Questions: Perfect Competition: Firm Behavior and Industry Equilibrium

Question 1

A competitive industry is in long-run equilibrium. A consultant reports 'all firms in this industry earn zero profit.' An economist's correct interpretation is:

• A. The industry is in crisis — firms are on the verge of bankruptcy
• B. Firms are earning exactly the competitive return on capital — what they could earn elsewhere
• C. Firms have no revenue because prices have been driven to zero
• D. The industry is characterized by natural monopoly and should be regulated

Answer: (B)

Zero economic profit means firms earn exactly the opportunity cost of capital — no more, no less. This is the normal competitive return, not a sign of crisis. Accountants would record these same firms as profitable (positive accounting profit), because accounting profit doesn't subtract the opportunity cost of capital. The economist's 'zero profit' means 'no economic rent above the competitive return.' This is the long-run equilibrium benchmark of a well-functioning competitive market.

Question 2

A profitable new firm enters a perfectly competitive industry. The long-run effect on the market price is:

• A. Price rises as existing firms raise prices to protect margins
• B. Price falls as entry increases industry supply, until economic profit = 0 for all firms
• C. Nothing — a price-taker firm cannot affect the market price regardless of entry
• D. Price is indeterminate because each firm sets its own price

Answer: (B)

Positive economic profit signals that capital is earning above its opportunity cost, attracting new entrants. Each new firm adds to market supply, shifting the supply curve rightward and pushing the market price down. The process continues until price falls to minimum ATC, at which point economic profit = 0 and the incentive for further entry disappears. Each individual firm is a price-taker, but collective entry affects the market supply curve and thereby the equilibrium price.

Question 3

In a perfectly competitive market, a firm that shuts down in the short run earns zero profit.

• T. True
• F. False

Answer: False

A firm that shuts down in the short run still owes its fixed costs — rent, equipment leases, contractual obligations — which it cannot escape in the short run. Its profit is negative: it earns zero revenue but loses its total fixed costs. The shutdown decision compares this certain loss (fixed costs) against the loss from operating. A firm operates as long as P > AVC, because earning some contribution above variable costs reduces the fixed-cost loss. The floor from shutdown is negative fixed costs, not zero.

Question 4

Long-run equilibrium in perfect competition occurs at the minimum of the average total cost curve because that is the only point where P = MC = ATC simultaneously.

• T. True
• F. False

Answer: True

Correct. Three conditions must hold simultaneously in long-run equilibrium: (1) P = MC (profit maximization); (2) P = ATC (zero economic profit); (3) P = MR (price-taking). These can only hold at the point where MC crosses ATC at its minimum — because MC = ATC only at the minimum of ATC (when MC is below ATC, ATC is falling; when MC is above ATC, ATC is rising). Long-run equilibrium requires operating at exactly that point.

Question 5

Why does zero economic profit in long-run competitive equilibrium not mean that successful firms in the industry are doing something wrong or should exit?

Model answer: Economic profit is measured after subtracting the opportunity cost of all resources, including capital. A firm earning 'zero economic profit' is earning exactly what its capital could earn in the next best investment — the market rate of return. Owners have no incentive to exit because they are not doing worse than they would elsewhere. Accountants measure profit differently and don't subtract opportunity costs, so the same firm shows positive accounting profit. Zero economic profit is the efficiency benchmark, not a sign of failure.

This distinction is one of the most important in microeconomics. 'Normal profit' is what accountants call profit; 'zero economic profit' is what economists call the same thing, once opportunity costs are properly accounted for. Economic profit above zero is an efficiency signal: it means a sector is earning above the competitive return, so more capital should flow there. Economic profit below zero is the exit signal. Long-run equilibrium at zero economic profit means the sector is neither over- nor under-supplied.