What is Price Ceiling, Price Floor, Shifts & End-of-Book Exercises in Class 12 Economics NCERT?

Interactive NCERT Class 12 Economics lesson on Price Ceiling, Price Floor, Shifts & End-of-Book Exercises

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Price Ceiling, Price Floor, Shifts & End-of-Book Exercises

🎓 Class 12 Economics CBSE Theory Chapter 5 — Market Equilibrium ⏱ ~30 min

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Class 12 · Introductory Microeconomics · Chapter 5 · Part 2 · Final Part

Applications: Price Ceilings, Price Floors, Shifts & Monopoly

Part 1 derived market equilibrium. Part 2 puts that machine to work. We see what happens when the government intervenes through a price ceiling (think PDS rice/wheat or rent control) or a price floor (think MSP for wheat or minimum wage). We then trace how a shift in demand alone, a shift in supply alone, or both shifting simultaneously change the equilibrium price and quantity. We close with a brief look at monopoly equilibrium — where MR < AR and the market produces less at a higher price than under perfect competition, generating a deadweight loss. Then we work all 25 NCERT exercises in full.

5.3 Application 1 — Price Ceiling (Maximum Price)

It is common for governments to fix a maximum allowable price for certain essential goods — wheat, rice, kerosene, sugar — when the market-determined price is judged to be too high for ordinary households to afford.

📖 Definition — Price Ceiling

A price ceiling^? is the government-imposed upper limit on the price of a good or service. To bite, the ceiling has to be set below the equilibrium price; otherwise the market would already trade at a price below the ceiling and the rule would be redundant.

5.3.1 Effect of a Price Ceiling on Equilibrium

Suppose the equilibrium price for wheat is p* and the equilibrium quantity is q*. The government fixes a ceiling at p_c < p*. At this lower controlled price:

Consumers want to buy q_c kilograms of wheat (more than at p*, because the price is lower).
Firms want to supply only q_c′ kilograms (less than at p*, because the price is lower).
The result is excess demand equal to (q_c − q_c′) — a shortage.

Figure 5.5 — Effect of a price ceiling. The ceiling p_c < p* creates a shortage equal to (q_c − q_c′). Consumers demand more, firms supply less.

5.3.2 Rationing & Black Markets

If buyers are willing to pay more than p_c but the law forbids the firm to charge more, how is the limited quantity q_c′ distributed among them? The standard policy answer is rationing: the government issues ration coupons, with each household entitled to a fixed quota purchased through the fair price shops (ration shops) of the Public Distribution System (PDS)^?. NCERT highlights two adverse consequences:

Long queues. Each consumer has to stand in line at the ration shop, paying a "time tax" on top of the controlled price.
Black markets. Households who cannot get enough at the ration shop will be willing to pay more — creating a parallel illegal market at prices above p_c.

Price Ceiling — Pros and Cons
Pros	Cons
Affordability for poor households on essential items (rice, wheat, kerosene)	Shortage emerges — q_c′ < q*
Stabilises consumption during inflationary spikes	Black markets, queues, and corrupt allocation
Politically equitable: same quota for every ration-card holder	Quality may decline as firms cut costs to stay above the ceiling
Used in India for rice, wheat, kerosene under the Essential Commodities Act, 1955	Long-run supply contracts further if firms exit altogether

5.3.3 Real-World Case — Rent Control in Indian Cities

Many Indian cities have at some point capped the rent that landlords may charge for residential apartments. The market rent p* at, say, Rs 25,000 per month is judged too high; the government caps rent at, say, Rs 12,000. Renters demand many more flats; landlords are reluctant to rent (some convert flats to commercial use, others let buildings deteriorate); and a black market emerges in the form of "deposits" or under-the-table payments.

Figure 5.6 — Stylised rent control: at the controlled rent ₹12,000, demanded apartments far exceed supplied apartments, generating a sustained shortage that worsens over the years as the gap widens.

5.4 Application 2 — Price Floor (Minimum Price)

For some goods, falling below a particular price level is judged undesirable. The government then sets a minimum price — a floor.

