302 PART • Producers, Consumers, and Competitive Markets for example, that the firm uses labor and capital inputs; its capital equipment has been purchased Accounting profit will equal revenues R minus labor cost wL, which is positive Economic profit p, however, equals revenues R minus labor cost wL minus the capital cost, rK: p = R - wL - rK As we explained in Chapter 7, the correct measure of capital cost is the user cost of capital, which is the annual return that the firm could earn by investing its money elsewhere instead of purchasing capital, plus the annual depreciation on the capital • zero economic profit A firm is earning a normal return on its investment—i.e., it is doing as well as it could by investing its money elsewhere ZERO ECONOMIC PROFIT When a firm goes into a business, it does so in the expectation that it will earn a return on its investment A zero economic profit means that the firm is earning a normal—i.e., competitive—return on that investment This normal return, which is part of the user cost of capital, is the firm’s opportunity cost of using its money to buy capital rather than investing it elsewhere Thus, a firm earning zero economic profit is doing as well by investing its money in capital as it could by investing elsewhere—it is earning a competitive return on its money Such a firm, therefore, is performing adequately and should stay in business (A firm earning a negative economic profit, however, should consider going out of business if it does not expect to improve its financial picture.) As we will see, in competitive markets economic profit becomes zero in the long run Zero economic profit signifies not that firms are performing poorly, but rather that the industry is competitive ENTRY AND EXIT Figure 8.13 shows how a $40 price induces a firm to increase output and realize a positive profit Because profit is calculated after subtracting the opportunity cost of capital, a positive profit means an unusually high return on a financial investment, which can be earned by entering a profitable industry This high return causes investors to direct resources away from other industries and into this one—there will be entry into the market Eventually the increased production associated with new entry causes the market supply curve to shift to the right As a result, market output increases and the market price of the product falls.7 Figure 8.14 illustrates this In part (b) of the figure, the supply curve has shifted from S1 to S2, causing the price to fall from P1 ($40) to P2 ($30) In part (a), which applies to a single firm, the long-run average cost curve is tangent to the horizontal price line at output q2 A similar story would apply to exit Suppose that each firm’s minimum longrun average cost remains $30 but the market price falls to $20 Recall our discussion earlier in the chapter; absent expectations of a price change, the firm will leave the industry when it cannot cover all of its costs, i.e., when price is less than average variable cost But the story does not end here The exit of some firms from the market will decrease production, which will cause the market supply curve to shift to the left Market output will decrease and the price of the product will rise until an equilibrium is reached at a break-even price of $30 To summarize: In a market with entry and exit, a firm enters when it can earn a positive longrun profit and exits when it faces the prospect of a long-run loss We discuss why the long-run supply curve might be upward sloping in the next section