Microeconomics Exam Study Guide: Market Equilibrium, Surplus, Externalities, Costs, and Perfect Competition

Market Equilibrium and Surplus

Consumer and Producer Surplus

Consumer surplus and producer surplus are key concepts in microeconomics that measure the benefits to buyers and sellers in a market.

• Consumer Surplus: The difference between what a consumer is willing to pay for a good and what they actually pay.

• Producer Surplus: The difference between the price a producer receives for a good and the minimum price they are willing to accept.

• Example: If Frieda is willing to pay $75 for roses but buys them for $75, her consumer surplus is $0. If Lucinda buys a GPS for $250 but values it at $325, her consumer surplus is $75.

Formula for Surplus:

• Consumer Surplus: $CS = WTP - P$

• Producer Surplus: $PS = P - MC$ (where MC is marginal cost)

Market Equilibrium

Market equilibrium occurs where the quantity demanded equals the quantity supplied at a certain price.

• Equilibrium Price: The price at which supply and demand intersect.

• Equilibrium Quantity: The quantity bought and sold at the equilibrium price.

• Surplus and Shortage: If price is above equilibrium, there is a surplus; if below, a shortage.

Economic Efficiency

Economic efficiency is achieved when the sum of consumer and producer surplus is maximized.

• Efficient Market Outcome: Occurs at equilibrium where marginal benefit equals marginal cost.

• Deadweight Loss: Loss of total surplus due to market inefficiency, such as price controls or taxes.

Price Controls and Market Intervention

Price Ceilings

A price ceiling is a government-imposed limit on how high a price can be charged for a product.

• Binding Price Ceiling: Set below equilibrium price, causing a shortage.

• Example: If the rent ceiling is $1,000 and equilibrium rent is higher, quantity supplied is less than quantity demanded, leading to a shortage of apartments.

Surplus After Price Controls

• Consumer Surplus: May increase or decrease depending on the price control.

• Producer Surplus: Usually decreases with a binding price ceiling.

Externalities and Public Goods

Externalities

An externality is a cost or benefit that affects a third party not directly involved in a transaction.

• Positive Externality: Benefits others (e.g., vaccination).

• Negative Externality: Imposes costs on others (e.g., pollution).

• Marginal Social Benefit (MSB): The total benefit to society from consuming one more unit, including private and external benefits.

• Marginal Social Cost (MSC): The total cost to society from producing one more unit, including private and external costs.

Correcting Externalities:

• Government can use taxes, subsidies, or regulations to internalize externalities.

• Pigovian Subsidy: A subsidy equal to the external benefit to encourage positive externalities.

• Formula for Pigovian Subsidy: $Subsidy = P_E - P_C$ (where $P_E$ is price with externality, $P_C$ is competitive price)

Public Goods and Common Resources

• Public Goods: Non-excludable and non-rivalrous (e.g., national defense).

• Common Resources: Non-excludable but rivalrous (e.g., fisheries).

• Free Rider Problem: People benefit from a good without paying for it.

Production and Costs

Marginal Product and Marginal Cost

Marginal product is the additional output produced by one more unit of input. Marginal cost is the additional cost of producing one more unit of output.

• Marginal Product (MP): $MP = \frac{\Delta Q}{\Delta L}$

• Marginal Cost (MC): $MC = \frac{\Delta TC}{\Delta Q}$

• Example: If the 5th worker increases output from 50 to 56 pounds, $MP = 6$ pounds.

Fixed and Variable Costs

• Fixed Costs (FC): Costs that do not change with output (e.g., rent).

• Variable Costs (VC): Costs that change with output (e.g., labor, materials).

• Total Cost (TC): $TC = FC + VC$

• Average Fixed Cost (AFC): $AFC = \frac{FC}{Q}$

• Average Variable Cost (AVC): $AVC = \frac{VC}{Q}$

• Average Total Cost (ATC): $ATC = \frac{TC}{Q}$

Cost Curves

• Marginal Cost Curve: Typically U-shaped due to increasing and then decreasing returns.

• Average Total Cost Curve: Also U-shaped, reflecting spreading of fixed costs and variable costs.

• Average Variable Cost Curve: Lies below ATC and approaches it as output increases.

• Example Table:

Number of Workers	Mushrooms per Day (pounds)
1	12
2	33
3	43
4	50
5	56

Additional info: This table illustrates marginal product calculation for labor input.

Perfect Competition and Firm Behavior

Profit Maximization

Firms in perfect competition maximize profit where marginal cost equals marginal revenue.

• Profit-Maximizing Output: $MC = MR$

• Short-Run Supply Curve: The portion of the marginal cost curve above average variable cost.

• Loss-Minimizing Output: If price is below ATC but above AVC, the firm minimizes losses by producing where $MC = MR$.

Entry and Exit in Perfect Competition

• Entry: If firms earn economic profit, new firms enter, increasing supply and lowering price.

• Exit: If firms incur losses, some exit, decreasing supply and raising price.

• Long-Run Equilibrium: Firms earn zero economic profit; $P = ATC$.

Demand Curve for Individual Firm

• Perfectly Elastic: The demand curve for an individual firm in perfect competition is horizontal at the market price.

Implicit and Explicit Costs

Definitions

• Explicit Costs: Direct, out-of-pocket payments (e.g., wages, rent).

• Implicit Costs: Opportunity costs of using resources owned by the firm (e.g., foregone salary).

• Accounting Profit: $Accounting\ Profit = Total\ Revenue - Explicit\ Costs$

• Economic Profit: $Economic\ Profit = Total\ Revenue - (Explicit\ Costs + Implicit\ Costs)$

Summary Table: Key Cost Concepts

Term	Definition
Fixed Cost (FC)	Cost that does not vary with output
Variable Cost (VC)	Cost that varies with output
Total Cost (TC)	Sum of fixed and variable costs
Average Fixed Cost (AFC)	FC divided by output
Average Variable Cost (AVC)	VC divided by output
Average Total Cost (ATC)	TC divided by output
Marginal Cost (MC)	Change in TC divided by change in output

Graphical Analysis

Interpreting Cost and Supply Curves

• Cost curves (MC, ATC, AVC) are used to determine profit-maximizing output and loss-minimizing output.

• Supply and demand diagrams illustrate market equilibrium, surplus, and effects of interventions.

Applications and Examples

• Tax Incidence: The burden of a tax is shared between buyers and sellers depending on elasticity.

• External Benefits: Vaccination provides benefits beyond the individual, justifying subsidies.

• Common Resources: Overuse can lead to depletion, requiring regulation or property rights.

Additional info: These notes synthesize the main topics covered in the exam questions, including market equilibrium, surplus, externalities, cost structures, and perfect competition, with definitions, formulas, and examples for comprehensive review.