Market Equilibrium and Efficiency
Demand and supply are the two forces that determine price and quantity in a free market. This unit covers the laws of demand and supply, determinants, shifts vs movements along curves, market equilibrium, the effect of government policies (tax, subsidy, price control) on equilibrium, and market efficiency measured by consumer and producer surplus.
In this chapter
Meaning of Demand
In economics, demand is more than mere desire — it is desire backed with willingness and ability to pay. The demand for a commodity is the quantity which consumers are able and willing to purchase at each possible price during a given period of time, other things remaining the same. The essential elements of demand are: price, desire, ability, willingness, and time period.
The Law of Demand
The law of demand states the inverse relationship between the quantity demanded and the price of a commodity. According to this law, the demand for a commodity increases with a fall in its price and decreases with a rise in its price, ceteris paribus. Thus, price and quantity demanded are inversely related, giving the demand curve its downward slope.
Demand function — inverse relationship
Determinants of Demand
Factors Shifting the Demand Curve
- Price of the good itself (movement along the curve, not a shift).
- Income of the consumer — normal goods (demand rises with income); inferior goods (demand falls with income).
- Price of related goods — substitutes (tea/coffee) and complements (tea/sugar).
- Tastes and preferences — fashion, habits, advertising.
- Population — more buyers mean more demand.
- Expectations of future price — buy now if you expect prices to rise.
Movement vs Shift
A movement along the demand curve is caused only by a change in the good's own price (change in quantity demanded). A shift of the entire demand curve is caused by a change in any non-price determinant (change in demand). Rightward shift = increase in demand; leftward shift = decrease in demand.
Exceptions to the Law of Demand
Cases Where Demand Curve Slopes Upward
- Giffen goods — inferior staple foods (e.g. plain rice for very poor households). When price rises, the income effect dominates: households cannot afford costlier substitutes, so they buy MORE of the cheap staple.
- Veblen goods — luxury status goods (designer watches, luxury cars). Higher price signals higher prestige, so demand rises.
- Price expectations — if consumers expect prices to rise further, a price rise today may trigger panic buying (e.g. salt, fuel during crises).
- Conspicuous consumption — goods bought to display wealth (jewellery, branded clothing).
- Ignorance — buyers judge quality by price; a higher price may signal higher quality and increase demand.
Nepal Example: Daal-Bhat and Remittance
In rural Nepal, daal-bhat (lentil-rice) is the staple. If rice prices spike, very poor households may cut back on vegetables and meat and eat even more rice — a quasi-Giffen pattern. Separately, rising remittance income (from Nepali workers in Gulf countries) shifts the demand curve for housing, motorbikes, and education rightward — these are normal goods for remittance-receiving households. NRB data show remittance inflow exceeding Rs 1,000 billion annually, dramatically changing consumption patterns in rural Nepal.
Individual Demand Schedule for a Commodity
| Price (Rs/unit) | Quantity Demanded (units/day) |
|---|---|
| 5 | 100 |
| 10 | 80 |
| 15 | 60 |
| 20 | 40 |
| 25 | 20 |
The Law of Supply
The law of supply states the direct relationship between the quantity supplied and the price of a commodity. As price rises, quantity supplied rises, and vice versa, ceteris paribus. This gives the supply curve its upward slope. The main reason is that higher prices give producers greater incentive and revenue to cover higher production costs.
Supply function — direct relationship
Determinants of Supply
Factors Shifting the Supply Curve
- Price of the good itself (movement along the curve).
- Price of inputs — wages, raw materials, fuel; higher input prices shift supply leftward.
- Technology — improvements shift supply rightward (more output per unit of input).
- Number of sellers — more producers mean more market supply.
- Government policy — taxes shift supply leftward; subsidies shift it rightward.
- Expectations of future prices — expecting higher future prices may reduce current supply.
- Natural conditions — weather, climate, disasters heavily affect agricultural supply.
