Understanding Supply and Price Determination in Economics

Extensions and Contractions (Movements)

A movement along the supply curve is caused only by a change in the price of the good itself.

• Extension in supply: When the price increases, the quantity supplied increases (a movement upward along the curve).
• Contraction in supply: When the price decreases, the quantity supplied decreases (a movement downward along the curve).

Shifts in the Supply Curve

A shift occurs when a factor other than price changes, causing the entire curve to move to a new position.

• Increase in supply: The curve shifts to the right (e.g., from $S_1$ to $S_2$), meaning more is supplied at every price level.
• Decrease in supply: The curve shifts to the left, meaning less is supplied at every price level.

Exam Tip: Always remember the term Ceteris Paribus. When we draw a supply curve, we assume that all other factors affecting supply are held constant.

Factors That Shift Supply

Several non-price factors can cause the supply curve to shift:

1. Costs of Factors of Production (FOPs): If the cost of land (rent), labour (wages), or capital (interest rates) rises, production becomes more expensive, causing supply to decrease (shift left). Conversely, a fall in production costs increases supply (shift right).
2. Government Policies:
   • Indirect Taxes: These increase business costs, causing a decrease in supply.
   • Subsidies: These are payments from the government that reduce business costs, causing an increase in supply.
3. Changes in Technology: Improvements in technology increase productivity and reduce unit costs, leading to an increase in supply.
4. External Shocks: Events such as extreme weather, wars, earthquakes, or diseases (like COVID-19) can disrupt production and decrease supply.
5. Resource Availability: The discovery of new resources increases supply, while the depletion of resources decreases it.

Market Equilibrium and Price Determination

When consumers (demand) and producers (supply) meet in a market, a price is "agreed" upon.

The Equilibrium Point

Market equilibrium is a state of equality where the quantity demanded by consumers exactly matches the quantity that firms are willing to supply. On a graph, this is the point where the demand curve and the supply curve intersect.

At this intersection, we find:

• Equilibrium Price ($P_1$): The price at which the market clears.
• Equilibrium Quantity ($Q_1$): The amount of the good bought and sold at the equilibrium price.

If non-price factors change (such as a change in consumer tastes or a change in technology), the curves will shift, and the market will move toward a new equilibrium price and quantity.

Market Disequilibrium: Surpluses and Shortages

If the market price is not set at the equilibrium level, the market is in disequilibrium. In a free market, the natural actions of buyers and sellers will eventually push the price back toward equilibrium.

Surplus (Excess Supply)

A surplus occurs when the market price is set above the equilibrium price.

• The Situation: At this high price, the quantity supplied exceeds the quantity demanded.
• The Result: Suppliers find themselves unable to sell their stock.
• The Correction: To clear the excess stock, suppliers will cut their prices. As prices fall, we see an extension in quantity demanded and a contraction in quantity supplied until equilibrium is restored.

Shortage (Excess Demand)

A shortage occurs when the market price is set below the equilibrium price.

• The Situation: At this low price, the quantity demanded exceeds the quantity supplied.
• The Result: Consumers are unable to buy all they want, often resulting in long queues.
• The Correction: With many buyers chasing too few goods, sellers respond by raising their prices. As prices rise, we see a contraction in quantity demanded and an extension in quantity supplied until the market reaches equilibrium again.