Explain how equilibrium price and quantity are set where demand equals supply, how surpluses and shortages are cleared by price, and how shifts in demand or supply change the equilibrium.

What this dot point is asking

This is where demand and supply come together. CCEA expects you to explain that the market price is set where demand equals supply, and to show what happens at any other price: a surplus above equilibrium and a shortage below it, both cleared by price. You must then use shifts in demand or supply to predict the new equilibrium price and quantity, and understand the price mechanism's job of rationing scarce goods and signalling to producers. This is the heart of Section 1 and the most heavily examined diagram skill in the course.

Market equilibrium

A market brings buyers and sellers together. The equilibrium price is the price at which the quantity consumers want to buy exactly equals the quantity producers want to sell. On a diagram, it is the point where the downward-sloping demand curve crosses the upward-sloping supply curve. The quantity traded at that price is the equilibrium quantity.

At equilibrium there is no pressure for the price to change: every buyer willing to pay that price finds a seller, and every seller willing to sell at that price finds a buyer. The market clears.

Surpluses, shortages and how price clears them

If the price is not at equilibrium, market forces push it there.

If the price is set above equilibrium, producers want to sell more than consumers want to buy, so there is a surplus (excess supply). Unsold goods pile up, so sellers cut the price. As price falls, demand extends and supply contracts until the surplus disappears at equilibrium.

If the price is set below equilibrium, consumers want to buy more than producers will supply, so there is a shortage (excess demand). Buyers compete for scarce goods and bid the price up. As price rises, demand contracts and supply extends until the shortage disappears at equilibrium.

The price mechanism

In a market economy, prices do the job of allocating scarce resources, often called the price mechanism or "invisible hand". It works through three roles. Prices ration scarce goods, because only those willing to pay get them. Prices signal to producers what consumers want: a rising price says "make more", a falling price says "make less". And prices give an incentive, because higher prices and profits attract resources into a market while lower prices drive them out. This is how a market answers what, how and for whom to produce without anyone being in charge.

Shifts in demand or supply change the equilibrium

When a non-price factor shifts a curve, the equilibrium moves. The method is always the same: decide which curve shifts, decide the direction, then read off the new price and quantity.

When only one curve shifts, the result is clear. An increase in demand raises both price and quantity; a decrease in demand lowers both. An increase in supply lowers price but raises quantity; a decrease in supply raises price but lowers quantity.

Why this matters

Price determination is the engine of the market system and the diagram you will draw most often. Every later topic that involves a market, from minimum wages and elasticity to taxes, subsidies and market failure, is analysed by shifting demand or supply and reading the new equilibrium. Examiners reward candidates who set out the shift clearly and, where two things change at once, who can say which result is certain and which is ambiguous.