Shift vs Movement in Supply
A movement along the supply curve is caused only by a change in the good's own price (change in quantity supplied). A shift of the supply curve is caused by changes in input prices, technology, number of sellers, taxes, or natural conditions (change in supply). Rightward shift = increase in supply; leftward shift = decrease in supply. Many students confuse these two — be careful in exams.
Market Equilibrium
Market equilibrium is the state in which quantity demanded equals quantity supplied. The equality of demand and supply gives the equilibrium price — the price at which the market clears with no shortage or surplus. The equilibrium quantity is the quantity both demanded and supplied at that price. Above equilibrium, surplus builds and pushes prices down; below it, shortage drives prices up.
Demand–Supply Schedule and Market Equilibrium
| Price (Rs/kg) | Quantity Demanded | Quantity Supplied | Surplus/Shortage | Pressure on Price |
|---|---|---|---|---|
| 5 | 50 | 10 | −40 (Shortage) | Upward ↑ |
| 10 | 40 | 20 | −20 (Shortage) | Upward ↑ |
| 15 | 30 | 30 | 0 (Equilibrium) | None ✓ |
| 20 | 25 | 40 | +15 (Surplus) | Downward ↓ |
| 25 | 20 | 50 | +30 (Surplus) | Downward ↓ |
Equilibrium price from linear demand and supply
Effects of Shifts in Demand and Supply
Effect of Demand and Supply Shifts on Equilibrium
| Change | Effect on Price | Effect on Quantity |
|---|---|---|
| Demand increases (rightward) | Rises ↑ | Rises ↑ |
| Demand decreases (leftward) | Falls ↓ | Falls ↓ |
| Supply increases (rightward) | Falls ↓ | Rises ↑ |
| Supply decreases (leftward) | Rises ↑ | Falls ↓ |
| Both demand and supply increase | Ambiguous | Rises ↑↑ |
| Both demand and supply decrease | Ambiguous | Falls ↓↓ |
Nepal Example: Vegetable Prices
In the Kalimati vegetable market, prices of tomatoes can swing from Rs 20 to Rs 80 per kg within weeks. During the Dashain festival, demand shifts rightward (more households buying), pushing prices up. After the 2015 earthquake, the supply curve shifted leftward in affected districts (farms damaged, transport disrupted), causing sharp price increases. During the COVID-19 lockdown, both effects occurred: supply chain disruption shifted supply leftward while restaurant closure shifted demand leftward — net effect varied by vegetable.
Effect of Government Policy on Equilibrium
Governments intervene in markets through taxes, subsidies, and price controls. A per-unit tax shifts the supply curve upward by the amount of the tax, raising the price buyers pay and lowering the price sellers receive — creating a deadweight loss. A subsidy shifts the supply curve downward, lowering the buyer's price and raising the seller's price. Price ceilings (maximum prices below equilibrium) create shortages; price floors (minimum prices above equilibrium) create surpluses.
Price Ceiling and Price Floor
Government Price Controls
- Price ceiling — legal maximum price set below equilibrium. Example: Nepal government's cap on cooking gas cylinder price. Intended to protect consumers, but creates shortage, black markets, and queues.
- Price floor — legal minimum price set above equilibrium. Example: minimum support price for paddy. Intended to protect producers, but creates surplus and government must buy the excess.
- Tax incidence — even if a tax is levied on sellers, both buyers and sellers share the burden. The more inelastic side pays a larger share.
- Subsidy — negative tax; lowers consumer price and raises producer price, encouraging over-production and over-consumption.
Common Misconception
A common student error is to assume that the statutory incidence of a tax (who legally pays) determines the economic incidence (who actually bears the burden). It does NOT — the burden depends on elasticities. If demand is inelastic and supply is elastic, buyers bear most of the tax even if sellers are legally required to remit it. Always check the relative slopes of demand and supply.
