曼昆经济学原理微观(全).ppt

* * Most students already know that monopoly means the firm is the only seller of its product. But the definition here has another very important part: In order for the firm to be considered a monopoly, the product it sells must have no close substitutes available from other firms. * * The horizontal axis of the graph measures number of homes provided electricity. The vertical axis measures the average total cost of providing electricity per home. * * A competitive firm is a price-taker, can sell as much as it wants at the market price. In effect, the competitive firm sells a product for which there are many perfect substitutes, so demand for its product is perfectly elastic; if it raises its price above the market price, demand for its product falls to zero. The relationship between P and MR is what distinguishes a competitive firm from a monopoly firm, in terms of both firm behavior and welfare implications. * * This slide introduces the notion that MR is not equal to P for the monopolist. The next slide presents an exercise to lead students to see for themselves what this relationship looks like. * When the AR column appears, note that AR = P at every quantity. This, of course, is a tautology. When the MR column appears, note that MR is less than P. This is not as easy to see, because the MR numbers are offset from the rows of the table, just as if you were in an elevator stuck between two floors. But students can still see that MR P. For example, in the range of output of Q=2 to Q=3, the price ranges from $3.50 to $3.00, but MR is only $2. * * The numbers in the table are from the preceding exercise. Students can see either from the table or the graph that, at any Q, MR P. * * Note that a competitive firm has the output effect but not the price effect: the competitive firm does not need to reduce its price in order to sell a larger quantity, so, for the competitive firm, MR = P. * * Most students quickly grasp the following ex