📖 Definition — Price Floor

A price floor^? is the government-imposed lower limit on the price that may be charged for a good or service. To bite, the floor has to be set above the equilibrium price; otherwise the market would already trade above the floor.

5.4.1 The Two Famous Examples

🌾

Agricultural Price Support — MSP

The Minimum Support Price (MSP)^? announced by the Government of India for crops such as wheat, paddy, pulses, and oilseeds. The Food Corporation of India (FCI) procures any surplus at the MSP and stocks it as a buffer.

⚒️

Minimum Wage Legislation

A statutory wage floor placed above the equilibrium wage. It guarantees decent earnings for unskilled workers but generates an excess supply of labour in the form of unemployment.

5.4.2 Effect of a Price Floor on Equilibrium

Suppose the equilibrium is (p*, q*). The government imposes a floor at p_f > p*. At this higher price:

Consumers want to buy only q_f (less than at p*).
Firms want to supply q_f′ (more than at p*).
Excess supply is (q_f′ − q_f).

To prevent the price from collapsing back to p*, the government must buy up the surplus at the floor price. That is exactly what FCI procurement of wheat and rice does each year.

Figure 5.7 — Effect of a price floor. The floor p_f > p* creates a surplus equal to (q_f′ − q_f). To sustain the floor price the government must procure the surplus.

Price Floor — Pros and Cons
Pros	Cons
Income security for farmers — stabilises rural earnings	Surplus output — wasteful overproduction
Builds buffer stocks for food security and PDS supply	Heavy fiscal cost of procurement and storage (FCI)
Decent wages for low-skilled workers (minimum wage)	Unemployment rises if minimum wage exceeds productivity at low-skill jobs
Cushions against world-price collapses for cash crops	Distorts cropping patterns — over-incentivises rice/wheat over pulses

Figure 5.8 — Stylised MSP vs. open-market wheat price (illustrative). When market price falls below MSP, FCI procurement props it up; when market price rises above MSP, MSP becomes redundant for that season.

5.5 Effect of Demand Shifts (Fixed Firms)

We now turn to comparative statics — how does the equilibrium change when one of the curves shifts? Begin with a shift in the demand curve, holding everything else (including the supply curve and the number of firms) constant.

5.5.1 Rightward Demand Shift

Take the initial equilibrium (p₀, q₀) at point E. Suppose demand shifts rightward to DD₂ — at every price the consumers want to buy more than before. At the old price p₀, there is now excess demand; price rises. At the new equilibrium G, both the price p₂ and the quantity q₂ are higher.

5.5.2 Leftward Demand Shift

If demand instead shifts leftward to DD₁, at every price consumers want less. At p₀ there is excess supply, so price falls. At the new equilibrium F, both p₁ and q₁ are lower.

⚙️ Rule for Demand Shifts (Fixed Firms)

Demand and equilibrium move in the same direction. Rightward shift ⇒ p ↑ and q ↑. Leftward shift ⇒ p ↓ and q ↓.

Figure 5.9 — Demand shifts. From E: a rightward shift to DD₂ moves equilibrium to G (higher p, higher q). A leftward shift to DD₁ moves equilibrium to F (lower p, lower q).

5.5.3 What Causes Demand Shifts?

Rising consumer income — for a normal good (like clothes) demand shifts right; for an inferior good demand shifts left.
Change in tastes & preferences — fashions change, demand follows.
More consumers in the market — population growth, urbanisation, festivals.
Price of related goods. If the price of a substitute (e.g. tea) rises, demand for the good (e.g. coffee) shifts right. If the price of a complement (e.g. cars) falls, demand for the related good (e.g. petrol) shifts right.

5.6 Effect of Supply Shifts (Fixed Firms)

5.6.1 Rightward Supply Shift

If supply shifts rightward to SS₁, at every price firms want to supply more. At the original price p₀ there is now excess supply; price falls. At the new equilibrium F, the price is lower but the quantity is higher.

