Why is the marginal revenue MR curve horizontal at the current market price for a perfectly competitive firm?

Pure or perfect competition is rare in the real world, but the model is important because it helps analyze industries with characteristics similar to pure competition. This model provides a context in which to apply revenue and cost concepts developed in the previous lecture. Examples of this model are stock market and agricultural industries.

1. Many sellers: there are enough so that a single seller’s decision has no impact on market price.

2. Homogenous or standardized products: each seller’s product is identical to its competitors’.

3. Firms are price takers: individual firms must accept the market price and can exert no influence on price.

4. Free entry and exit: no significant barriers prevent firms from entering or leaving the industry.

The individual firm will view its demand as perfectly elastic. A perfectly elastic demand curve is a horizontal line at the price. The demand curve for the industry is not perfectly elastic, it only appears that way to the individual firms, since they must take the market price no matter what quantity they produce. Therefore, the firm’s demand curve is a horizontal line at the market price.

Marginal revenue (MR) is the increase in total revenue resulting from a one-unit increase in output. Since the price is constant in the perfect competition. The increase in total revenue from producing 1 extra unit will equal to the price. Therefore, P= MR in perfect competition.

Short Run Analysis

In the short run, the firm has fixed resources and maximizes profit or minimizes loss by adjusting output. Firms should produce if the difference between total revenue and total cost is profitable (EP >0), or if the loss is less than the fixed cost (EP> - FC). The firm should not produce, but should shut down in the short run if its loss exceeds its fixed costs. By shutting down, its loss will just equal those fixed costs. Fixed cost in real life would be rent of the office, business license fees, equipment lease, etc. These cost would have to be paid with or without any output. Therefore, fixed cost would be the loss of shut down at any time. If by producing one unit of output, this loss could be lowered, then this unit should be produced to minimize the loss. However, if by producing one unit of output, this loss would be higher , then this unit should not be produced. The firm should shut down, just pay for the fixed cost.

If EP< - FC  firm should shut down. Then its lost will be the Fixed cost. EP = - FC. In order for EP < - FC, market price, P, must be lower than the minimum AVC.

If EP>- FC, firm should produce. That is when market price is greater than minimum AVC.

Marginal revenue and marginal cost (MC) are compared to decide the profit-maximizing output.

If MR > MC, then the firm should continue to produce.

If MR = MC, then the firm should stop producing the additional unit. As the additional unit’s MC would be higher according to law of diminishing returns, MR would be less than MC; that is, the firm would loss profit by producing additional units. Therefore, this is the profit maximizing output level.

If MR < MC, then the firm should lower its output.

In conclusion:

The shutdown point is the level of output and price at which the firm just covers its total variable cost. If the MR of the product is less than the minimum average variable cost (min AVC), the firm will shut down because this action minimizes the firm’s loss. In this case, the firm’s economic loss equals its total fixed costs. If MR < min AVC, then each additional unit produced would increase the loss. For pure competition, MR is equal to price as the firm is facing a perfectly elastic demand. Therefore, for short run, if Price < min AVC, then the firm should shut down. If Price > min AVC, then the firm should produce. Price and MC are compared to find the profit maximizing or loss minimizing output level. The supply curve of the pure competition firms would be the portion of the MC curve above the min AVC.

1. If EP < - FC or Market P < Min AVC, firm should shut down. Output = 0 , and EP = -FC

2. If EP > - FC or Market P > Min AVC, firm should produce. Firm's output level should be at where MR=MC or P=MC.  Use EP = TR - TC to get economic profit of the firm.

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Four Market Structures

The focus of this lecture is the four market structures. Students will learn the characteristics of pure competition, pure monopoly, monopolistic competition, and oligopoly. Using the cost schedule from the previous lecture, the idea of profit maximization is explored.

OBJECTIVES

1. Identify various market structures and their characteristics.

2. Be able to category firms into four market structures.

3. Describe the effects of imperfect competition upon the market and the firm.

4. Understand the pricing structure of the four structures.

TOPICS

Please read all the lectures by clicking on the following topics.

PERFECT COMPETITION

PERFECT COMPETITION CONT.

PERFECT COMPETITION EXAMPLE

PURE MONOPOLY

MONOPOLY EXAMPLE

PRICE DISCRIMINATION

MONOPOLISTIC COMPETITION

OLIGOPOLY

TECHNOLOGICAL DEVELOPMENT

ECONOMIC EFFICIENCY

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The average revenue curve for a perfectly competitive firm is horizontal due to the fact that it faces perfectly elastic demand at the market determined price. This is because there is a significant amount of buyers and sellers in the market alongside perfect information meaning that if a firm was to raise its price, customers in the market would move to a different producer and purchase the good at the original price and the firm raising their price would receive no revenue. Marginal revenue is also horizontal because the increase in revenue from producing one more unit of output is equal to the price of the good meaning it remains constant, thus horizontal. 

On the other hand a monopoly firm, due to it being the only producer, is the industry. due to the industry facing a downward sloping demand curve so does the monopoly firm. This means that it can only increase sales by reducing price or increase price by reducing output. Therefore they are price makers or quantity setters. The demand curve shows the quantity demanded at any price e.g. a water company might sell 2 billion gallons of water at 1p per gallon. The price per gallon is equal to the AR curve, therefore D=AR. If average revenue is falling then marginal revenue is falling, but at a faster rate and thus it is also downward sloping. 

