KS3 Edexcel Economics: Formula & Theorem Quick Reference Handbook | KS3 Edexcel 经济：公式定理速查手册

📚 KS3 Edexcel Economics: Formula & Theorem Quick Reference Handbook | KS3 Edexcel 经济：公式定理速查手册

Economics is built on a foundation of simple yet powerful ideas – from the cost of a missed opportunity to the forces that shape every price you see. This revision handbook pulls together the essential formulas, graphs, and core theorems you need for KS3 Edexcel Economics, explained in a clear, paired English–Chinese format to help you revise quickly and confidently.

经济学建立在一系列简单却强大的思想之上——从错失机会的成本到塑造你所见每一种价格的力量。这份速查手册汇集了 KS3 Edexcel 经济学必需的关键公式、图形和核心定理，采用中英配对的方式清晰解读，助你快速、自信地复习。

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1. Scarcity and Opportunity Cost | 稀缺性与机会成本

Scarcity means resources are limited while wants are unlimited, forcing us to make choices. The true cost of any choice is its opportunity cost – the next best alternative forgone.

稀缺性意味着资源有限而欲望无限，迫使我们必须做出选择。任何选择的真正代价是其机会成本——即所放弃的次优选择。

Core Formula: Opportunity Cost = Value of the next best alternative given up.

核心公式：机会成本 = 所放弃的次优替代选项的价值。

When a student uses £5 to buy a notebook instead of a sandwich, the opportunity cost of the notebook is the satisfaction and nutrition the sandwich would have provided.

当学生用5英镑买笔记本而不是三明治时，笔记本的机会成本就是三明治原本能提供的饱腹感和营养。

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2. The Law of Demand | 需求定律

The Law of Demand states that, ceteris paribus, as the price of a good rises, the quantity demanded falls, and vice versa. This creates a downward‑sloping demand curve.

需求定律指出，在其他条件不变的情况下，商品价格上升，需求量下降，反之亦然。这形成一条向下倾斜的需求曲线。

Relationship: Price ↑ → Quantity Demanded ↓; Price ↓ → Quantity Demanded ↑

关系：价格 ↑ → 需求量 ↓；价格 ↓ → 需求量 ↑

A movement along the demand curve is caused by a change in the good’s own price, while a shift of the whole curve is caused by non‑price factors like income, tastes, or price of substitutes.

沿需求曲线的移动由商品自身价格变化引起，而整条曲线的平移则由收入、偏好或替代品价格等非价格因素引起。

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3. The Law of Supply | 供给定律

The Law of Supply says that, ceteris paribus, as the price of a good rises, the quantity supplied rises, because higher prices give producers an incentive to increase output. The supply curve slopes upward.

供给定律指出，在其他条件不变的情况下，商品价格上升，供给量增加，因为更高的价格激励生产者扩大产出。供给曲线向上倾斜。

Relationship: Price ↑ → Quantity Supplied ↑; Price ↓ → Quantity Supplied ↓

关系：价格 ↑ → 供给量 ↑；价格 ↓ → 供给量 ↓

Shifts in supply occur when there are changes in production costs, technology, taxes, or the number of sellers – anything that changes how much firms are willing and able to produce at each price.

当生产成本、技术、税收或卖家数量发生变化时，供给曲线平移——即任何改变企业在每个价格下愿意且能够提供的产量的因素。

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4. Market Equilibrium | 市场均衡

Market equilibrium happens when quantity demanded equals quantity supplied (Qd = Qs). There is no tendency for price to change at this point; the market clears.

市场均衡出现在需求量等于供给量（Qd = Qs）之时。此时价格没有变动趋势，市场出清。

Condition: Qd = Qs at a specific price P*

条件：在特定价格 P* 下 Qd = Qs

If price is above equilibrium, a surplus (excess supply) pushes price down. If price is below equilibrium, a shortage (excess demand) pushes price up. The invisible hand guides the market back to equilibrium.

