What will you learn in this chapter?
• What the characteristics of a perfectly competitive market are.
• How to calculate average, marginal, and total revenue.
• How to find a firm’s optimal quantity of output.
• How to differentiate between a firm’s shut down and market exit decisions.
• How to analyze a firm’s short-run supply curve for a competitive market.
• How to analyze a firm’s long-run supply curve for a competitive
market, and what its implications are for profit-seeking firms.
• Why a long-run supply curve might slope upward.
• What the effect of a demand shift is on a market in long-run equilibrium.
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1© 2014 by McGraw-Hill Education 1
Chapter 13
Perfect Competition
© 2014 by McGraw-Hill Education 2
What will you learn in this chapter?
• What the characteristics of a perfectly competitive market are.
• How to calculate average, marginal, and total revenue.
• How to find a firm’s optimal quantity of output.
• How to differentiate between a firm’s shut down and market
exit decisions.
• How to analyze a firm’s short-run supply curve for a
competitive market.
• How to analyze a firm’s long-run supply curve for a competitive
market, and what its implications are for profit-seeking firms.
• Why a long-run supply curve might slope upward.
• What the effect of a demand shift is on a market in long-run
equilibrium.
© 2014 by McGraw-Hill Education 3
A competitive market
• This chapter analyzes how firms make
production decisions in a competitive
market.
• The characteristics of a competitive
market are:
– Full information exists.
– Buyers and sellers are price takers.
– The good or service is standardized.
– Firms freely enter and exit the market.
2© 2014 by McGraw-Hill Education 4
A competitive market
• Competitive markets have so much competition that no
one has the ability to affect market prices. Thus, all are
price takers.
• If a buyer or seller has the ability to noticeably affect
market prices, that person/firm has market power.
– The only seller of food on a plane can charge a very high price,
knowing that some people would be hungry enough to pay it.
– The only buyer of food at a market at the end of the day could
offer a very low price, knowing that some seller would be willing
to sell.
• Most sellers and buyers are not able to set their own
price, although they may have some ability to set prices.
• Participation in a competitive market places very specific
constraints on a firm’s ability to maximize profits.
© 2014 by McGraw-Hill Education 5
Revenues in a perfectly competitive market
In a perfectly competitive market, producers are able to sell
as much as they want without affecting the market price.
• Price does not change.
• Total revenue is price times quantity produced.
• Average revenue is total revenue divided by quantity.
• Marginal revenue is the change in revenue.
• Notice that P = MR = AR.
)5()4()3()2()1(
Quantity
of plantains
(bunches)
Price
(CFA Francs)
Total revenue Average revenue
(CFA Francs/bunch
of plantains)
Marginal revenue
(CFA Francs)
000,1000,1000,1000,11
000,1000,1000,2000,12
000,1000,1000,3000,13
000,1000,1000,4000,14
000,1000,1000,5000,15
(CFA Francs)
© 2014 by McGraw-Hill Education 6
Active Learning: Revenue of a firm in a
competitive market
Fill in the table for a price taking firm in a
competitive market.
Quantity Price
($)
Total revenue
($)
Average revenue
($)
Marginal revenue
($)
951
2
3
4
5
3© 2014 by McGraw-Hill Education 7
Profits and production decisions
• Firms seek to maximize profits.
• In a competitive market, the only choice that a
price-taking firm can make to affect profits is
the quantity of output to produce.
• The profit-maximizing quantity corresponds to
the quantity at which marginal revenue is
equal to the marginal cost.
© 2014 by McGraw-Hill Education 8
Profits and production decisions
Profit maximization occurs where MR = MC for a
perfectly competitive firm.
Quantity of
plantains
(bunches)
Total revenue
(CFA Francs)
Total cost Profit Marginalrevenue
(CFA Francs)
Marginal
cost
(CFA Francs)
Marginal
profit
(CFA Francs
1
2
3
4
5
• Profits are maximized at a quantity of 3 and 4.
• At a quantity of 4, MR =MC.
(CFA Francs) (CFA Francs)
1,000
2,000
3,000
4,000
5,000
1,200
1,800
2,600
3,600
4,800
-200
200
400
400
200
1,000
1,000
1,000
1,000
1,000
500
600
800
1,000
1,200
500
400
200
0
-200
© 2014 by McGraw-Hill Education 9
Profits and production decisions
• Point A: Produce more, as the
MR from the next unit is
greater than the MC.
• Point B: The profit-maximizing
quantity is at MR = MC (B).
