⚖️ What Is Market Equilibrium?
Definition: Market equilibrium occurs where the demand curve and the supply curve intersect. At this point, the market clears — there is no surplus and no shortage.
The equilibrium price and quantity
Where D and S cross, we get two key values:
- Equilibrium price (Pₑ) — the price at which Qd = Qs
- Equilibrium quantity (Qₑ) — the amount bought and sold at that price
At equilibrium, every buyer who is willing to pay the market price finds a seller, and every seller willing to sell at that price finds a buyer. The market is in balance.
On diagrams, always mark the equilibrium point clearly with a dot or label (e.g. 'E'), and draw dashed lines from E down to Qₑ and across to Pₑ.
📊 What Happens Away From Equilibrium?
Excess supply (surplus)
If the price is above equilibrium, the quantity supplied exceeds the quantity demanded. Producers have unsold stock.
- Price is too high → Qs > Qd → surplus of goods
- Firms cannot sell everything → they cut prices to attract buyers
- Price falls back towards equilibrium
Excess demand (shortage)
If the price is below equilibrium, the quantity demanded exceeds the quantity supplied. Buyers cannot find enough goods.
- Price is too low → Qd > Qs → shortage of goods
- Buyers compete for limited stock → firms raise prices
- Price rises back towards equilibrium
Self-correcting markets: In a free market, surpluses push prices down and shortages push prices up. The market naturally adjusts towards equilibrium — this is the price mechanism at work.
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✏️ Drawing the Equilibrium Diagram
This is the most fundamental diagram in microeconomics. You will use it in almost every exam answer.
Step-by-step
- Draw axes: Price (P) on Y-axis, Quantity (Q) on X-axis
- Draw a downward-sloping demand curve labelled D
- Draw an upward-sloping supply curve labelled S
- Mark the intersection point as E (equilibrium)
- Draw dashed lines from E to both axes
- Label Pₑ on the Y-axis and Qₑ on the X-axis
- Add a title (e.g. 'Market for coffee')
Seven labels minimum: P axis, Q axis, D curve, S curve, equilibrium point E, Pₑ, Qₑ. Missing any of these loses marks.
Draw your curves with a slight curve (not perfectly straight lines). Real exam diagrams look more professional this way, and examiners appreciate it.
✅ Exam wording to memorise
- Equilibrium is the market-clearing price where Qd = Qs and there is no tendency for price to change
- Surplus: P above Pe → Qs > Qd → downward pressure on price until Pe
- Shortage: P below Pe → Qd > Qs → upward pressure on price until Pe
- Price mechanism functions: signalling, incentive, rationing
⚠️ Common mistakes
- Forgetting to write Qd = Qs (even if the diagram is correct)
- Not explaining WHY price changes (inventory builds up in a surplus; consumers bid up price in a shortage)
- Using demand language when explaining supply (and vice versa)
- Missing key diagram labels: axes, D, S, E, Pe, Qe