2.4 The Interaction of Demand and Supply

2.4 The Interaction of Demand and Supply – Revision Notes

2.4.1 Market Equilibrium and Disequilibrium

Market Equilibrium

Market equilibrium occurs where the quantity demanded by consumers equals the quantity supplied by producers. At this point, the market is stable, and there is no tendency for price to change, assuming ceteris paribus (all other factors remain constant). This point determines the equilibrium price and equilibrium quantity.

• Equilibrium Price: The price at which demand and supply are balanced.

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

Graphically, this is the intersection point of the demand and supply curves.

Disequilibrium

Disequilibrium exists when there is either excess demand or excess supply:

• Excess Demand (Shortage): Occurs when the price is below equilibrium, and quantity demanded exceeds quantity supplied. This creates upward pressure on prices.

• Excess Supply (Surplus): Occurs when the price is above equilibrium, and quantity supplied exceeds quantity demanded. This puts downward pressure on prices.

The market will naturally adjust prices toward equilibrium through the price mechanism, correcting any imbalance.

2.4.2 Effects of Shifts in Demand and Supply Curves on Equilibrium

Demand Shifts

A shift in the demand curve (not movement along the curve) occurs when factors other than price change:

• Increase in demand (shift to the right): Leads to a higher equilibrium price and quantity.

• Decrease in demand (shift to the left): Leads to a lower equilibrium price and quantity.

Causes of demand shift include:

• Changes in income (normal vs inferior goods)

• Changes in taste and preferences

• Expectations of future prices

• Changes in population

• Price changes in related goods (complements or substitutes)

Supply Shifts

A shift in the supply curve results from changes in non-price determinants:

• Increase in supply (shift to the right): Results in a lower equilibrium price and higher quantity.

• Decrease in supply (shift to the left): Results in a higher equilibrium price and lower quantity.

Causes of supply shift include:

• Changes in production costs

• Technological improvements

• Taxes and subsidies

• Natural conditions (e.g., weather, disasters)

• Price of other goods

Combined Shifts

When both demand and supply shift simultaneously:

• If demand and supply both increase, quantity rises, but price change depends on magnitude.

• If demand increases and supply decreases, price will rise, and quantity change depends on relative strength.

• Diagrams are essential to visualize these effects accurately.

2.4.3 Relationships Between Different Markets

Joint Demand (Complements)

Two goods are in joint demand when they are used together. If the price of one rises, demand for both may fall. Example: Printers and ink cartridges.

• Price of Good A increases → Demand for Good B decreases (inverse relationship)

Alternative Demand (Substitutes)

Goods that satisfy the same need and can replace each other. Example: Tea and coffee.

• Price of Good A increases → Demand for Good B increases (positive relationship)

Derived Demand

Demand for a factor of production or input that results from demand for the final product. Example: Demand for steel is derived from demand for cars.

• If demand for cars increases → demand for steel increases

Derived demand is essential for analyzing factor markets and labor markets.

Joint Supply

When a production process yields multiple products simultaneously. Example: Producing beef also yields leather.

• An increase in beef production increases supply of leather, possibly lowering leather’s price

Joint supply explains how prices in one market can impact related goods in production.

2.4.4 Functions of Price in Resource Allocation

Price plays a crucial role in the allocation of scarce resources in a free market through three key functions:

1. Rationing Function

• Prices ration scarce resources.

• Higher prices limit demand to those most willing and able to pay.

• Example: In times of shortage (e.g., natural disasters), prices rise, reducing excess demand.

2. Signalling Function

• Prices signal information to both consumers and producers.

• A rising price indicates increased demand or reduced supply, signalling scarcity.

• A falling price indicates surplus or reduced demand.

Producers use these signals to allocate resources efficiently—for instance, shifting production toward higher-priced goods.

3. Incentivising Function

• Prices provide incentives to change behavior.

• Higher prices incentivise producers to increase output.

• Lower prices encourage consumers to buy more.

This function ensures responsiveness to market changes, promoting efficiency.

Conclusion

Chapter 2.4 provides a foundational understanding of how markets operate. Through analyzing equilibrium, shifts, market interrelationships, and the role of prices, students can grasp how real-world economic decisions are made. Price acts as a dynamic tool to balance supply and demand, reflect consumer preferences, and drive economic efficiency. Understanding these principles is crucial for any further study in microeconomics.