Each firm in a perfectly competitive market is a price taker; the equilibrium price and industry output are determined by demand and supply. Figure 9.1 “The Market for Radishes” shows how demand and supply in the market for radishes, which we shall assume are produced under conditions of perfect competition, determine total output and price. The equilibrium price is $0.40 per pound; the equilibrium quantity is 10 million pounds per month.

Figure 9.1 The Market for Radishes. Price and output in a competitive market are determined by demand and supply. In the market for radishes, the equilibrium price is $0.40 per pound; 10 million pounds per month are produced and purchased at this price.

Because it is a price taker, each firm in the radish industry assumes it can sell all the radishes it wants at a price of $0.40 per pound. No matter how many or how few radishes it produces, the firm expects to sell them all at the market price.

The assumption that the firm expects to sell all the radishes it wants at the market price is crucial. If a firm did not expect to sell all of its radishes at the market price—if it had to lower the price to sell some quantities—the firm would not be a price taker. And price-taking behavior is central to the model of perfect competition.

Radish growers—and perfectly competitive firms in general—have no reason to charge a price lower than the market price. Because buyers have complete information and because we assume each firm’s product is identical to that of its rivals, firms are unable to charge a price higher than the market price. For perfectly competitive firms, the price is very much like the weather: they may complain about it, but in perfect competition there is nothing any of them can do about it.

This video explains how the market supply and demand curves determine the price of a good, and why firms in a perfectly competitive market are price takers.

Total Revenue

While a firm in a perfectly competitive market has no influence over its price, it does determine the output it will produce. In selecting the quantity of that output, one important consideration is the revenue the firm will gain by producing it.

A firm’s total revenue is found by multiplying its output by the price at which it sells that output. For a perfectly competitive firm, total revenue (TR) is the market price (P) times the quantity the firm produces (Q), or

TR = P x Q

The relationship between market price and the firm’s total revenue curve is a crucial one. Panel (a) of Figure 9.2 “Total Revenue, Marginal Revenue, and Average Revenue” shows total revenue curves for a radish grower at three possible market prices: $0.20, $0.40, and $0.60 per pound. Each total revenue curve is a linear, upward-sloping curve. At any price, the greater the quantity a perfectly competitive firm sells, the greater its total revenue. Notice that the greater the price, the steeper the total revenue curve is.

Figure 9.2 Total Revenue, Marginal Revenue, and Average Revenue. Panel (a) shows different total revenue curves for three possible market prices in perfect competition. A total revenue curve is a straight line coming out of the origin. The slope of a total revenue curve is MR; it equals the market price (P) and AR in perfect competition. Marginal revenue and average revenue are thus a single horizontal line at the market price, as shown in Panel (b). There is a different marginal revenue curve for each price.

Marginal Revenue, Price, and Demand for the Perfectly Competitive Firm

We have seen that a perfectly competitive firm’s marginal revenue curve is simply a horizontal line at the market price and that this same line is also the firm’s average revenue curve. For the perfectly competitive firm, MR=P=AR. The marginal revenue curve has another meaning as well. It is the demand curve facing a perfectly competitive firm.

Consider the case of a single radish producer, Tony Gortari. We assume that the radish market is perfectly competitive; Mr. Gortari runs a perfectly competitive firm. Suppose the market price of radishes is $0.40 per pound. How many pounds of radishes can Mr. Gortari sell at this price? The answer comes from our assumption that he is a price taker: He can sell any quantity he wishes at this price. How many pounds of radishes will he sell if he charges a price that exceeds the market price? None. His radishes are identical to those of every other firm in the market, and everyone in the market has complete information. That means the demand curve facing Mr. Gortari is a horizontal line at the market price as illustrated in Figure 9.3 “Price, Marginal Revenue, and Demand”. Notice that the curve is labeled d to distinguish it from the market demand curve, D, in Figure 9.1 “The Market for Radishes”. The horizontal line in Figure 9.3 “Price, Marginal Revenue, and Demand” is also Mr. Gortari’s marginal revenue curve, MR, and his average revenue curve, AR. It is also the market price, P.

Of course, Mr. Gortari could charge a price below the market price, but why would he? We assume he can sell all the radishes he wants at the market price; there would be no reason to charge a lower price. Mr. Gortari faces a demand curve that is a horizontal line at the market price. In our subsequent analysis, we shall refer to the horizontal line at the market price simply as marginal revenue. We should remember, however, that this same line gives us the market price, average revenue, and the demand curve facing the firm.

Figure 9.3 Price, Marginal Revenue, and Demand. A perfectly competitive firm faces a horizontal demand curve at the market price. Here, radish grower Tony Gortari faces demand curve d at the market price of $0.40 per pound. He could sell q1 or q2—or any other quantity—at a price of $0.40 per pound.

More generally, we can say that any perfectly competitive firm faces a horizontal demand curve at the market price. We saw an example of a horizontal demand curve in the module on elasticity. Such a curve is perfectly elastic, meaning that any quantity is demanded at a given price.

Note that Figure 9.1 shows the market (and demand curve) for a perfectly competitive industry and Figure 9.3 shows the demand curve for a perfectly competitive firm.

This video demonstrates how average revenue equals marginal revenue, which equals price in a perfectly competitive market.

Self Check: Perfectly Competitive Firms and Industries

Answer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times.

You’ll have more success on the Self Check if you’ve completed the two Readings in this section.

Use this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.