Perfect Competition

Specification Coverage: Edexcel unit 3.4.2 - Perfect Competition. Students should be able to identify the key characteristics of perfect competition, explain why firms are price takers, analyse short-run profit and loss positions, explain the adjustment process to long-run equilibrium, and apply efficiency conditions in the long run.

Key Characteristics

  • Many buyers and sellers: Each firm is infinitely small with negligible market power.
  • Homogeneous products: All firms sell identical products, so consumers have no preference for one firm over another.
  • Perfect information: Buyers and sellers have full knowledge of prices and products in the market.
  • Freedom of entry and exit: Firms can enter or leave the market without restrictions or cost, allowing for long-run adjustments.

These characteristics ensure that firms in perfect competition are price takers, meaning they accept the market price as given and cannot influence it through their own actions.

The Firm's Demand Curve

Because firms in perfect competition are price takers, the demand curve facing an individual firm is perfectly elastic, so it is horizontal.

This means \( P = MR = AR \).

The market price itself is determined by market supply and demand.

Two panels showing industry supply and demand setting the price the individual perfectly competitive firm must accept
Figure 1: The market price in perfect competition is determined by industry supply and demand. The firm's demand curve is perfectly elastic at this price.

Short-Run Equilibrium: Profit and Loss

The firm maximises profit where \( MC = MR \).

Short run, Supernormal Profit

Perfect competition firm earning short-run supernormal profit, shaded where average revenue is above average cost
Figure 2: In the short run, a firm in perfect competition can earn supernormal profit if the price is above the average cost. The shaded area represents supernormal profit.

Short run, Loss

Perfect competition firm making a short-run loss, shaded where average cost is above average revenue
Figure 3: In the short run, a firm in perfect competition can incur a loss if the price is below the average cost. The shaded area represents the loss.

Long-Run Equilibrium: Normal Profit Only

Because there is freedom of entry and exit, perfect competition moves to a long-run equilibrium where firms earn only normal profit, so \( AR = AC \).

From Short-Run Supernormal Profit to Long-Run Equilibrium

  • In the short run, firms may make supernormal profit.
  • These profits attract new firms into the industry.
  • Industry supply increases and shifts to the right.
  • The market price falls.
  • The firm's horizontal demand curve falls until it becomes tangent to the minimum point of the AC curve.
  • At this point, \( P = AR = AC = MC \) and firms earn normal profit.
Perfect competition diagram showing entry competing supernormal profit away until only normal profit remains
Figure 4: The adjustment process from short-run supernormal profit to long-run equilibrium in perfect competition. The firm's demand curve shifts down as new firms enter, eliminating supernormal profit and reaching the long-run equilibrium where \( P = AR = AC = MC \).

From Short-Run Loss to Long-Run Equilibrium

  • In the short run, firms may make losses.
  • Some firms leave the industry.
  • Industry supply decreases and shifts to the left.
  • The market price rises.
  • The firms' horizontal demand curves rise until they become tangent to the minimum point of the AC curve.
  • At this point, \( P = AR = AC = MC \) and firms earn normal profit.
Perfect competition diagram showing firms leaving until losses are removed and normal profit is restored
Figure 5: The adjustment process from short-run loss to long-run equilibrium in perfect competition. The firm's demand curve shifts up as firms exit, eliminating losses and reaching the long-run equilibrium where \( P = AR = AC = MC \).

Efficiency in Long-Run Equilibrium

Productive efficiency: Yes - Firms in perfect competition produce at the minimum point of the average cost curve, where \( AC = MC \).

Allocative efficiency: Yes - Firms in perfect competition produce where \( MC = AR \), ensuring that resources are allocated efficiently.

Dynamic efficiency: No - Firms in perfect competition earn only normal profit in the long run, which may limit their ability to invest in research and development.

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Seven original multiple-choice questions on the conditions for perfect competition, the firm as a price taker, and the adjustment to long-run equilibrium.

Practice Questions: 3.4.2 Perfect Competition