Microeconomics · StudentHub Lesson
Market Equilibrium
How supply and demand interact to set the market-clearing price and quantity.
What you will learn
- Define market equilibrium price and quantity
- Explain how surpluses and shortages push markets toward equilibrium
- Analyze how shifts in supply or demand change equilibrium
- Understand allocative and productive efficiency in competitive markets
- Interpret price signals in a graph
Watch the lesson
Markets, Efficiency, and Price Signals: Crash Course Economics #19 · CrashCourse
Watch on YouTubeTopic notes
Main Idea
Equilibrium is where the supply and demand curves intersect — the price at which quantity supplied equals quantity demanded, so the market 'clears' with no shortage or surplus.
Key Concepts
- Equilibrium price: the price where supply meets demand
- Surplus: when price is above equilibrium, quantity supplied exceeds quantity demanded, pushing price down
- Shortage: when price is below equilibrium, quantity demanded exceeds quantity supplied, pushing price up
- Efficient markets: allocative efficiency (goods go to those who value them most) and productive efficiency (goods made at lowest cost)
- Shifts in either curve move the equilibrium point
Diagram (described)
On a Price-Quantity graph, the downward demand line crosses the upward supply line at one point — that intersection is equilibrium (P, Q). Above P, a horizontal gap between the curves shows a surplus; below P, the gap shows a shortage.
Example Logic
If demand increases (curve shifts right) while supply stays fixed, the new equilibrium has both a higher price and higher quantity.
Common Mistakes
- Assuming equilibrium price is always 'fair' or fixed forever — it changes when curves shift
- Confusing a surplus with a shortage
- Forgetting that markets self-correct through price changes, not government action
Key concepts
Important terms
- Equilibrium
- The price and quantity where supply equals demand, with no shortage or surplus.
- Surplus
- A situation where quantity supplied exceeds quantity demanded at a given price.
- Shortage
- A situation where quantity demanded exceeds quantity supplied at a given price.
- Allocative efficiency
- When resources are directed to produce the goods that society values most.
Worked examples
Problem
At a price of $5, quantity supplied is 100 units and quantity demanded is 60 units. Is this a surplus or shortage, and what will happen to price?
- 1. Compare quantity supplied (100) to quantity demanded (60)
- 2. Supplied > demanded means excess unsold goods
- 3. Sellers will lower price to sell surplus
Answer: It's a surplus; price will fall toward equilibrium
Quick revision
- Equilibrium = intersection of supply and demand curves
- Surplus occurs above equilibrium price
- Shortage occurs below equilibrium price
- Markets self-correct via price changes
- Shift in demand or supply creates a new equilibrium
- Competitive markets tend toward allocative and productive efficiency
Check your understanding
Question 1 · Multiple choice
Market equilibrium occurs where:
Question 2 · Multiple choice
If price is set above equilibrium, the result is a:
Question 3 · True or false
A shortage occurs when price is set above the equilibrium price.
Question 4 · Short answer
If demand for a good increases while supply stays the same, what happens to equilibrium price and quantity?
Question 5 · Multiple choice
Which best describes how markets typically resolve a shortage?
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