are two reasons: the income effect (lower price increases purchasing power) and the substitution effect (consumers switch from relatively more expensive alternatives).

这种反向关系表现为一条向下倾斜的需求曲线。原因有二：收入效应（价格降低提升了购买力）和替代效应（消费者从相对更贵的替代品转向该商品）。

Demand curve: P ↑ → Qd ↓ (movement along the curve)

需求曲线：价格 ↑ → 需求量 ↓（沿曲线移动）

3. Determinants of Demand | 影响需求的因素

Factors other than price that shift the entire demand curve are called determinants of demand. An increase in demand shifts the curve to the right; a decrease shifts it to the left. Key determinants include:

影响需求曲线移动的价格以外的因素被称为需求的决定因素。需求增加使曲线向右平移；需求减少使曲线向左平移。关键因素包括：

Income: For normal goods, higher income increases demand; for inferior goods, it decreases demand.
收入： 对于正常商品，收入提高会增加需求；对于低档商品，收入提高会减少需求。
Prices of related goods: Substitutes (e.g., tea and coffee) – a rise in the price of one increases demand for the other. Complements (e.g., printers and ink) – a rise in the price of one reduces demand for the other.
相关商品价格： 替代品（如茶和咖啡）—— 一种商品价格上升会增加对另一种的需求。互补品（如打印机和墨盒）—— 一种商品价格上升会减少对另一种的需求。
Tastes and preferences: Advertising, fashion, or changes in consumer attitudes can shift demand.
品味与偏好： 广告、时尚或消费者态度的变化会使需求移动。
Population size and demographics: More consumers or changes in age structure affect market demand.
人口规模与结构： 消费者数量增加或年龄结构变化会影响市场需求。
Expectations of future prices: If consumers expect prices to rise, current demand may increase.
对未来价格的预期： 如果消费者预期价格上涨，当前需求可能增加。

4. Movements Along vs. Shifts of Demand Curve | 需求曲线上的移动与曲线的移动

It is critical in CCEA exams to distinguish between a movement along the demand curve and a shift of the demand curve. A change in the good’s own price causes a movement along the curve (extension or contraction). A change in any other determinant causes the entire curve to shift.

在 CCEA 考试中，区分需求曲线上的移动与需求曲线的移动至关重要。商品自身价格变化导致沿曲线的移动（延伸或收缩）。其他任何决定因素的变化则导致整条曲线的平移。

Change	Effect on curve	Terminology
Price of the good falls	Movement down along curve	Extension in demand
Price of the good rises	Movement up along curve	Contraction in demand
Increase in income (normal good)	Curve shifts right	Increase in demand
Fall in price of substitute	Curve shifts left	Decrease in demand

中文对应： 变化 | 对曲线的影响 | 术语

价格下跌 → 沿曲线向下移动 → 需求延伸；价格上涨 → 沿曲线向上移动 → 需求收缩；收入增加（正常商品）→ 曲线右移 → 需求增加；替代品价格下降 → 曲线左移 → 需求减少。

5. Supply: Definition and Law of Supply | 供给：定义与供给法则

Supply is the quantity of a good or service that producers are willing and able to offer for sale at various prices over a given time period, ceteris paribus. The law of supply states that, all else equal, as the price of a good rises, the quantity supplied increases, and as price falls, quantity supplied decreases.

供给是指在一定时期内，在其他条件不变的前提下，生产者愿意并且能够提供出售的商品或服务的数量。供给法则指出，其他条件不变时，商品价格上升，供给量增加；价格下降，供给量减少。

The supply curve slopes upward because higher prices provide an incentive for firms to produce more – it increases potential profit, and new firms may enter the market.

