The Law of Supply

Active learning works for this topic because price elasticity requires students to move from abstract formulas to concrete decision-making. Calculating PED and PES in real-world settings helps students see how businesses and governments actually use these numbers. Stations and debates make the abstract concept of responsiveness tangible and memorable.

• Secondary 4
• Economics
• 3 activities
• 30 min–45 min

Learning Objectives

1. Explain the direct relationship between price and quantity supplied, citing the profit motive.
2. Analyze how changes in input costs, technology, and number of sellers shift the supply curve.
3. Predict the impact of government subsidies or taxes on the supply of a product.
4. Calculate the change in quantity supplied given a price change and a supply schedule.

Stations Rotation

⏱ 40 min·Small Groups

Stations Rotation: The Elasticity Lab

Set up stations with different products (e.g., salt, a specific brand of sneakers, electricity, and a luxury watch). Students rotate in groups to discuss and rank these items from most inelastic to most elastic, justifying their choices based on factors like substitutes and necessity.

Prepare & details

Explain the direct relationship between price and quantity supplied.

Facilitation Tip: During The Elasticity Lab, circulate to ensure students are using the midpoint formula correctly and not just estimating elasticity by looking at the graph.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Formal Debate

⏱ 45 min·Whole Class

Formal Debate: Taxing the Inelastic

Assign students to represent either the Ministry of Finance or a consumer rights group. They debate whether the government should increase taxes on goods with inelastic demand (like petrol). They must use the concept of PED to argue how the tax will affect government revenue and consumer behavior.

Prepare & details

Analyze how changes in production costs affect the supply curve.

Facilitation Tip: In Structured Debate: Taxing the Inelastic, assign roles clearly and provide a timer so students stay focused on the economic reasoning, not just the debate format.

Setup: Two teams facing each other, audience seating for the rest

Materials: Debate proposition card, Research brief for each side, Judging rubric for audience, Timer

• Analyze
• Evaluate
• Create
• Self-Management
• Decision-Making

Inquiry Circle

⏱ 30 min·Small Groups

Inquiry Circle: Revenue Riddles

Give groups scenarios where a firm wants to increase its total revenue. They are given the PED of their product and must decide whether to raise or lower prices. They present their 'business plan' with a graph showing the relationship between price changes and total revenue.

Prepare & details

Predict the impact of technological advancements on the supply of a product.

Facilitation Tip: For Revenue Riddles, group students heterogeneously so stronger calculators can guide peers through the reasoning process.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Teaching This Topic

Experienced teachers approach this topic by starting with simple, relatable goods to build intuition before introducing formulas. They emphasize that elasticity is about percentage changes, not absolute changes, and avoid relying solely on graphs. Using real-world examples, like luxury versus necessity goods, helps students internalize the concept. Teachers should also address common confusion between elasticity and slope early, using hands-on calculations to demonstrate that elasticity varies along a linear curve.

What to Expect

Successful learning looks like students confidently distinguishing between elastic and inelastic goods, explaining why revenue rises or falls with price changes, and connecting elasticity to real business strategies. They should use correct terminology and justify their reasoning with calculations. Misconceptions about slope versus elasticity should be resolved.

Watch Out for These Misconceptions

Common Misconception

During The Elasticity Lab, watch for students assuming the slope of the demand curve determines elasticity at every point.

What to Teach Instead

During The Elasticity Lab, have students calculate PED at three different points on the same demand curve and compare the results to show that elasticity changes even when the slope stays constant.

Common Misconception

During Structured Debate: Taxing the Inelastic, watch for students thinking inelastic demand means consumers ignore price entirely.

What to Teach Instead

During Structured Debate: Taxing the Inelastic, provide examples like addictive goods or life-saving medications and ask students to calculate small but meaningful changes in quantity demanded to illustrate relative unresponsiveness.

Assessment Ideas

Quick Check

After The Elasticity Lab, present students with a new hypothetical scenario: 'The price of gasoline drops sharply. What is likely to happen to the quantity of gasoline supplied by oil companies?' Ask students to write their answer and one sentence explaining their reasoning based on the Law of Supply.

Discussion Prompt

After Structured Debate: Taxing the Inelastic, pose the question: 'Imagine a new, cheaper method for producing face masks is invented. How will this affect the supply curve for face masks?' Facilitate a class discussion, calling on students to explain the role of technology in shifting the supply curve.

Exit Ticket

After Collaborative Investigation: Revenue Riddles, provide students with a simple supply schedule for coffee. Ask them to calculate the quantity supplied at two different prices. Then, ask them to identify one factor (other than price) that could cause the entire supply curve to shift.

Extensions & Scaffolding

• Challenge students who finish early to create a scenario where a producer faces a price increase and decide whether to raise or lower production based on PES values.
• For students who struggle, provide pre-calculated examples of PED with clear step-by-step explanations before they attempt calculations themselves.
• Deeper exploration: Ask students to research a real company’s pricing strategy and analyze it using elasticity concepts from the lesson.

Key Vocabulary

Law of Supply	States that, all else being equal, the quantity supplied of a good increases when the price of that good increases. This is driven by the producer's desire for higher profits.
Quantity Supplied	The specific amount of a good or service that producers are willing and able to offer for sale at a particular price during a specific period.
Supply Curve	A graphical representation showing the relationship between the price of a good or service and the quantity supplied, typically sloping upwards.
Determinants of Supply	Factors other than price that can cause a change in supply, leading to a shift of the entire supply curve. These include input costs, technology, and expectations.