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Market Structures

Short run and long run equilibrium in perfect competition

  • 3 things to know
  • All three components

Overview

Normal profit position for a firm in the short run, long run equilibrium for a firm in perfect competition and long run industry supply curve in a constant cost industry.

What you need to know

Answer each one before you reveal it.

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Key term

How does a perfectly competitive firm choose its output in the short run?

Key term

Describe short run equilibrium when a perfectly competitive firm earns abnormal profit.

Key term

Describe short run equilibrium when a perfectly competitive firm makes a loss.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How does a perfectly competitive firm choose its output in the short run?

    Model answer

    The firm produces where marginal cost equals the market price, since price equals marginal revenue. Marginal cost must be rising at that output.

  2. 2

    Describe short run equilibrium when a perfectly competitive firm earns abnormal profit.

    Model answer

    Average revenue lies above average cost at the profit maximising output. The gap multiplied by output is the abnormal profit earned in the short run.

  3. 3

    Describe short run equilibrium when a perfectly competitive firm makes a loss.

    Model answer

    Average cost lies above the market price at the profit maximising output. The firm minimises its loss and stays open while price covers average variable cost.

  4. 4

    What is the normal profit position for a firm in the short run?

    Model answer

    A firm earns normal profit when the market price just equals average total cost. The firm covers all its costs, including the return needed to stay in the industry.

  5. 5

    How does the short run adjust to the long run when firms earn abnormal profit?

    Model answer

    Abnormal profit attracts new firms into the industry, which shifts industry supply to the right. The market price falls until each firm earns only normal profit.

  6. 6

    How does the short run adjust to the long run when firms make losses?

    Model answer

    Losses drive firms out of the industry, which shifts industry supply to the left. The market price rises until the remaining firms earn normal profit.

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