供给曲线向上倾斜，因为更高的价格为厂商提供了扩大生产的激励——这会增加潜在利润，并可能吸引新企业进入市场。

Supply curve: P ↑ → Qs ↑ (movement along the curve)

供给曲线：价格 ↑ → 供给量 ↑（沿曲线移动）

6. Determinants of Supply | 影响供给的因素

Factors that shift the supply curve are called determinants of supply. An increase in supply shifts the curve to the right; a decrease shifts it to the left. Important determinants include:

使供给曲线移动的因素被称为供给的决定因素。供给增加使曲线向右平移；供给减少使曲线向左平移。重要的决定因素包括：

Costs of production: Changes in wages, raw material prices, energy costs, or taxes. Lower costs increase supply (shift right).
生产成本： 工资、原材料价格、能源成本或税收的变化。成本降低会增加供给（曲线右移）。
Technology: Improvements in technology raise productivity and increase supply.
技术： 技术进步提高生产率，从而增加供给。
Government policies: Subsidies increase supply; indirect taxes (e.g., excise duty) decrease supply. Regulations may also affect costs.
政府政策： 补贴增加供给；间接税（如消费税）减少供给。法规也会影响成本。
Weather and natural factors: For agricultural products, good weather boosts supply; drought reduces it.
天气与自然因素： 对农产品而言，好天气增加供给；干旱减少供给。
Number of suppliers: More firms in the market increase total supply.
供应商数量： 市场中企业数量增多会使总供给增加。
Prices of related goods in production: If a farmer can grow wheat or barley, a rise in barley’s price may reduce the supply of wheat (joint supply or competitive supply).
生产中的相关商品价格： 如果农民可以种植小麦或大麦，大麦价格上涨可能减少小麦的供给（联合供给或竞争性供给）。

7. Movements Along vs. Shifts of Supply Curve | 供给曲线上的移动与曲线的移动

Just like demand, we must differentiate between a movement along the supply curve (caused only by a change in the good’s own price) and a shift of the supply curve (caused by changes in other determinants). A shift to the right is an increase in supply; a shift to the left is a decrease in supply.

与需求一样，我们必须区分供给曲线上的移动（仅由商品自身价格变化引起）和供给曲线的平移（由其他决定因素变化引起）。向右平移表示供给增加；向左平移表示供给减少。

Change	Effect on curve	Terminology
Increase in own price	Movement up along curve	Extension in supply
Decrease in own price	Movement down along curve	Contraction in supply
Fall in production costs	Curve shifts right	Increase in supply
Introduction of a tax	Curve shifts left	Decrease in supply

中文： 自身价格上升 → 沿曲线向上移动 → 供给延伸；自身价格下降 → 沿曲线向下移动 → 供给收缩；生产成本下降 → 曲线右移 → 供给增加；征税 → 曲线左移 → 供给减少。

8. Market Equilibrium | 市场均衡

Market equilibrium occurs where the demand and supply curves intersect. At this price (equilibrium price), the quantity demanded equals the quantity supplied. There is no shortage or surplus. Markets tend toward equilibrium naturally through the price mechanism.

市场均衡发生在需求曲线与供给曲线的交点处。在该价格（均衡价格）下，需求量等于供给量，不存在短缺或过剩。市场通过价格机制自然地趋向均衡。

If the price is above equilibrium, there is excess supply (surplus). Producers lower prices to clear stock, moving the market back to equilibrium. If the price is below equilibrium, there is excess demand (shortage). Buyers bid up the price, and the market moves to equilibrium.

如果价格高于均衡，就会出现供给过剩（剩余）。生产者降低价格以清理库存，市场回归均衡。如果价格低于均衡，就会出现需求过剩（短缺）。购买者抬高价格，市场回归均衡。

Equilibrium: Qd = Qs at P_e

均衡：在均衡价格 P_e 下，Qd = Qs

9. Changes in Equilibrium | 均衡的变化

When demand or supply shifts, the equilibrium price and quantity change. CCEA often asks you to analyse the effects of events such as a rise in income or a subsidy. Always consider both price and quantity outcomes and show them on a properly labelled diagram.

当需求或供给发生移动时，均衡价格和均衡数量随之改变。CCEA 考试常常要求你分析诸如收入增加或给予补贴等事件的影响。务必同时考虑价格和数量的结果，并在正确标注的图示中展示。

Example: An increase in demand (shift right) leads to a higher equilibrium price and a higher equilibrium quantity. An increase in supply (shift right) leads to a lower equilibrium price and a higher equilibrium quantity. If both curves shift simultaneously, the final outcome depends on the relative magnitude of the shifts.

