Competitive market equilibrium: notes and practice questions
- This topic explains how demand and supply interact to determine equilibrium in competitive markets.
- Market equilibrium occurs where quantity demanded equals quantity supplied.
- Shifts in demand or supply curves lead to new equilibria, creating temporary shortages or surpluses.
- The price mechanism allocates resources through its signalling, incentive, and rationing functions.
- Consumer surplus is the benefit consumers receive above the price paid.
- Producer surplus is the benefit producers receive above the cost of production.
- Social/community surplus is the sum of consumer surplus and producer surplus.
- Allocative efficiency is achieved when marginal social benefit (MSB) equals marginal social cost (MSC), maximizing social/community surplus.
How it is examined
The most-used diagram in the whole course. At HL the surplus calculation is a Paper 3 staple and is worth 2 marks with working and units required. At both levels the equilibrium diagram is the vehicle for Paper 2 parts (c) to (f).
- Demand and supply curves forming a market equilibrium. (AO4)
- Shifting the demand and supply curves to produce a new equilibrium, with reference to excess demand (shortage) and excess supply (surplus). (AO2, AO4)
- The functions of the price mechanism: resource allocation through signalling and incentive, and rationing. (AO2)
- Consumer surplus and producer surplus. (AO2, AO4)
Calculating consumer surplus and producer surplus from a diagram. (AO4)
Guiding questions
- How does a market allocate resources, and what does it mean to say it does so efficiently?
Linking questions
- Allocative efficiency defined here is the benchmark that 2.8 and 2.11 measure failure against.
- Welfare loss in 2.8 (HL calculation) is read off a diagram using the same skill.
- Consumer and producer surplus reappear in the tariff, quota and subsidy diagrams of 4.2.
Practice questions
5 questions · 1 medium · 4 hardQuestion 1
MediumPaper 1 · no calculator25 marksGovernments intervene in markets to correct market failures and to influence the consumption of certain goods and services.
Explain one policy that could be used to correct a market failure and one policy that could be used to influence consumption.
Using real-world examples, evaluate the effectiveness of a government imposing a maximum price (price ceiling) on a particular good or service.
For the first policy, think about externalities. What kind of policies can address the difference between private costs/benefits and social costs/benefits? For the second policy, consider merit and demerit goods. How can a government encourage or discourage their consumption?
Start by explaining how a price ceiling works using a diagram. Then, consider its effects on different stakeholders (consumers, producers, government). For your evaluation, think about the intended goals of the policy versus its unintended consequences, such as shortages and black markets. Use a specific real-world example, like rent control or a cap on fuel prices, to support your arguments.
Question 2
HardPaper 1 · no calculator25 marks(a) Explain two non-price determinants that could decrease the market demand for a good.
(b) Using real-world examples, evaluate the view that imposing a price ceiling will always be beneficial for an economy.
Start by defining 'demand'. Then, identify two factors, other than the good's own price, that would cause consumers to want to buy less of it at any given price. For each factor, explain the mechanism through which it reduces demand. Illustrate this with a diagram showing a shift in the demand curve.
Define a price ceiling and explain its purpose. Use a diagram to show how a price ceiling set below the equilibrium price creates a shortage. Discuss the intended benefits, such as affordability for consumers. Then, critically evaluate the potential negative consequences, such as shortages, black markets, and reduced producer incentives. The command term 'evaluate' requires you to make a judgement, supported by real-world examples (e.g., rent controls, price caps on food or fuel). Consider the word 'always' in your final judgement.
Question 3
HardPaper 1 · no calculator25 marks(a) Explain how an increase in the price of gasoline (petrol) might affect the price and output of electric vehicles and of home charging stations.
(b) Using real-world examples, evaluate the view that imposing an indirect tax on gasoline (petrol) is the most effective way for a government to reduce air pollution from road transport.
Start by defining substitute and complement goods. Then, consider the relationship between gasoline-powered cars and electric vehicles. How does a change in the cost of using one affect the demand for the other? Finally, think about the relationship between electric vehicles and the equipment needed to run them.
To evaluate this view, you need to consider both the strengths and weaknesses of a gasoline tax. Explain how it is intended to work using the concept of negative externalities. Then, critically assess its effectiveness. Crucially, the question asks if it is the 'most effective' way, so you must compare it with alternative policies designed to achieve the same goal.
Question 4
HardPaper 1 · no calculator25 marksExplain how one determinant of demand might lead to an increase in the price of electric vehicles and how one determinant of supply might lead to a decrease in the price of electric vehicles.
Using real-world examples, evaluate the proposition that governments should always use price ceilings (maximum prices) to make essential goods more affordable.
For the first part, think about factors that would make more people want to buy electric vehicles at any given price. For the second part, consider factors that would make it cheaper or easier for firms to produce electric vehicles. Use separate demand and supply diagrams to illustrate each change and its effect on the equilibrium price.
Start by explaining how a price ceiling works using a diagram. Then, consider the arguments for this policy (e.g., equity, affordability) and the arguments against it (e.g., shortages, black markets). Use a specific real-world example, like rent control or food price caps, to support your evaluation. The word 'always' is a key part of the proposition to evaluate.
Question 5
HardPaper 1 · no calculator25 marks(a) Explain why a firm in perfect competition is considered to be both productively and allocatively efficient in the long run, whereas a monopoly is not.
(b) Using real-world examples, evaluate the effectiveness of government intervention aimed at reducing the market power of monopolies.
Start by defining productive efficiency (producing at minimum average total cost) and allocative efficiency (producing where price equals marginal cost). Then, for each market structure (perfect competition and monopoly), draw the long-run equilibrium diagram and use it to explain whether these two types of efficiency are achieved.
Consider the reasons why governments intervene to control monopolies (e.g., to correct allocative inefficiency). Then discuss different types of intervention, such as price regulation, competition policy (anti-trust laws), and nationalization. For each type, evaluate its strengths and weaknesses, supporting your points with specific real-world examples of government actions against firms like Google, Microsoft, or utility companies.
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Where marks are lost
- No real-world example, or a stated one. An answer that names a country and stops cannot reach the top two bands.
- One-sided argument. Balance is an explicit axis. A student who argues only that a policy works is capped at 9 out of 15 on that axis alone.
- Diagram present but not explained. The diagram bullet escalates across three bands: included, included and explained, included and fully explained. A diagram dropped into an answer without prose that refers to it sits at 5 to 6 on a 10-mark part.
