Professor Christina Romer LECTURE 7 COMPETITIVE FIRMS IN THE LONG RUN FEBRUARY 6, 2018

Transcription

1 Economics 2 Spring 2018 rofessor Christina Romer rofessor David Romer LECTURE 7 COMETITIVE FIRMS IN THE LONG RUN FEBRUARY 6, 2018 I. A LITTLE MORE ON SHORT-RUN ROFIT-MAXIMIZATION A. The condition for short-run profit-maximization B. The industry marginal cost curve C. The two-way interaction between individual firms and the market II. AVERAGE TOTAL COST AND SHORT-RUN ROFITS A. Average total cost (atc) B. Graphing atc C. atc, price, and profits D. Three possible profit scenarios III. LONG-RUN ROFIT MAXIMIZATION A. Short-run profits as a signal for entry or exit B. The impact of entry or exit on the industry supply curve C. Long-run equilibrium D. Example: A fall in demand 1. The immediate effect of the fall in demand 2. rofits and entry/exit 3. The new long-run equilibrium E. Example: A decrease in cost 1. The immediate effect of the fall in demand 2. rofits and entry/exit 3. The new long-run equilibrium IV. SOME IMLICATIONS OF LONG-RUN ROFIT-MAXIMIZATION A. The long-run industry supply curve B. Who enters or exits? C. A little on the case of heterogeneous long-run opportunity costs D. The invisible hand

2 Economics 2 Spring 2018 Christina Romer David Romer LECTURE 7 Competitive Firms in the Long Run February 6, 2018

3 Announcements roblem Set 2 is being handed out. It is due at the beginning of lecture next Tuesday (Feb. 13). The ground rules are the same as on roblem Set 1. Optional problem set work session: Thursday, 4:00 6:00, in 648 Evans. roblem Set 1 is being returned in section this week.

4 Announcements Journal article reading for Thursday (by Edward Glaeser and Erzo Luttmer): Read only the assigned pages. Don t stress over every word or parts you don t understand. Read for approach and findings; think about relevance for the consequences of not letting prices adjust.

5 I. A LITTLE MORE ON SHORT-RUN ROFIT-MAXIMIZATION

6 The rofit-maximizing Level of Output for a erfectly Competitive Firm mc mr (= MARKET ) q 1 q A competitive firm produces up to the point where = mc.

7 The Industry Supply Curve Is the Industry Marginal Cost Curve 1 S (= MC) Q 1 Q At a given, such as 1, each firm produces until where mc i =. The total amount produced is the point on the supply curve (Q 1 ). So: When the industry is producing Q 1, each firm s m.c. is 1. So: 1 is the marginal cost of producing 1 more unit when the industry is producing Q 1.

8 The Two-Way Interaction of Individual Firms and the Market Example: A Fall in an Input rice Market Individual Firm S 1 S 2 mc 1 mc mr 1 mr 2 Q 1 D 1 Q 2 Q q 2 q 1 q

9 II. AVERAGE TOTAL COST AND SHORT-RUN ROFITS

10 Recall: Average Total Cost Costs are measured as opportunity costs. Fixed costs: Costs that do not vary with how much is produced. Variable costs: Costs that do vary with how much is produced. Total cost: The sum of fixed and variable costs. Average Total Cost = Total Cost Quantity

11 Marginal Cost and Average Total Cost Cost (in $) mc atc The mc and atc curves cross at the lowest point of the atc curve. q

12 atc, rice, and rofits Recall: Now: rofits = Total Revenue Total Cost Total Revenue = q Total Cost = atc q So: rofits = ( q) (atc q) = ( atc) q So: rofits are positive, negative, or zero depending on whether atc is positive, negative, or zero.

13 Revenues, Costs, and rofits atc mc 1 e f atc 1 c d mr a b Revenues: Rectangle abef. Costs: abcd. rofits: cdef. q 1 q

14 Negative Economic rofits Market Individual Firm S atc mc atc 1 1 mr D Q q 1 q 1 < atc at q 1.

15 ositive Economic rofits Market Individual Firm S atc mc 1 mr atc 1 D Q 1 > atc at q 1. q 1 q

16 Zero Economic rofits Market Individual Firm S atc mc 1 atc 1 mr D Q 1 = atc at q 1. q 1 q

17 III. LONG-RUN ROFIT-MAXIMIZATION

18 The Signals Sent by rofits If there are negative profits: Some firms will reduce the scale of their operations, or exit. If there are positive profits: Some firms will expand the scale of their operations, or new firms will enter. Exit moves the industry supply curve to the left; entry moves it to the right. If there are zero profits: There are no forces tending to cause either contraction or expansion of the industry. In this situation, the industry is in long-run equilibrium.

19 Long-Run Equilibrium Market Individual Firm S atc mc 1 mr D Q q 1 q

20 Fall in Demand (Starting in Long-Run Equilibrium) Short-Run Effects Market Individual Firm S 1 atc 1 mc 1 1 mr 1 2 mr 2 D 2 D 1 Q 2 Q 1 Q q 2 q 1 q

21 Fall in Demand (Starting in Long-Run Equilibrium) Long-Run Effects Market Individual Firm S 3 S 1 atc 1 mc 1 1,3 mr 1,3 2 mr 2 D 2 D 1 Q 3 Q 2 Q 1 Q q 2 q 1,3 q

22 Fall in Marginal Cost (Starting in Long-Run Equilibrium) Short-Run Effects Market Individual Firm 1 2 S 1 S 2 mc atc 1 1 mc 2 atc 2 mr 1 mr 2 D Q 1 Q 2 Q q 1 q 2 q

23 Fall in Marginal Cost (Starting in Long-Run Equilibrium) Long-Run Effects Market Individual Firm D S 1 S 2 S 3 mc atc 1 1 mc 2 atc 2 mr 1 mr 2 mr 3 Q 1 Q 2 Q 3 Q q 1,3 q 2 q

24 IV. SOME IMLICATIONS OF LONG-RUN ROFIT MAXIMIZATION

25 The Long-Run Industry Supply Curve Market Individual Firm atc mc LR S Q The long-run industry supply curve is perfectly elastic at the minimum of atc. q 1 q

26 Other Implications of Long-Run rofit Maximization Who enters or exits? A little about what happens if there is variation in long-run opportunity cost. The invisible hand.