Market Structure: Perfect Competition
Market structure describes the competitive environment. Perfect competition is the most competitive structure — the benchmark against which all others are compared.
Characteristics
Many buyers and sellers — none can influence price. Homogeneous product — identical goods. Free entry and exit — no barriers. Perfect information — all know prices and quality. Price takers — firms accept market price. Examples (approximately): agricultural commodities, stock markets.
Revenue
Since firms are price takers: P = AR = MR. Demand curve facing individual firm is perfectly elastic (horizontal) at market price. TR = P × Q (straight line).
Profit Maximisation
All firms maximise profit where MR = MC (MC rising, P > AVC). Since MR = P: the condition becomes P = MC. If P > MC, produce more. If P < MC, produce less. MC curve above AVC is the firm’s supply curve.
Short-Run Equilibrium
Supernormal profit: P > ATC (profit = (P−ATC)×Q). Normal profit: P = ATC. Losses: P < ATC. Continue if P > AVC (covering variable costs). Shut down if P < AVC.
Long-Run Equilibrium
Free entry/exit eliminates supernormal profits and losses. Firms enter when profits exist (increasing supply, lowering price). Firms exit when losses occur (decreasing supply, raising price). Long-run: P = MR = MC = ATC (minimum). Achieves allocative efficiency (P = MC) and productive efficiency (minimum ATC).
Industry Supply
Short-run: horizontal sum of firms’ MC curves. Long-run: depends on costs — constant-cost (horizontal), increasing-cost (upward), decreasing-cost (downward). Most industries are increasing-cost.
Summary
Perfect competition achieves allocative and productive efficiency in long run. Profit maximisation at P = MC, short-run profit/loss analysis, and long-run entry/exit adjustment are foundational concepts.
Short-Run Profit/Loss Scenarios
| Scenario | Condition | Decision | Profit/Loss |
|---|---|---|---|
| Supernormal Profit | P > ATC | Produce at MR=MC | Profit = (P − ATC) × Q |
| Normal Profit | P = ATC | Produce (break-even) | Zero economic profit |
| Loss but Continue | AVC < P < ATC | Continue — covers variable costs + part of fixed | Loss < TFC |
| Shut Down | P < AVC | Stop production | Loss = TFC only |
Key insight: Shutdown point = P = minimum AVC (NOT ATC). A firm making losses should still produce if P > AVC because revenue covers variable costs and contributes toward fixed costs.
Worked Example: Profit Maximisation
Market price P = Rs 50. Cost data:
| Q | TC | MC | ATC | TR (P×Q) | Profit |
|---|---|---|---|---|---|
| 0 | 100 | — | — | 0 | −100 |
| 1 | 130 | 30 | 130 | 50 | −80 |
| 2 | 150 | 20 | 75 | 100 | −50 |
| 3 | 160 | 10 | 53 | 150 | −10 |
| 4 | 180 | 20 | 45 | 200 | +20 |
| 5 | 220 | 40 | 44 | 250 | +30 (MAX) |
| 6 | 280 | 60 | 47 | 300 | +20 |
Profit maximised at Q = 5 where MC (40) is closest to P (50) without exceeding it, and MC is rising. Profit = 250 − 220 = Rs 30.
Long-Run Adjustment Process
| If Short-Run Has... | Then... | Effect on Market | Until... |
|---|---|---|---|
| Supernormal profit | New firms ENTER (attracted by profits) | Supply increases → price falls | Only normal profit remains |
| Losses | Some firms EXIT (can’t sustain losses) | Supply decreases → price rises | Remaining firms earn normal profit |
Long-run equilibrium: P = MR = MC = ATC (minimum). Both allocative efficiency (P = MC — right amount produced) and productive efficiency (minimum ATC — lowest possible cost) achieved. This is why perfect competition is the efficiency benchmark.
Exam Tips
Tip 1: The 4 profit/loss scenarios table is the MOST tested topic — memorise conditions and decisions. Tip 2: Shutdown point = P < AVC (NOT P < ATC) — common exam trap. Tip 3: Long-run equilibrium condition P = MR = MC = min ATC must be stated precisely. Tip 4: In numerical problems, find Q where MC ≤ P with MC rising.