• Point C: Producing at this
quantity causes a loss as the
MC is greater than the MR.
• Rule of thumb: Increase
production as long as MR >
MC, as total profit increases as
another unit is produced.
The profit maximizing point can be identified graphically.
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
1 2 3 4 5
MC
Plantains (bunches)
Price (CFA Francs)
Profit at point C is
lower than at point B,
because MC is higher
than MR.
B
A
C
MR
Profit at point A is lower than at point B because
marginal profit (marginal revenue -
positive. Marginal profit stays positive up to point B.
marginal cost) is
4© 2014 by McGraw-Hill Education 10
Deciding when to operate
Producing the quantity where MR = MC may not
always be to the firm’s advantage.
Quantity
of plantains Total revenue Total cost Profit
Marginal
revenue
Marginal
cost
Marginal
profit
1 800 1,200 -400 800 500 300
2 1,600 1,800 -200 800 600 200
-200 800 800 0
4 3,200 3,600 -400 800 1,000 -200
5 4,000 4,800 -800 800 1,200 -400
3 2,400 2,600
• Even though profit is maximized, it is negative.
– Optimal to produce zero output.
• If P < ATC, then profits will be negative.
(bunches) (CFA Francs) (CFA Francs) (CFA Francs) (CFA Francs(CFA Francs) (CFA Francs)
© 2014 by McGraw-Hill Education 11
Deciding when to operate
• When deciding the quantity to produce, a firm
additionally must decide whether to:
– Produce.
– Shut-down in the short-run.
– Exit the market in the long-run.
© 2014 by McGraw-Hill Education 12
Deciding when to operate
• When a firm shuts down production, it avoids
incurring variable costs.
– Fixed costs remain and are sunk in the short-run.
– Because fixed costs are sunk, they are irrelevant in
deciding whether to shut down in the short-run.
• The short-run decision to produce depends on
variable costs, not fixed costs.
• The long-run decision to produce depends on
total cost, since all costs are variable in the
long-run.
5© 2014 by McGraw-Hill Education 13
The short-run supply curve and the
shutdown rule
The short-run shutdown rule is to produce if
price is higher than AVC.
1,000
600
0 2 4
MC
AVC
Plantains (bunches)
Price (CFA Francs)
1. Whenever P > AVC the firm
will produce along the point
where P =MC, its short-run
supply curve, because revenue
exceeds variable cost.
Shutdown point
PAbove
Short-run
supply
curve
PShutdown
2. However, once the price
is below the minimum of
the AVC, the firm will not
produce because doing so
would generate a negative
profit
© 2014 by McGraw-Hill Education 14
The long-run supply curve and the
shutdown rule
Since all costs are variable in the long-run, the long-run
shutdown rule is to produce only if price is greater than
ATC.
1,000
860
0 43.3
MC
AVC
Plantains (bunches)
Price (CFA Francs)
PAbove
Long-run
supplycurve
Exit point
In the long
run, firms will
supply only if
price is above
ATC.
When prices
are below
ATC, the firm
will exit the
market.
PExit
ATC
© 2014 by McGraw-Hill Education 15
Active Learning: Supply curves and
operation decisions
Identify the shutdown point, the exit point, and
the SR and LR supply curves.
0
MC
AVC
Quantity
Price
ATC
6© 2014 by McGraw-Hill Education 16
Firm and market supply curves
• The firm’s supply curve is its marginal cost.
• The market supply curve is the sum of each firm’s
supply curve.
Firm supply: one firm
0
200
400
600
1,000
1,200
1,400
1 2 3 4 5 6
Plantains (bunches)
Price (CFA Francs)
Market supply: 100 firms
0 100 400 500 600
Market supply
300200
Firm supply
Price (CFA Francs)
Plantains (bunches)
800
200
400
600
1,000
1,200
1,400
800
Below a price of
620, each firm
will shut down,
resulting in no
production.
A firm only produces above its AVC. Given a fixed number of firms, the
market supply curve is established.
© 2014 by McGraw-Hill Education 17
Long-run supply
• The key difference between short-run and long-run
supply is that firms are able to enter and exit the
market in the long run.
• If positive economic profits exist:
– P > ATC.
– New firms enter to gain profits.
– The market supply curve shifts outward until P = ATC.
– Economic profits go to zero for all firms.
• If negative economic profits exist:
– P < ATC.
– Some firms exit the market.
– The market supply curve shifts inward until P = ATC.
