Price elasticity of supply

1. Overview

Price Elasticity of Supply (PES) measures the responsiveness of the quantity supplied of a good or service to a change in its price. It quantifies how easily and quickly producers can change their output levels when market prices fluctuate. For a firm, high elasticity means they can rapidly increase production to capture higher profits when prices rise. For a government, understanding PES is essential for predicting how industries will respond to taxes, subsidies, or changes in national demand.

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Key Definitions

• Price Elasticity of Supply (PES): A numerical measure of the degree of responsiveness of the quantity supplied of a product to a change in its price.
• Elastic Supply: A situation where the percentage change in quantity supplied is greater than the percentage change in price (PES > 1).
• Inelastic Supply: A situation where the percentage change in quantity supplied is less than the percentage change in price (PES < 1).
• Unitary Elastic Supply: A situation where the percentage change in quantity supplied is exactly equal to the percentage change in price (PES = 1).
• Perfectly Inelastic Supply: A situation where the quantity supplied remains constant regardless of any change in price (PES = 0).
• Perfectly Elastic Supply: A situation where producers are willing to supply an infinite amount at a specific price, but nothing at all if the price falls even slightly (PES = $\infty$).
• Time Period: The window of time available for a producer to adjust their inputs (land, labor, capital) to change output levels.
• Stock (Inventories): Reserves of raw materials or finished goods held by a firm that can be released into the market immediately.

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Core Content

The Concept of PES

PES is based on the Law of Supply, which states that as price rises, quantity supplied rises. However, the Law of Supply does not tell us by how much supply will rise. PES provides this specific measurement.

The Numerical Values of PES:

Value	Classification	Meaning	Curve Shape
PES = 0	Perfectly Inelastic	Supply cannot change at all (e.g., stadium seats).	Vertical line
0 < PES < 1	Inelastic	Supply is unresponsive to price changes.	Steep curve
PES = 1	Unitary Elastic	Supply changes at the same rate as price.	Diagonal through origin
1 < PES < $\infty$	Elastic	Supply is highly responsive to price changes.	Shallow (flat) curve
PES = $\infty$	Perfectly Elastic	Supply is infinite at one price.	Horizontal line

Worked Example 1 — Calculating and Interpreting PES

Question: A manufacturer of wooden chairs increases the price of a standard chair from US$50 to US$60. In response, the factory increases its weekly production from 200 chairs to 220 chairs. Calculate the Price Elasticity of Supply and state whether the supply is elastic or inelastic.

Step 1: Calculate % change in Price $$\frac{60 - 50}{50} \times 100 = 20%$$

Step 2: Calculate % change in Quantity Supplied $$\frac{220 - 200}{200} \times 100 = 10%$$

Step 3: Apply the PES Formula $$PES = \frac{10%}{20%} = 0.5$$

Answer: The PES is 0.5. Since 0.5 is less than 1, the supply of wooden chairs is inelastic. This suggests the firm faces some constraints in increasing production quickly, such as a lack of spare raw materials or limited machinery.

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Factors Determining PES

The elasticity of supply depends on how flexible a firm’s production process is. Use these Chains of Reasoning for exam answers:

1. Time Period

• The Short Run: At least one factor of production (usually capital/land) is fixed. It is difficult to build a new factory or find more land instantly.
• Chain of Reasoning: Price of wheat rises $\rightarrow$ Farmer wants to grow more $\rightarrow$ Crops take 6 months to grow and land is already planted $\rightarrow$ Supply cannot increase immediately $\rightarrow$ PES is inelastic.
• The Long Run: All factors of production are variable. Firms can expand factories and new firms can enter the market.
• Chain of Reasoning: Price of wheat stays high for years $\rightarrow$ Farmer buys neighboring land and more tractors $\rightarrow$ Total output increases significantly $\rightarrow$ PES is elastic.

2. Availability of Stocks (Inventories)

• Chain of Reasoning: Price of smartphones rises $\rightarrow$ Manufacturer holds large stocks in a warehouse $\rightarrow$ Goods can be shipped to shops within 24 hours $\rightarrow$ Quantity supplied responds quickly $\rightarrow$ PES is elastic.
• Contrast: Perishable goods (like fresh milk) cannot be stocked easily, making their supply inelastic.

