8 | Perfect Competition • Perfect Competition and Why It Matters • How Perfectly Competitive Firms Make Output Decisions • Entry and Exit Decisions in the Long Run • Efficiency in Perfectly Competitive Markets

What are the Conditions of Perfect Competition? Firms are said to be in perfect competition when the following conditions occur: many firms produce identical products; many buyers are available to buy the product, and many sellers are available to sell the product; sellers and buyers have all relevant information to make rational decisions about the product being bought and sold; and firms can enter and leave the market without any restrictions—in other words, there is free entry and exit into and out of the market.

In the short run, the perfectly competitive firm will seek the quantity of output where profits are highest or, if profits are not possible, where losses are lowest. In this example, the “short run” refers to a situation in which firms are producing with one fixed input and incur fixed costs of production. (In the real world, firms can have many fixed inputs.) In the long run, perfectly competitive firms will react to high profits by increasing production. They will respond to continued losses by reducing production or exiting the market. Ultimately, a long-run equilibrium will be attained when no new firms want to enter the market and existing firms do not want to leave the market, as economic profits (above normal profits) have been driven down to zero.

A Model of a Competitive Firm A perfectly competitive firm has only one major decision to make — namely, what quantity to produce. To understand why this is so, consider a different way of writing out the basic definition of profit: Profit = Total revenue − Total cost = (Price)(Quantity produced) − (Average cost)(Quantity produced)

TC TC

Note that Total Revenue = P*Q and this is a straight line in the graph on the right Note also that Maximum Profit occurs where the slope of TC and TR are equal. This is why we say that profit maximum output occurs where MR = MC In fact, we can write P = MR = MC

The graphs to the left show clearly how to derive the Average and Marginal Cost curves from the Total Cost curve.

Profit, Loss, Shutdown The marginal cost curve can be divided into three zones, based on where it is crossed by the average cost and average variable cost curves. The point where MC crosses AC is called the zero profit point. If the firm is operating at a level of output where the market price is at a level higher than the zero-profit point, then price will be greater than average cost and the firm is earning profits. If the price is exactly at the zero profit point, then the firm is making zero profits. If price falls in the zone between the shutdown point and the zero profit point, then the firm is making losses but will continue to operate in the short run, since it is covering its variable costs. However, if price falls below the price at the shutdown point, then the firm will shut down immediately, since it is not even covering its variable costs.