Price Elasticity of Supply Explained | A-Level 经济：供给的价格弹性解析

📚 Price Elasticity of Supply Explained | A-Level 经济：供给的价格弹性解析

Price elasticity of supply (PES) measures how responsive the quantity supplied of a good is to a change in its price. It is a key concept in A-Level economics because it helps explain why some markets react quickly to price changes while others are slow to adjust.

供给的价格弹性（PES）衡量的是商品供给量对其价格变动的反应程度。在 A-Level 经济学中，这是一个核心概念，因为它有助于解释为什么有些市场对价格变化反应迅速，而另一些市场却调整缓慢。

1. What Is Price Elasticity of Supply? | 什么是供给的价格弹性？

Price elasticity of supply is the percentage change in quantity supplied resulting from a percentage change in price. Because supply curves generally slope upward, PES is usually positive.

供给的价格弹性指的是价格变动百分之一所引起的供给量变动的百分比。由于供给曲线通常向右上方倾斜，PES 一般为正值。

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

The size of PES tells us how easy or difficult it is for producers to change output in response to price signals. A high PES means supply is flexible; a low PES means supply is rigid.

PES 的数值大小告诉我们，生产者在收到价格信号后是否容易调整产量。较高的 PES 表示供给灵活；较低的 PES 表示供给僵化。

2. The PES Formula and Its Interpretation | PES 公式及其解读

To calculate PES, we compare the percentage change in quantity supplied with the percentage change in price. The unit of measurement cancels out, so PES has no units.

计算 PES 时，我们比较供给量的百分比变化与价格的百分比变化。由于单位会互相抵消，PES 没有单位。

PES = (ΔQs ÷ Qs) ÷ (ΔP ÷ P)

The Greek letter Δ (delta) means “a change in”. If price and quantity supplied move in the same direction, PES is greater than zero. For normal goods and services, this always happens because a higher price creates a stronger incentive to supply more.

希腊字母 Δ（delta）表示“变化量”。当价格与供给量朝同一方向变动时，PES 大于零。对于正常的商品和服务，因为较高的价格会带来更强的供给激励，这种情况总是会出现。

When interpreting PES, remember that it measures responsiveness, not the actual change in output. Two goods with the same physical output change can have different PES values if their initial quantities differ.

在解读 PES 时，请记住它衡量的是反应程度，而不是产量的实际变化。两种商品即使产量的绝对变化相同，由于初始供给量不同，它们的 PES 也可能不同。

3. Degrees of Elasticity of Supply | 供给弹性的五种类型

In A-Level economics, we classify PES into five main cases. The most important distinction in exams is between elastic supply (PES > 1) and inelastic supply (PES < 1).

在 A-Level 经济学中，我们将 PES 分为五种主要情况。考试中最重要的区分是弹性供给（PES > 1）与缺乏弹性供给（PES < 1）。