Supply and Demand: Core Concepts and Applications

Supply and Demand

Definitions and Core Concepts

• Demand: The quantity of a good or service that consumers are willing and able to purchase at various prices during a given period.

• Quantity Demanded (QD): The specific amount of a good consumers are willing to buy at a particular price.

• Supply: The quantity of a good or service that producers are willing and able to sell at various prices during a given period.

• Quantity Supplied (QS): The specific amount of a good producers are willing to sell at a particular price.

Demand vs. Quantity Demanded

• Demand: Refers to the entire relationship between price and quantity demanded, represented by the demand curve.

• Quantity Demanded: Refers to a single point on the demand curve at a specific price.

• Graphical Representation: Demand is the whole curve; quantity demanded is a point on the curve.

Creating a Market Demand Curve

• Add the quantity demanded by all consumers at each price to obtain the market demand curve (horizontal summation).

• Example: If at $10, Alice demands 2 units and Bob demands 3 units, market demand at $10 is 5 units.

The Law of Demand

• States that, ceteris paribus (all else equal), as the price of a good falls, the quantity demanded rises, and as the price rises, the quantity demanded falls.

Why the Demand Curve Slopes Downward

• Substitution Effect: As price falls, the good becomes relatively cheaper compared to substitutes, increasing quantity demanded.

• Income Effect: As price falls, consumers' purchasing power increases, allowing them to buy more.

Movements vs. Shifts in the Demand Curve

• Movement Along the Curve: Caused by a change in the price of the good itself (change in quantity demanded).

• Shift of the Curve: Caused by changes in non-price determinants (change in demand).

Change in Demand vs. Change in Quantity Demanded

• Change in Quantity Demanded: Movement along the demand curve due to a price change.

• Change in Demand: Shift of the entire demand curve due to changes in determinants other than price.

Causes of Movement Along the Demand Curve

• Only a change in the price of the good itself causes movement along the demand curve.

• Upward movement: decrease in quantity demanded.

• Downward movement: increase in quantity demanded.

Causes of Shifts in the Demand Curve

• Changes in non-price determinants cause the demand curve to shift.

• Rightward shift: increase in demand.

• Leftward shift: decrease in demand.

Determinants of Demand

• Income (normal and inferior goods)

• Prices of related goods (substitutes and complements)

• Tastes and preferences

• Expectations about future prices and income

• Number of buyers

Normal vs. Inferior Goods

• Normal Goods: Demand increases as income increases (e.g., organic food).

• Inferior Goods: Demand decreases as income increases (e.g., instant noodles).

Substitutes vs. Complements

• Substitutes: Goods that can replace each other (e.g., tea and coffee). An increase in the price of one increases demand for the other.

• Complements: Goods used together (e.g., printers and ink). An increase in the price of one decreases demand for the other.

Supply vs. Quantity Supplied

• Supply: The entire relationship between price and quantity supplied, represented by the supply curve.

• Quantity Supplied: The amount supplied at a specific price (a point on the supply curve).

Creating a Market Supply Curve

• Add the quantity supplied by all producers at each price (horizontal summation).

The Law of Supply

• States that, ceteris paribus, as the price of a good rises, the quantity supplied rises, and as the price falls, the quantity supplied falls.

Why the Supply Curve Slopes Upward

• Higher prices provide an incentive for producers to supply more due to higher potential profits.

Movements vs. Shifts in the Supply Curve

• Movement Along the Curve: Caused by a change in the price of the good itself (change in quantity supplied).

• Shift of the Curve: Caused by changes in non-price determinants (change in supply).

Change in Supply vs. Change in Quantity Supplied

• Change in Quantity Supplied: Movement along the supply curve due to a price change.

• Change in Supply: Shift of the entire supply curve due to changes in determinants other than price.

Causes of Movement Along the Supply Curve

• Only a change in the price of the good itself causes movement along the supply curve.

• Upward movement: increase in quantity supplied.

• Downward movement: decrease in quantity supplied.

Causes of Shifts in the Supply Curve

• Changes in non-price determinants cause the supply curve to shift.

• Rightward shift: increase in supply.

• Leftward shift: decrease in supply.

Determinants of Supply

• Input prices (cost of production)

• Technology

• Expectations about future prices

• Number of sellers

• Prices of related goods in production

Supply and Demand Together

• Both curves are plotted on the same graph: price on the vertical axis, quantity on the horizontal axis.

• The intersection determines market equilibrium.

Equilibrium

• Equilibrium Price: The price at which quantity demanded equals quantity supplied.

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

Determining Equilibrium Price and Quantity

• Graphically: The intersection point of the supply and demand curves.

• Mathematically: Set the demand equation equal to the supply equation and solve for price and quantity.

Example:

• Demand: $Q_D = 100 - 2P$

• Supply: $Q_S = 20 + 3P$

• Set $Q_D = Q_S$:

$100 - 2P = 20 + 3P$ $80 = 5P$ $P^* = 16$ $Q^* = 100 - 2(16) = 68$

Shortage and Surplus

• Shortage: Quantity demanded exceeds quantity supplied at a given price (below equilibrium).

• Surplus: Quantity supplied exceeds quantity demanded at a given price (above equilibrium).

• Graphical Representation: Shortage is below equilibrium; surplus is above equilibrium.

• Calculation:

At price $P_1$:

• Shortage: $Q_D - Q_S$

• Surplus: $Q_S - Q_D$

Effects of Shifts in Supply and Demand on Equilibrium

• Supply Increase (rightward shift): Equilibrium price falls, equilibrium quantity rises.

• Supply Decrease (leftward shift): Equilibrium price rises, equilibrium quantity falls.

• Demand Increase (rightward shift): Equilibrium price and quantity both rise.

• Demand Decrease (leftward shift): Equilibrium price and quantity both fall.

• Both Shift in Same Direction: Quantity changes, price is ambiguous.

• Both Shift in Opposite Directions: Price changes, quantity is ambiguous.

Summary Table: Shifts in Supply and Demand

Change	Equilibrium Price	Equilibrium Quantity
Increase in Demand	Increases	Increases
Decrease in Demand	Decreases	Decreases
Increase in Supply	Decreases	Increases
Decrease in Supply	Increases	Decreases
Increase in Demand & Supply	Ambiguous	Increases
Decrease in Demand & Supply	Ambiguous	Decreases
Increase in Demand, Decrease in Supply	Increases	Ambiguous
Decrease in Demand, Increase in Supply	Decreases	Ambiguous

Additional info: This summary expands on the provided outline with standard academic definitions, examples, and equations to ensure completeness and clarity for exam preparation.