若价格高于均衡，出现过剩（超额供给），价格下降。若价格低于均衡，出现短缺（超额需求），价格上升。无形之手引导市场回归均衡。

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5. Price Elasticity of Demand (PED) | 需求价格弹性

Elasticity measures how much quantity demanded responds to a change in price. The PED coefficient compares the percentage change in quantity demanded to the percentage change in price.

弹性衡量需求量对价格变化的反应程度。PED 系数比较需求量百分比变化与价格百分比变化。

PED = %ΔQd ÷ %ΔP

Interpreting PED values:
|PED| > 1: Elastic (sensitive to price, e.g. luxury goods)
|PED| < 1: Inelastic (less sensitive, e.g. necessities)
|PED| = 1: Unit elastic (proportional change)
|PED| = 0: Perfectly inelastic (quantity unchanged)
|PED| → ∞: Perfectly elastic (any price rise kills demand)

解读 PED 值：
|PED| > 1：富有弹性（对价格敏感，如奢侈品）
|PED| < 1：缺乏弹性（不敏感，如必需品）
|PED| = 1：单位弹性（同比例变动）
|PED| = 0：完全无弹性（量不变）
|PED| → ∞：完全弹性（价格稍涨需求归零）

Total revenue test: If demand is elastic, a price cut raises total revenue; if inelastic, a price cut lowers total revenue.

总收入测试：若需求富有弹性，降价增加总收入；若缺乏弹性，降价减少总收入。

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6. Price Elasticity of Supply (PES) | 供给价格弹性

Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It depends on how easily firms can adjust production.

供给价格弹性衡量供给量对价格变化的反应程度，取决于企业调整生产的难易程度。

PES = %ΔQs ÷ %ΔP

Key determinants: time period (longer run is more elastic), spare production capacity, availability of raw materials, and how easy it is to store the product.

关键决定因素：时间长短（长期更具弹性）、闲置产能、原材料可得性以及产品储存难易度。

PES > 1: elastic supply; PES < 1: inelastic supply. A perfectly inelastic supply curve is vertical (e.g. fixed number of seats in a stadium).

PES > 1：供给富有弹性；PES < 1：供给缺乏弹性。完全无弹性供给曲线为垂直线（如体育场固定座位数）。

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7. Consumer and Producer Surplus | 消费者与生产者剩余

Consumer surplus is the extra benefit buyers get when they pay less than what they were willing to pay. Producer surplus is the extra benefit sellers receive when they sell above their minimum acceptable price.

消费者剩余是买方支付低于意愿支付金额时获得的额外好处。生产者剩余是卖方以高于最低可接受价格售出时获得的额外收益。

Consumer surplus = area below the demand curve and above the market price.
Producer surplus = area above the supply curve and below the market price.

消费者剩余 = 需求曲线下方、市场价格上方的面积。
生产者剩余 = 供给曲线上方、市场价格下方的面积。

Total welfare (economic surplus) = consumer surplus + producer surplus. A competitive market in equilibrium maximises total surplus.

总福利（经济剩余）= 消费者剩余 + 生产者剩余。竞争市场在均衡时最大化总剩余。

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8. Production Possibility Frontier (PPF) | 生产可能性边界

A PPF shows the maximum combinations of two goods an economy can produce with available resources and technology. Points on the curve are efficient, inside are inefficient, and outside are unattainable currently.

生产可能性边界（PPF）展示一个经济体利用现有资源和技术所能生产的两种商品的最大组合。曲线上的点效率高，内部的点效率低，外部的点目前无法达到。

Opportunity cost on the PPF: The slope of the PPF represents the opportunity cost of producing one more unit of the good on the horizontal axis, measured in units of the good on the vertical axis forgone.

PPF 上的机会成本：PPF 的斜率代表多生产一单位横轴商品的机会成本，用放弃的纵轴商品数量衡量。

A straight-line (linear) PPF indicates constant opportunity cost. A bowed-outward (concave) PPF implies increasing opportunity cost as resources are not equally suited to all types of production.