3. Spare Capacity

• Chain of Reasoning: Price of steel rises $\rightarrow$ A steel mill is currently only using 60% of its machinery $\rightarrow$ The firm can immediately increase shifts and turn on idle machines $\rightarrow$ Output rises without needing new investment $\rightarrow$ PES is elastic.

4. Ease of Switching Resources (Mobility of Factors)

• Chain of Reasoning: Price of printed textbooks rises $\rightarrow$ A printing press can easily switch from printing magazines to printing textbooks using the same machines and paper $\rightarrow$ Production shifts quickly to the higher-priced good $\rightarrow$ PES is elastic.

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Worked Example 2 — Factors Affecting PES

Question: Explain why the supply of new housing in a major city is likely to be price inelastic.

Model Answer: The supply of new housing is likely to be price inelastic (PES < 1) for several reasons:

1. Time Period: Construction is a lengthy process. Even if house prices rise, it takes years to acquire land, obtain legal planning permissions, and complete the physical building process. Therefore, supply cannot respond quickly to price signals.
2. Availability of Factors: There may be a shortage of skilled labor (e.g., bricklayers, architects) or specific raw materials. If these resources are not readily available, developers cannot increase the quantity supplied even if they want to.
3. Limited Land: In major cities, the supply of available land is often fixed. Since land is a necessary factor of production for housing, the inability to find new plots makes the supply curve very steep (inelastic).

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The Role of PES in Decision Making

For Firms:

• Goal: Firms want to make their supply as elastic as possible.
• Why?: High elasticity allows a firm to be "agile." If prices rise, they can grab market share and maximize profit. If prices fall, they can quickly reduce production to avoid wasting money on unsold stock.
• How?: Firms improve elasticity by:
  • Investing in multi-purpose technology (ease of switching).
  • Training workers in multiple roles (labor flexibility).
  • Improving storage systems (increasing stocks).

For Governments:

• Subsidies: If a government gives a subsidy to an industry with inelastic supply (e.g., specialized medical research), the quantity produced will not increase much. The subsidy might just result in higher wages for the existing researchers rather than more research being done.
• Expansionary Policy: If the government wants to increase the supply of affordable housing, they must address the causes of inelasticity (e.g., by simplifying planning laws) rather than just relying on price incentives.

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Extended Content (Extended Only)

Evaluation: The Impact of PES on Price Stability The elasticity of supply determines how volatile (unstable) prices are in a market when demand shifts.

• Inelastic Supply + Demand Shift: If demand for oil increases and supply is inelastic (because it takes years to drill new wells), the result is a massive spike in price with only a tiny increase in quantity. This leads to price instability.
• Elastic Supply + Demand Shift: If demand for digital music downloads increases and supply is elastic (because copies can be made instantly), the quantity supplied increases to meet the demand with almost no change in price. This leads to price stability.

Long-run Implications: In the long run, supply is almost always more elastic than in the short run. This means that "shocks" to the economy (like a sudden shortage of a resource) usually cause high price pain in the short term, but as producers adapt over time, prices eventually stabilize as supply becomes more responsive.

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Key Equations

1. The PES Formula: $$PES = \frac{% \text{ Change in Quantity Supplied}}{% \text{ Change in Price}}$$

2. Calculating Percentage Change: $$% \text{ Change} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100$$

3. Interpreting the Result:

• PES > 1: Elastic
• PES < 1: Inelastic
• PES = 1: Unitary Elastic
• PES = 0: Perfectly Inelastic
• PES = $\infty$: Perfectly Elastic

Note: PES is always a positive number. If your calculation results in a negative number, you have likely confused the formula with Price Elasticity of Demand (PED).

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Common Mistakes to Avoid

• ❌ Confusing PES with the Law of Supply: The Law of Supply says direction (price up, supply up). PES says magnitude (how much supply goes up).
• ❌ Confusing Supply with Quantity Supplied: PES measures the responsiveness of quantity supplied (movement along the curve) to a change in price. It is not about the supply curve shifting left or right.
• ❌ Misidentifying the "Time" factor: Don't just say "time." Specify that in the short run, factors are fixed (inelastic), while in the long run, all factors are variable (elastic).
• ❌ Thinking PES depends on consumers: PES is entirely about producers. If a question asks why supply is inelastic, do not talk about whether consumers like the product. Talk about production constraints like factory size, stocks, or labor skills.