Market Efficiency: Consumer and Producer Surplus
Consumer surplus is the difference between what a consumer is willing to pay and what they actually pay — the area below the demand curve and above the price line. Producer surplus is the difference between the price a producer receives and the minimum price they would accept — the area above the supply curve and below the price line. The sum of consumer and producer surplus is the total economic surplus, which is maximised at the free-market equilibrium — hence free markets are said to be efficient.
Total economic surplus
Measurement of Consumer Surplus
For a discrete demand schedule, consumer surplus is the sum, over each unit consumed, of (willingness to pay − price paid). For a continuous linear demand curve P = a − bQ, consumer surplus at price P is the area of the triangle above P and below the demand line: CS = (1/2) × (maximum willingness to pay − P) × Q. The maximum willingness to pay is the price at which Q = 0, found by setting Q = 0 in the demand equation (giving P = a).
Consumer surplus — integral form and linear approximation
Producer Surplus
Producer surplus (PS) is the difference between the price a producer actually receives and the minimum price at which they would be willing to supply each unit (their marginal cost). Graphically, it is the area above the supply curve and below the market price line, up to the equilibrium quantity. For a linear supply curve P = c + dQ, at price P: PS = (1/2) × (P − c) × Q*, where c is the price at which Q = 0 (the shutdown price for marginal producers). Producer surplus measures the net benefit producers receive from participating in the market — it is closely related to profit, but does not deduct fixed costs.
Key Insight
At the free-market equilibrium, total surplus is maximised. Any government intervention (tax, price ceiling, price floor) that moves the market away from equilibrium creates a deadweight loss — a reduction in total surplus that nobody captures.
Key Terms and Definitions / मुख्य शब्द र परिभाषा
- Demand: Quantity consumers are able and willing to buy at each price — माग: उपभोक्ताले प्रत्येक मूल्यमा किन्न सक्षम र इच्छुक मात्रा।
- Supply: Quantity producers are able and willing to sell at each price — आपूर्ति: उत्पादकले प्रत्येक मूल्यमा बेच्न सक्षम र इच्छुक मात्रा।
- Law of demand: Price and quantity demanded are inversely related — मागको नियम: मूल्य र माग मात्रा विपरीत सम्बन्धमा।
- Law of supply: Price and quantity supplied are directly related — आपूर्तिको नियम: मूल्य र आपूर्ति मात्रा प्रत्यक्ष सम्बन्धमा।
- Equilibrium price: Price at which quantity demanded equals quantity supplied — सन्तुलन मूल्य: माग मात्रा आपूर्ति मात्रासँग बराबर हुने मूल्य।
- Ceteris paribus: Other things being equal — अन्य कुरा समान।
- Substitute goods: Goods that can replace each other — विकल्प वस्तु: एकआपसमा प्रतिस्थापन हुने वस्तु।
- Complementary goods: Goods used together — पूरक वस्तु: सँगै प्रयोग हुने वस्तु।
- Consumer surplus: Willingness to pay minus actual price — उपभोक्ता अधिशेष: तिर्न तयार रकम माइनस वास्तविक मूल्य।
- Producer surplus: Price received minus minimum acceptable price — उत्पादक अधिशेष: प्राप्त मूल्य माइनस न्यूनतम स्वीकार्य मूल्य।
- Deadweight loss: Loss of total surplus from market distortion — मृतभार हानि: बजार विकृतिबाट कुल अधिशेषको हानि।
- Price ceiling: Legal maximum price — मूल्य सीमा: कानूनी अधिकतम मूल्य।
Practice Problem
Given the demand function Q_d = 100 − 4P and the supply function Q_s = 20 + 2P, find the equilibrium price and quantity. Then verify that the market clears (no surplus or shortage).
Practice Problem
The demand and supply functions of a commodity are: Q_d = 200 − 5P and Q_s = 50 + 5P. (a) Find equilibrium price and quantity. (b) Calculate consumer surplus at equilibrium. (c) Calculate producer surplus at equilibrium. (d) What is the total economic surplus?