直线 PPF 表示机会成本不变。向外弯曲（凹向原点）的 PPF 表明机会成本递增，因为资源并非同等适用于所有生产类型。

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9. Government Intervention: Indirect Taxes | 政府干预：间接税

When the government imposes a per‑unit tax on a good, the supply curve shifts vertically upwards by the amount of the tax. The tax drives a wedge between the price consumers pay and the price producers receive.

当政府对商品征收从量税时，供给曲线向上垂直平移税额的幅度。税收在消费者支付价格与生产者到手价格之间打入一个楔子。

Key relationships:
Price paid by consumers (Pd) = Price received by producers (Ps) + Tax per unit
Tax revenue = Tax per unit × Quantity sold after tax
Tax burden is shared between consumers and producers depending on PED and PES: the more inelastic side bears a larger share.

关键关系：
消费者支付价格 (Pd) = 生产者到手价格 (Ps) + 单位税额
税收收入 = 单位税额 × 税后销售量
税收负担根据 PED 和 PES 由消费者和生产者分担：弹性更低的一方承担更大份额。

An ad valorem tax (e.g. VAT at 20%) causes a pivotal shift in supply, making the gap between Pd and Ps larger at higher prices.

从价税（如20%增值税）导致供给曲线旋转式平移，价格越高 Pd 与 Ps 之间的差距越大。

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10. Government Intervention: Subsidies | 政府干预：补贴

A subsidy is a payment from the government to producers that lowers their costs of production. The supply curve shifts vertically downwards by the amount of the subsidy per unit.

补贴是政府给予生产者的支付，降低其生产成本。供给曲线向下垂直平移单位补贴额的幅度。

Key relationships:
Price received by producers = Price paid by consumers + Subsidy per unit
Subsidy cost to the government = Subsidy per unit × Quantity consumed after subsidy
Both consumers and producers benefit, with the more inelastic side gaining a larger advantage.

关键关系：
生产者到手价格 = 消费者支付价格 + 单位补贴额
政府补贴成本 = 单位补贴额 × 补贴后消费量
消费者和生产者均受益，弹性更低的一方获得更大优势。

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11. The Circular Flow of Income | 收入循环流动模型

The simple circular flow model shows that in an economy without government or foreign trade, total spending by households equals total income earned by firms, which in turn equals the total value of output.

简单循环流动模型显示，在没有政府和对外贸易的经济中，家庭总支出等于企业所得总收入，进而等于总产出价值。

Flows: Households provide factors of production (labour, land, capital, entrepreneurship) to firms in exchange for factor income (wages, rent, interest, profit). Households spend this income on goods and services produced by firms.

流动：家庭向企业提供生产要素（劳动、土地、资本、企业家才能），换取要素收入（工资、租金、利息、利润）。家庭用收入购买企业生产的商品和服务。

Equilibrium condition: Withdrawals (savings, taxes, imports) must equal injections (investment, government spending, exports) for the economy to be stable.

均衡条件：漏出（储蓄、税收、进口）必须等于注入（投资、政府支出、出口），经济才能保持稳定。

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12. Key Graph‑based Theorems Summary | 核心图形定理小结

Visualising economic relationships is critical. Below are the fundamental graphs you must recognise, with their main messages.

将经济关系可视化至关重要。以下是你必须识别的核心图形及其主要含义。

Graph	Key Insight
Demand & Supply	Equilibrium where the two curves cross; price allocates scarce goods.
PPF	Opportunity cost, efficiency, and the potential for economic growth.
PED & PES	Slope steepness reflects responsiveness; not the same as slope alone.
Tax wedge	Deadweight loss from reduced trade; burden falls more on the inelastic side.
Circular flow	Every pound spent becomes a pound of income; leakages and injections balance.

Remember, memorising the diagrams is not enough – you need to be able to explain the economic stories they tell.

记住，只背图形是不够的——你需要能解释它们所讲述的经济故事。

Published by TutorHao | Economics Revision Series | aleveler.com

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