Market Equilibrium
Class 12 · Economics
4 ideas in Class 12 Economics, explained in plain words, with games and quizzes to practise.
When Markets Clear
Part of: How Prices Settle
Equilibrium is the price where the quantity buyers want equals the quantity sellers offer, so the market clears. Below it buyers chase too little stock and push price up; above it sellers sit on unsold stock and cut price.
Why it matters. Every bazaar bargain follows this logic. Knowing the pull toward balance explains why prices move.
Key words
- Equilibrium price
- : The price where quantity demanded equals quantity supplied.
- Equilibrium quantity
- : The amount bought and sold at the clearing price.
- Excess demand
- : Wanted quantity above offered quantity at a low price.
- Excess supply
- : Offered quantity above wanted quantity at a high price.
Try it in two minutes
- Offer 5 toffees to 8 claimants and watch bids rise.
- Offer 8 toffees to 5 takers and watch the price slide.
- Match 6 toffees with 6 takers to show clearing.
- Name the price where plans matched.
Try at home. Track one vegetable price for a week and link each move to short or surplus stock.
Working Out Equilibrium Numbers
Part of: How Prices Settle
With demand 150 minus price and supply 50 plus price, setting them equal gives price 50 and quantity 100. Off balance, gaps are simple subtractions: at price 40 the gap is 20 of excess demand, at 60 it is 20 of excess supply.
Why it matters. Equations turn arguments about prices into checkable sums. One solution settles what fair price clears the market.
Formulas
- qD = qS at equilibrium
- ED = qD - qS
- ES = qS - qD
Key words
- Demand rule
- : Wanted quantity written as a function of price.
- Supply rule
- : Offered quantity written as a function of price.
- Clearing price
- : The price solving the demand-supply equality.
Try it in two minutes
- Write both rules for price 50 and compare the two quantities.
- Drop the price to 40 and measure the shortage.
- Raise the price to 60 and measure the surplus.
- Solve the equality together step by step.
Try at home. Pick any two simple rules, solve for the crossing price, and test one price above and below.
Shifts, Entry and the Labour Market
Part of: Shifts and Controls
A rightward demand shift lifts both price and quantity while a rightward supply shift lifts quantity but cuts price. With free entry, firms flood in until price equals minimum average cost, so extra demand only raises quantity and firm count.
Why it matters. Income rises, input costs jump and firms enter daily. Shift logic predicts who gains before prices settle.
Formulas
- n0 = q0 / q0f for the firm count
Key words
- Demand shift
- : Whole demand curve moving with income or tastes.
- Supply shift
- : Whole supply curve moving with costs or firm count.
- Normal profit
- : Earnings just covering all costs including the owner.
- Minimum average cost
- : The lowest per-unit cost anchoring free-entry price.
Try it in two minutes
- Shift one curve right on paper and find the new crossing.
- Shift supply right and watch price fall as quantity rises.
- Let new sellers enter until profits normalise.
- Compare fixed-firm and free-entry outcomes.
Try at home. Follow one crop from good rains to market and note which curve moved and where price went.
Ceilings, Floors and Fair Shares
Part of: Shifts and Controls
A ceiling caps price below balance to help buyers but leaves shelves short, forcing ration queues and tempting black markets. A floor props price above balance to help sellers but piles surplus the state must buy, as with minimum wages and crop support.
Why it matters. Good intentions misfire without gap arithmetic. Controls help only when the side effects are managed.
Key words
- Price ceiling
- : A legal maximum price set below balance.
- Price floor
- : A legal minimum price set above balance.
- Rationing
- : Sharing short supply by fixed quotas.
- Black market
- : Illegal sales above the capped price.
Try it in two minutes
- Cap a price below balance and count the queue.
- Prop a wage above balance and count the job seekers.
- List who gains and who queues in each case.
- Design a fair queue or buy-up for the gap.
Try at home. Find one controlled price nearby and ask who queues and who gains.
What your child will practise
- Ceilings, Floors and Fair Shares: Jungle Quick Fire (Quick Fire)
- Shifts, Entry and the Labour Market: Candy Quick Fire (Quick Fire)
- Shifts, Entry and the Labour Market: Space Puzzle (Clue Puzzle)
- When Markets Clear: Desert Quick Fire (Quick Fire)
- Working Out Equilibrium Numbers: Jungle Puzzle (Clue Puzzle)
- Quiz: Ceilings, Floors and Fair Shares (8 questions)
- Quiz: Shifts, Entry and the Labour Market (8 questions)
- Quiz: When Markets Clear (8 questions)
- Quiz: Working Out Equilibrium Numbers (8 questions)