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Exam Tips

• The "I" Trick: When looking at a graph, remember that Inelastic supply curves are steep and look like the letter "I".
• Agricultural Context: If an exam question mentions farming, crops, or raw commodities, your first thought should be Inelastic Supply due to the biological growth time.
• Show Your Workings: In Paper 2, a calculation question is usually worth 2 marks. Even if your final PES number is wrong, you will get 1 mark for correctly stating the formula or calculating the percentage changes.
• Use the "Chain of Reasoning": For 4-mark or 6-mark "Explain" questions, don't just list factors. Use the "$\rightarrow$" logic shown in Section 3 to show how a factor leads to a specific elasticity.
• Check the Units: Ensure you are using the percentage change, not the absolute change in dollars or units.

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Exam-Style Questions

Practice these original exam-style questions to test your understanding. Each question mirrors the style, structure, and mark allocation of real Cambridge 0455 papers.

Exam-Style Question 1 — Short Answer [6 marks]

Question:

A local farm increases the supply of organic blueberries from 400 kg to 500 kg per week when the price increases from US$5to US$6 per kg.

(a) Calculate the price elasticity of supply (PES) for organic blueberries. [3]

(b) Explain what the value of PES calculated in part (a) indicates about the responsiveness of supply to price changes. [3]

Worked Solution:

(a)

1. Calculate the percentage change in quantity supplied: $ \frac{500 - 400}{400} \times 100 = 25%$ [Calculate the percentage change in quantity supplied]

2. Calculate the percentage change in price: $ \frac{6 - 5}{5} \times 100 = 20%$ [Calculate the percentage change in price]

3. Calculate the PES: $ PES = \frac{% \Delta Qs}{% \Delta P} = \frac{25}{20} = 1.25 $ [Divide the percentage change in quantity supplied by the percentage change in price]

$\boxed{PES = 1.25}$

How to earn full marks: Write down the formula, show your workings clearly, and state the final answer with the correct value.

(b)

1. The PES value of 1.25 indicates that the supply of organic blueberries is elastic. [B1] [State that the supply is elastic]

2. This means that the quantity supplied is quite responsive to price changes. [B1] [Explain the meaning of elastic supply]

3. A 1% change in price leads to a greater than 1% change in quantity supplied (specifically, a 1.25% change). [B1] [Relate the PES value to the responsiveness of supply]

How to earn full marks: State whether supply is elastic or inelastic, explain what that means in terms of responsiveness, and link it back to the calculated PES value.

Common Pitfall: Remember that PES is a ratio of percentage changes. Don't mix up the percentage change in quantity supplied and the percentage change in price when calculating the PES value. Also, be sure to interpret the PES value correctly – values greater than 1 indicate elastic supply, while values less than 1 indicate inelastic supply.

Exam-Style Question 2 — Short Answer [4 marks]

Question:

(a) Define 'price elasticity of supply'. [2]

(b) State two factors that can influence the price elasticity of supply of a product. [2]

Worked Solution:

(a)

1. Price elasticity of supply (PES) measures the responsiveness of the quantity supplied of a good or service to a change in its price. [B2] [Correct definition of PES, including both price and quantity supplied]

How to earn full marks: Include the key words "responsiveness", "quantity supplied", and "change in price" in your definition.

(b)

1. Availability of stocks/inventory [B1] [State one factor that affects PES]

2. Production time [B1] [State another factor that affects PES]

How to earn full marks: Give two distinct factors that affect how quickly or easily firms can change production levels.

Common Pitfall: Make sure your definition of PES clearly states that it measures the responsiveness of quantity supplied to a change in price. Don't confuse it with price elasticity of demand! When listing factors, think about what makes it easier or harder for producers to quickly change their output.

Exam-Style Question 3 — Extended Response [8 marks]

Question:

A firm producing electric scooters is considering increasing its production capacity.

(a) Explain how the time period can influence the price elasticity of supply of electric scooters. [4]

(b) Analyse how an increase in the price of lithium used in electric scooter batteries might affect the supply of electric scooters. [4]

Worked Solution:

(a)

1. In the short run, the firm may have limited ability to increase production quickly due to fixed factors of production like factory size or the number of assembly lines. [B1] [Explain short-run constraints]

2. This would result in a relatively inelastic supply, as the quantity supplied cannot increase much in response to a price rise. [B1] [Link short-run constraints to inelastic supply]

3. In the long run, the firm has more flexibility to adjust its production capacity. They can invest in new assembly lines, build new factories, or train more skilled workers. [B1] [Explain long-run flexibility]

4. This leads to a more elastic supply, as the firm can significantly increase the quantity supplied in response to a price rise. [B1] [Link long-run flexibility to elastic supply]

How to earn full marks: Clearly distinguish between short run (fixed factors) and long run (all factors variable), and link each to the elasticity of supply.