– Economic profits go to zero for all firms.
© 2014 by McGraw-Hill Education 18
Long-run supply
• The process of market entry and exit causes
firms in a perfectly competitive market to earn
zero economic profits in the long run.
– In the long-run, price = min(ATC) = MR = MC.
– Accounting profits are positive in the long run.
– Firms earn an accounting profit to compensate
them for their opportunity cost.
7© 2014 by McGraw-Hill Education 19
Long-run supply
Because all firms operate at the point where
price = min(ATC), firms in a competitive market
operate at an efficient scale.
0
MC
ATC
Plantains (bunches)
Price (CFA Francs)
MR
e
Pe
Q
A firm’s efficient
scale is at the
quantity where
ATC=P=MC.
© 2014 by McGraw-Hill Education 20
Long-run supply
Given that P = min(ATC), price is the same at any
quantity in the long run.
Pe
0 Plantains (bunches)
Price (CFA Francs)
Supply
• If anything causes the market
equilibrium to move away
from this price, the resulting
positive or negative profits will
cause firms to enter or exit
the market until zero
economic profits are restored.
• The long-run supply curve is
horizontal, or perfectly elastic.
© 2014 by McGraw-Hill Education 21
Why the long-run market supply curve
shouldn’t slope upward, but does
• The competitive market theory suggests that the
market supply curve should always be perfectly
elastic.
• Most long-run market supply curves are upward
sloping.
– This is due to the assumption that all firms have the
same cost structure.
• If new entrants have a higher cost than existing
firms, price must rise sufficiently to entice new
firms to enter the market.
– Causes the long-run supply curve to be upward
sloping.
8© 2014 by McGraw-Hill Education 22
Long-run economic profits
• The competitive market theory suggests that
all firms should earn zero economic profit in
the long-run.
• In reality, price = min(ATC) for only the least-
efficient firms in the market.
– Typically, this is the last firm to enter the market.
– More efficient firms with lower ATC earn positive
economic profit in the long-run.
© 2014 by McGraw-Hill Education 23
2. and
average total
cost of
production
1. Changing
variable costs
decrease marginal
cost of production.
Market entry due to changing production
costs
Improved technology and production capabilities
lowers MC and ATC.
Pe
0 Qe
MC1
ATC1
Plantains (bunches)
Price (CFA Francs)
MR
3. Minimum ATC drops below
the market price, and there is
room for firm entry, because
whenever ATC < MR, profit is
possible
MC2
ATC2
• Innovative firms search for
better production
processes and new
technologies that enable
them to produce goods at
lower cost.
- Lowers MC and ATC.
• Positive profits entice
entrants.
• Price falls with production
costs.
© 2014 by McGraw-Hill Education 24
Responding to shifts in demand
Suppose the demand for a perfectly competitive
good increases; what happens in the short and long
run?
Pe Pe
0
Plantains (bunches)
0
Plantains (bunches)
D2
S1
SL
1. New firms enter,
shifting the supply curve
right.
S2
2. Equilibrium quantity
increases; price
returns to long-run
equilibrium.
Pe
0
D1
S1
SL
Plantains (bunches)
D2
S1
SL
1. Increase in demand
shifts the demand curve
right.
2. Equilibrium
price and
quantity
increase.
Market is in long-run
equilibrium.
Higher price causes
short-run profits.
D1
Market has new long-
run equilibrium.
9© 2014 by McGraw-Hill Education 25
Summary
• Perfectly competitive markets are defined by:
– There is a large number of buyers and sellers.
– No one buyer or seller can affect the market price.
– There is a standardized good or service.
– No barriers to entry exist.
• Firms maximize profit by producing at the
point where MR = MC.
© 2014 by McGraw-Hill Education 26
Summary
• Firms are able to enter and exit the market.
– If economic profits are positive, firms enter the market
and the supply shifts outward until profits are zero.
– If economic profits are negative, firms exit the market
and the supply shifts outward until profits are zero.
• In the long-run:
– Firms earn zero economic profits.
– Firms operate at their efficient scale.
– Supply is perfectly elastic.
© 2014 by McGraw-Hill Education 27
Summary
• If firms have different costs of production, the
long-run supply curve will be upward sloping.
• If firms innovate, the cost of production
decreases and price decreases as well.
• If the demand for a perfectly competitive good
increases, then short-run positive profits
induce entry of new firms and the supply shifts
out, causing a higher quantity of goods to be
produced at the same price.