Unit Overview
Supply and Demand
AP MicroeconomicsΒ· 5 min read π 20-25% of total AP Microeconomics exam score
1. Unit at a Glance
This unit builds step-by-step from basic definitions to applied policy analysis. We start by separating buyer (demand) and seller (supply) behavior to understand what drives each curve, then combine them to explain how market prices and quantities are determined. Next, we explore elasticity, which measures how responsive buyers and sellers are to changes in prices, a critical tool for predicting market outcomes after shocks or policy changes. We then extend the model to measure social welfare, analyze the impacts of common government interventions, and end with applications to international trade policy.
Below are the 8 sub-topics that make up this unit:
Demand
Learn the law of demand, determinants of demand, and how to identify shifts vs. movements along the demand curve.
β β± 6 min
Supply
Cover the law of supply, determinants of supply, and how to interpret shifts vs. movements along the supply curve.
β β± 5 min
Price Elasticity of Demand
Calculate and interpret price elasticity of demand, and its relationship to total revenue for firms.
β β β± 7 min
Other Elasticities
Learn price elasticity of supply, income elasticity, and cross-price elasticity of demand.
β β β± 6 min
Market Equilibrium, Disequilibrium, and Changes in Equilibrium
Combine supply and demand to find equilibrium, and predict how shifts change equilibrium price and quantity.
β β β± 8 min
Consumer and Producer Surplus
Measure consumer and producer welfare, and calculate total surplus in competitive markets.
β β β β± 6 min
Government Intervention: Price Controls and Taxes
Analyze how price ceilings, price floors, and taxes impact market outcomes and social welfare.
β β β β± 10 min
International Trade and Public Policy
Evaluate the welfare effects of free trade and trade barriers like tariffs and quotas.
β β β β± 8 min
2. Common Pitfalls
Wrong move:
Confusing a shift in the demand/supply curve with a movement along the curve.
Why:
Only changes to the non-price determinants of demand/supply cause curves to shift; price changes only cause movements along existing curves.
Correct move:
Always check what is driving the change: price changes cause movements, all other factors cause shifts.
Wrong move:
Equating the slope of a linear demand curve to its elasticity.
Why:
Elasticity is percentage change, which varies along a linear demand curve, even with a constant slope.
Correct move:
Calculate elasticity for each interval or point separately, do not rely on slope alone.
Wrong move:
Assuming all market intervention makes consumers better off.
Why:
Many policies create unintended consequences like shortages, surpluses, and deadweight loss that harm some groups.
Correct move:
Always analyze both winners and losers when evaluating government policy in markets.
3. Quick Reference Cheatsheet
Concept | Key Formula / Rule |
|---|---|
Price Elasticity of Demand | |
Total Revenue Test | If : price and TR move opposite; If : price and TR move same direction |
Cross-Price Elasticity | Complements have negative ; substitutes have positive |
Consumer Surplus | Area below the demand curve, above the market price |
Producer Surplus | Area above the supply curve, below the market price |
Tax Incidence | The more inelastic side of the market bears the majority of the tax burden |
Tariff Welfare Effect | Tariffs raise government revenue but create net deadweight loss for the economy |
What's Next
Start your study of this unit with the first sub-topic on Demand to build your foundational knowledge of buyer behavior. Once you complete all 8 sub-topics in this unit, you will move on to the next unit covering production, costs, and perfect competition, where you will deepen your understanding of firm behavior in competitive markets.