示例：需求增加（曲线右移）导致均衡价格上升和均衡数量增加。供给增加（曲线右移）导致均衡价格下降和均衡数量增加。如果两条曲线同时移动，最终结果取决于移动的相对幅度。

Shift	Price change	Quantity change
Demand ↑	↑	↑
Demand ↓	↓	↓
Supply ↑	↓	↑
Supply ↓	↑	↓

中文对应： 需求 ↑ → 价格 ↑，数量 ↑；需求 ↓ → 价格 ↓，数量 ↓；供给 ↑ → 价格 ↓，数量 ↑；供给 ↓ → 价格 ↑，数量 ↓。

10. Price Elasticity of Demand (PED) – Basic Idea | 需求价格弹性（PED）基础概念

Price elasticity of demand measures how responsive quantity demanded is to a change in price. The formula is:

需求价格弹性衡量需求量对价格变化的反应程度。其公式为：

PED = % change in quantity demanded / % change in price

PED = 需求量变动百分比 ÷ 价格变动百分比

If the absolute value of PED > 1, demand is elastic (consumers are responsive to price changes). If PED < 1, demand is inelastic (consumers are less responsive). If PED = 1, it is unit elastic. PED = 0 is perfectly inelastic; PED = ∞ is perfectly elastic.

如果 PED 的绝对值大于 1，需求富有弹性（消费者对价格变化反应敏感）。如果 PED 小于 1，需求缺乏弹性（消费者反应不敏感）。PED = 1 为单位弹性。PED = 0 为完全无弹性；PED = ∞ 为完全弹性。

Determinants include the availability of substitutes, whether the good is a necessity or luxury, the proportion of income spent, and the time period. CCEA expects you to apply PED to real-world contexts, such as why a farmer’s revenue may fall after a good harvest if demand is inelastic.

决定因素包括替代品的可得性、商品是必需品还是奢侈品、支出占收入的比例以及时间期限。CCEA 期待你能将 PED 运用到实际情境中，例如，如果需求缺乏弹性，丰收后农民的收入反而可能下降。

11. Price Elasticity of Supply (PES) – Basic Idea | 供给价格弹性（PES）基础概念

Price elasticity of supply measures how responsive quantity supplied is to a change in price. The formula:

供给价格弹性衡量供给量对价格变化的反应程度。其公式为：

PES = % change in quantity supplied / % change in price

PES = 供给量变动百分比 ÷ 价格变动百分比

If PES > 1, supply is elastic; if PES < 1, supply is inelastic. Factors affecting PES include production time lag, availability of stocks, spare capacity, and the ease of switching production. For example, agricultural products often have inelastic supply in the short run because crops take time to grow.

如果 PES 大于 1，供给富有弹性；如果 PES 小于 1，供给缺乏弹性。影响 PES 的因素包括生产时滞、库存可得性、闲置产能以及转换生产的难易程度。例如，农产品在短期内的供给通常缺乏弹性，因为作物生长需要时间。

12. Exam Tips for CCEA | CCEA 考试技巧

To score high marks, always define terms precisely, use clear diagrams with labelled axes (price and quantity), and distinguish between movements and shifts. When analysing scenarios, state the determinant, show the shift on a graph, and explain the new equilibrium. Support your answers with real-life examples where possible. For elasticity, always calculate if data is given and interpret the value.

为获取高分，务必精确地定义术语，使用带有清晰坐标轴标注（价格和数量）的图示，并区分曲线的移动与沿曲线的移动。在分析情境时，要说明相关决定因素，在图形中展示移动，并解释新的均衡。尽可能用现实生活中的例子支撑答案。对于弹性问题，如果提供了数据，始终要进行计算并解释数值。

Common pitfalls include confusing a shift with a movement, mislabelling curves, or forgetting ceteris paribus. Remember that CCEA expects you to use economic terminology accurately. Practice drawing diagrams for both demand and supply scenarios until they become automatic.

常见误区包括混淆曲线平移与沿曲线移动、曲线标注错误或忘记“其他条件不变”的假设。请记住，CCEA 要求你准确使用经济学专业术语。反复练习绘制需求和供给场景的图示，直到形成条件反射。

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Demand and Supply in CCEA IGCSE Economics | IGCSE CCEA 经济：需求与供给 考点精讲