Supply and Quantity Supplied

Distinguishing Between a Change in Supply and a Change in Quantity Supplied

Understanding the difference between a change in supply and a change in quantity supplied is fundamental in microeconomics. These concepts are often confused but have distinct meanings and implications for market analysis.

• Change in Supply: Refers to a shift of the entire supply curve, caused by factors such as technology, input prices, or number of sellers. This means at every price, a different quantity is supplied.

• Change in Quantity Supplied: Refers to a movement along the supply curve, caused only by a change in the price of the good itself.

• Example: If the price of wheat rises, farmers supply more wheat (movement along the curve). If new technology makes wheat production cheaper, the supply curve shifts right (shift of the curve).

Graphical Analysis of Supply

Interpreting Supply Curve Movements

Supply curves can shift or experience movements along them, depending on market changes.

• Movement from S to S1: Represents an increase in supply (shift of the supply curve to the right).

• Causes of Supply Curve Shifts:

  • Improvement in technology

  • Decrease in input prices

  • Increase in the number of sellers

• Movement along the supply curve: Caused by a change in the price of the good itself.

Market Equilibrium

Definition and Determination

Market equilibrium is the point at which the quantity demanded equals the quantity supplied. This is where the supply and demand curves intersect.

• Equilibrium Price: Also called the market-clearing price, it is the price at which the intentions of buyers and sellers match.

• Equilibrium Quantity: The quantity bought and sold at the equilibrium price.

• Formula:

  • Set and solve for price () and quantity ().

• Example: If and , set to solve for and .

Market Adjustments: Surplus and Shortage

How Markets Respond to Disequilibrium

Markets naturally move toward equilibrium due to the actions of buyers and sellers.

• Surplus: Occurs when quantity supplied exceeds quantity demanded at a given price. This puts downward pressure on price.

• Shortage: Occurs when quantity demanded exceeds quantity supplied at a given price. This puts upward pressure on price.

• Adjustment Mechanism: Prices adjust until the market reaches equilibrium.

• Example: If the price of gum is above equilibrium, there will be a surplus, leading to price reductions.

Factors Affecting Equilibrium

Shifts in Demand and Supply

Changes in factors other than the price of the good can shift the demand or supply curves, affecting equilibrium price and quantity.

• Increase in Supply: Leads to a lower equilibrium price and higher equilibrium quantity.

• Increase in Demand: Leads to a higher equilibrium price and higher equilibrium quantity.

• Simultaneous Shifts: The effect on equilibrium price and quantity depends on the relative magnitude of the shifts.

• Example: If consumer income rises (for a normal good), demand increases, raising both equilibrium price and quantity.

Special Cases: Inferior and Normal Goods

Income Effects on Demand

Goods respond differently to changes in consumer income.

• Normal Goods: Demand increases as income increases.

• Inferior Goods: Demand decreases as income increases.

• Example: If potatoes are an inferior good, a decrease in consumer income increases demand for potatoes, raising both equilibrium price and quantity.

Signals in Market Allocation

Role of Prices

Prices act as signals that guide the allocation of resources in a market economy.

• Property Rights: Ensure that resources are used efficiently.

• Prices: Communicate information about scarcity and preferences, guiding producers and consumers.

Mathematical Applications: Solving for Equilibrium

Equilibrium with Linear Demand and Supply

To find the equilibrium price and quantity, set the demand and supply equations equal and solve for the variables.

• Example 1: ,

  • Set

  • Substitute into either equation to find :

• Example 2: ,

  • Set

Law of Demand and Law of Supply

Behavioral Foundations

The law of demand and the law of supply describe how consumers and producers respond to price changes.

• Law of Demand: As the price of a good increases, the quantity demanded decreases, ceteris paribus.

• Law of Supply: As the price of a good increases, the quantity supplied increases, ceteris paribus.

• Example: Alyssa rents more movies when the price falls from $3.00 to $2.50, demonstrating the law of demand.

Tabular Data: Market for Gum

Analyzing Surplus and Shortage

The following table shows the relationship between price, quantity demanded, and quantity supplied for gum. It helps illustrate how market price adjusts in response to surpluses and shortages.

• At 70¢ per pack: Quantity supplied exceeds quantity demanded (surplus), so price will fall.

• At 30¢ per pack: Quantity demanded exceeds quantity supplied (shortage), so price will rise.

Applied Example: Popcorn and Movie Ticket Markets

Market Shocks and Resource Allocation

When the price of popcorn rises due to increased demand for field corn (used for other purposes), farmers may shift production away from popcorn, reducing its supply and raising its price. This can also affect related markets, such as movie tickets, if popcorn is a complementary good.

• Popcorn Market: Supply decreases, price rises, quantity falls.

• Movie Ticket Market: If popcorn and movie tickets are complements, higher popcorn prices may reduce demand for movie tickets.

Additional info: Graphical illustrations would show a leftward shift of the supply curve for popcorn and a possible leftward shift of the demand curve for movie tickets.