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🏭 Unit 3 · Production, Cost & Perfect Competition 🏠 Unit Hub 🗂 Flashcards 🗺 Cheat Sheet ⭐ Essentials 🎨 Visual Review 📝 MC Practice ✎ FRQ Practice

AP Microeconomics Unit 3 Essentials

The must-know terms and big ideas for Unit 3: Production, Cost, and the Perfect Competition Model. Every vocabulary word and concept you need to master.

← Back to Unit 3 hub
Big Idea 1
Diminishing returns shape every cost curve in the unit
As a firm adds more of a variable input to a fixed input, marginal product eventually falls. Because marginal cost is inversely related to marginal product, this single fact explains why the marginal cost curve is U-shaped — and why MC eventually rises and pulls up ATC and AVC behind it.
Production Diminishing Returns Cost Curves
Big Idea 2
MR = MC is the universal profit-maximizing rule
Whether a firm is a perfectly competitive price-taker or a monopolist with market power, it maximizes profit (or minimizes loss) at the quantity where marginal revenue equals marginal cost. What differs across market structures is how marginal revenue itself is determined — for a perfectly competitive firm, MR simply equals price.
Profit Maximization MR=MC Perfect Competition
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Production function
The relationship between the quantity of inputs a firm uses and the quantity of output it produces.
Production
Marginal product
The additional output produced by one more unit of a variable input, holding other inputs constant.
Production
Diminishing marginal returns
The principle that marginal product eventually decreases as more units of a variable input are added to a fixed input.
Production
Total fixed cost (TFC)
Costs that don't change with output level in the short run, such as rent.
Short-Run Costs
Total variable cost (TVC)
Costs that change with the level of output, such as materials and most labor.
Short-Run Costs
Total cost (TC)
The sum of total fixed and total variable cost: TC = TFC + TVC.
Short-Run Costs
Marginal cost (MC)
The additional cost of producing one more unit of output. Eventually rises due to diminishing marginal returns.
Short-Run Costs
Average total cost (ATC)
Total cost divided by quantity; equals AFC + AVC. Minimized where MC crosses it.
Short-Run Costs
Average variable cost (AVC)
Total variable cost divided by quantity. Minimized where MC crosses it.
Short-Run Costs
Average fixed cost (AFC)
Total fixed cost divided by quantity. Always falls as output rises since fixed cost is spread over more units.
Short-Run Costs
Economies of scale
Long-run average total cost falls as output increases, often due to specialization or bulk purchasing.
Long-Run Costs
Diseconomies of scale
Long-run average total cost rises as output increases, often due to coordination problems in very large firms.
Long-Run Costs
Explicit costs
Direct, out-of-pocket payments a firm makes for resources, such as wages and rent.
Profit
Implicit costs
The opportunity costs of using resources the firm already owns, such as foregone salary or rent.
Profit
Accounting profit
Total revenue minus explicit costs only.
Profit
Economic profit
Total revenue minus both explicit and implicit costs. Zero economic profit means a "normal profit" — covering all costs including opportunity cost.
Profit
Marginal revenue (MR)
The additional revenue from selling one more unit. For a perfectly competitive firm, MR = price.
Profit Maximization
MR = MC rule
The profit-maximizing (or loss-minimizing) condition: produce the quantity where marginal revenue equals marginal cost.
Profit Maximization
Price taker
A firm in perfect competition that has no influence over price and must accept the market price as given.
Perfect Competition
Shutdown point
Where price equals minimum average variable cost. Below this, the firm shuts down in the short run.
Perfect Competition
Break-even point
Where price equals minimum average total cost. At this price, economic profit is exactly zero.
Perfect Competition
Allocative efficiency
A condition where price equals marginal cost, so resources go to their highest-valued use.
Perfect Competition
Productive efficiency
A condition where a firm produces at the minimum point of its average total cost curve — the lowest possible per-unit cost.
Perfect Competition