1. Part 6 Perfect Competition
Many markets are characterized by competitive conditions
Theory of competitive markets is based on a model of “perfect competition” – an idealized competitive market
- Many buyers and sellers
- Identical outputs
- Free entry and exit
- Complete information

2. The Firm Under Perfect Competition
Firm must be small relative to the size of the market (minimum efficient scale must be small relative to the market)
Individual firms cannot affect the market price (price taker)
Price is set in the market as a whole, the individual firm adjusts output so as to maximize profit given the market price

3. The Firm’s Total Revenue and Marginal Revenue Curves
As the market price is given, the firm’s total revenue is its output times the market price (P x Q)
The TR function will be a straight line from the origin
The firm’s marginal revenue is MR = ΔTR/ΔQ
As all units of output sell for the same price
MR = P

4. The Firm’s TR and MR Curves
P = $1.25
125 Q
100 MR
MR = P
1.25 Q

5. Profit Maximization
The firm has to decide whether to produce at all, and if so what output to produce
The firm will produce in the short run so long as its variable costs can be covered
Assuming the firm produces at all, the profit maximizing output is where there is the maximum excess of TR over TC or where MR = MC

6. Profit Maximum: TR and TC$ TR
Economic Profit Q Q’ Q”
Profit Max
Profit Q Q’ Q* Q”
Loss
Profit/Loss

7. Profit Maximum: MR and MC$ MC P MR Q Q*
Why does MC = MR imply profit max?
What would happen to TR and TC if output
went up or down by a unit?

8. Profit in the Short Run MC $ MR P ATC Economic profit Q Q* $ MC
Normal profit
or break even
ATC P MR Q Q*

9. Economic Loss in the Short Run$ MC
ATC P MR Q* Q
Economic loss
Firm will produce Q* as long as P>AVC

10. Firm’s Short Run Supply Curve
The firm’s short run supply curve will be its MC curve above its AVC curve
If P is equal to or grater than Min AVC the firm will produce where P = MR = MC
If P < Min AVC the firm’s loss minimizing strategy is to shut down. Loss will equal TFC

11. Firm’s Short Run Supply Curve
Break even or
normal profit
point $
ATC MC
MR” P” P’
MR’ P MR
Shut down point
AVC Q Q’ Q” Q
At prices below P the firm will shut down
At prices between P and P’ the firm will
produce where MC=MR at an economic loss
At prices above P’ the firm will produce where
MC=MR at an economic profit

12. Market Supply Curve We can now derive the market supply curve
The supply curve of each firm is its MC curve above its min AVC point
The market supply curve is the horizontal sum of the supply curves of all the firms in the industry

13. Short Run Equilibrium of the Market and Firm
Market demand curve is the horizontal sum of all the demand curves of individuals
Short run market supply curve is the horizontal sum of all the short run supply curves of all the firms currently in the industry
Market price and quantity is determined by D = S
Each individual firm will produce at its profit max point of MR = MC

14. SR Equilibrium of Market and Firm
Market equilibrium P
S = ΣhMC P*
D = ΣhDi Q Q*
Equilibrium of the firm P MC MR P*
ATC q q*

15. Shifts in Demand in the Short Run
Shifts in demand will create a movement along the market short run supply curve, changing market price
Each individual firm will adjust output to its new profit max level as price changes, moving along its own short run supply curve

16. Long Run Adjustments In the long run capital is not fixed
Firms can change the size of their plants and move along their LAC curves
Firms can enter or leave the industry. They will enter if there is economic profit and leave if they are suffering economic losses
If firms change size or the number of firms in the industry changes the short run industry supply curve will shift
What conditions must hold for a perfectly competitive industry to be in long run equilibrium?

17. Long Run Equilibrium
Market price must adjust (via shifts in the short run supply curve) until all firms are just making normal profit
With normal profit there is no economic profit to attract new entrants and no economic losses to create exit
Also, for their to be no prospect of economic profit, price must equal minimum LAC
Otherwise firms could make economic profit by changing their plant size which would shift the SR supply curve of the industry

18. Long Run Equilibrium for Market and FirmP
S = ΣhSMC P*
D = ΣhDi Q Q*
ATC
SMC
LAC MR P* q*

19. Long Run Supply Curve P S S’ P’ LRS P D’ D Q Q Q’
D shifts to D’, raising market price to P’.
This will create excess profit for firms
attracting new entrants and shifting S to S’
where all economic profit is again eliminated
and new entry stops .
This diagram shows a constant cost industry.
Long run supply curve is horizontal

20. Possible Long Run Supply Curves
Constant cost industry -- horizontal LRS. Changes in the size of the industry do not affect firms’ costs of production
Increasing cost industry – upward sloping LRS. As an industry grows a factor price rises as a result, increasing costs for all firms
Decreasing cost industry – downward sloping LRS. As an industry grows a factor price falls as a result, decreasing costs for all firms—network effects
Technological change shifts the LRS

21. Are Competitive Markets Efficient?
In long run competitive equilibrium price is such that D=S and production is at min LAC
Productive efficiency—min LAC
The market D curve is can be interpreted as willingness to pay or marginal benefit curve
The market supply curve can be seen as the marginal opportunity cost of production curve
Competitive equilibrium is allocatively efficient (maximizes social surplus) provided all costs and benefits are reflected in the market D and S curves

22. Economic Inefficiencies
The efficient allocation may not be achieved even in competitive markets
Not all resources may be privately owned (open access resources)
It may not be possible for firms to capture peoples’ willingness to pay (public goods, external benefits)
Not all social costs may be reflected in the prices firms pay for factors of production (external costs)
Economic inefficiencies may also arise from lack of competition --Monopoly