(b)

1. An increase in the price of lithium will increase the cost of production for electric scooters. [B1] [State the impact on production costs]

2. This will make it less profitable for the firm to produce electric scooters at the current price. [B1] [Explain the impact on profitability]

3. As a result, the firm will likely reduce the quantity of electric scooters it is willing to supply at each price level, leading to a decrease in supply. [B1] [Explain the shift in the supply curve]

4. This is shown as a leftward shift of the supply curve for electric scooters. [B1] [Refer to a leftward shift of the supply curve]

How to earn full marks: Explain how the cost increase affects profitability, and how that leads to a decrease in supply (leftward shift of the curve).

Common Pitfall: When discussing time periods, clearly distinguish between the short run (when at least one factor of production is fixed) and the long run (when all factors are variable). Also, remember that an increase in the cost of production decreases supply, shifting the supply curve to the left.

Exam-Style Question 4 — Extended Response [12 marks]

Question:

A country that is a major exporter of manufactured goods is experiencing a shortage of a key raw material.

(a) Explain how the shortage might affect the price elasticity of supply for different manufactured products, such as textiles and electronics. [6]

(b) Discuss the potential advantages and disadvantages for the country's economy of having a low price elasticity of supply for its manufactured exports during the shortage. [6]

Worked Solution:

(a)

1. For textiles, production might be less affected if alternative materials can be used or if the key raw material represents a smaller proportion of total costs. [B1] [Explain the impact of shortage on textiles]

2. This means the supply of textiles might be relatively more elastic, as firms can adjust production more easily in response to price changes. [B1] [Link material substitution to elastic supply of textiles]

3. For electronics, if the shortage involves a specialized component with no readily available substitutes, production could be severely limited. [B1] [Explain the impact of shortage on electronics]

4. The supply of electronics would likely be very inelastic, as firms cannot easily increase production even if prices rise significantly. [B1] [Link lack of substitutes to inelastic supply of electronics]

5. The availability of stockpiles of the raw material can also influence PES in the short run. Firms with larger stockpiles will have a more elastic supply in the short run. [B1] [Explain the influence of stockpiles]

6. Government intervention, such as rationing the raw material or providing subsidies, could also affect the PES for both products. For example, subsidies could make the supply of electronics more elastic. [B1] [Introduce the influence of government intervention]

How to earn full marks: Compare and contrast how the shortage affects different industries, considering factors like substitutes, stockpiles, and government intervention.

(b)

1. Advantages of low PES: Higher export revenue. With an inelastic supply, the country cannot increase exports significantly even if global prices rise due to the shortage. [B1] [State one advantage: higher export revenue]

2. This can lead to higher export revenue if global demand remains relatively constant, benefiting the country's trade balance in the short term. [B1] [Explain how higher export revenue benefits the trade balance]

3. Disadvantages of low PES: Reduced export volume. A low PES means that the country cannot take full advantage of potential export opportunities if global demand increases significantly. [B1] [State one disadvantage: reduced export volume]

4. This limits the potential gains from trade and could lead to a loss of market share to countries with more elastic supply. [B1] [Explain how reduced export volume harms market share]

5. Furthermore, domestic industries that rely on the exported manufactured goods as inputs may face higher costs and reduced competitiveness. [B1] [State another disadvantage: higher costs for domestic industries]

6. Overall: While higher export revenue in the short term might seem beneficial, the disadvantages of a low PES, such as lost export opportunities, reduced competitiveness of downstream industries, likely outweigh the advantages in the long run. The country needs to diversify its sources of raw materials and invest in research and development to find substitutes to improve the PES of its manufactured exports. [B1] [Reach a justified conclusion]

How to earn full marks: Present both advantages and disadvantages with clear explanations, and then reach a well-reasoned conclusion about the overall impact.

Common Pitfall: When discussing the advantages and disadvantages of low PES, consider both the short-term and long-term effects. While higher export revenue might seem appealing initially, the inability to respond to increased demand can have negative consequences for the economy in the long run. Also, think about the impact on other industries within the country.