5.6.2 Leftward Supply Shift

If supply shifts leftward to SS₂, at every price firms supply less. At p₀ there is now excess demand; price rises. At the new equilibrium G, price is higher but quantity is lower.

⚙️ Rule for Supply Shifts (Fixed Firms)

Supply and quantity move in the same direction; supply and price move in opposite directions. Rightward shift ⇒ p ↓ and q ↑. Leftward shift ⇒ p ↑ and q ↓.

Figure 5.10 — Supply shifts. Rightward shift (SS₁) lowers p and raises q; leftward shift (SS₂) raises p and lowers q.

5.6.3 What Causes Supply Shifts?

Technology improvement — same inputs produce more output, MC falls, supply shifts right.
Lower input prices — fertiliser becomes cheaper, MC falls, supply shifts right. Conversely, higher input prices shift supply left.
Government subsidies — effective MC for the firm falls, supply shifts right.
More firms entering the industry — at every price the market supplies more, supply shifts right (relevant in the long run).
Per-unit tax — effective MC for the firm rises, supply shifts left.

5.7 Simultaneous Shifts of Demand & Supply

What happens when both curves move at the same time? There are exactly four cases.

Table 5.2 — Impact of Simultaneous Shifts on Equilibrium (NCERT Table 5.1)
Shift in Demand	Shift in Supply	Quantity	Price
Leftward	Leftward	Decreases	May increase, decrease or remain unchanged
Rightward	Rightward	Increases	May increase, decrease or remain unchanged
Leftward	Rightward	May increase, decrease or remain unchanged	Decreases
Rightward	Leftward	May increase, decrease or remain unchanged	Increases

The pattern: when both curves shift in the same direction, the quantity effect is unambiguous and the price effect depends on magnitudes. When they shift in opposite directions, the price effect is unambiguous and the quantity effect depends on magnitudes.

Case (i): Both Right ↗↗

q ↑ for sure. p depends on relative size of shifts. If demand shift larger ⇒ p ↑; if supply shift larger ⇒ p ↓; if equal ⇒ p unchanged.

Case (ii): Both Left ↙↙

q ↓ for sure. p depends on relative size of shifts. Mirror image of case (i).

Case (iii): D Left, S Right ↙↗

p ↓ for sure. q depends on relative size of shifts. If supply shift larger ⇒ q ↑; if demand shift larger ⇒ q ↓.

Case (iv): D Right, S Left ↗↙

p ↑ for sure. q depends on relative size of shifts. Mirror image of case (iii).

Figure 5.11 — Simultaneous shifts case (i). When both demand and supply shift right by exactly equal amounts, equilibrium quantity rises while equilibrium price stays the same.

Figure 5.12 — Simultaneous shifts case (iii). With a leftward demand shift and a rightward supply shift of equal magnitude, the equilibrium price falls while quantity stays the same.

5.8 A Brief Note on Monopoly Equilibrium

So far our entire analysis has been within the perfectly competitive framework. The other extreme is monopoly^? — a market structure with a single seller and effective barriers to entry. Three quick points:

The monopolist faces the entire market demand curve, which slopes downward.
To sell one extra unit, the monopolist must lower price on every previous unit too. So marginal revenue is less than average revenue: MR < AR. Both slope downward, MR more steeply.
The profit-maximising rule is still MR = MC. But because MR < price, the chosen quantity q_m is smaller than the competitive quantity q_c, and the price p_m is higher than the competitive price p_c.

The shaded triangle between the demand curve, the MC curve and the two quantities is the deadweight loss^? of monopoly — the value of mutually-beneficial trades that could have happened under competition but do not happen under monopoly.

Figure 5.13 — Monopoly equilibrium. The monopolist sets MR = MC at q_m and charges p_m > p_c. The shaded triangle is the deadweight loss — efficient trades destroyed by monopoly pricing.

Activity 5.2 — MSP & the Buffer-Stock Debate

Look up the latest MSP for wheat or paddy announced by the Government of India.
Compare it with the current open-market wholesale price for the same crop in your state.
If MSP > market price, what should be happening to FCI procurement and buffer stocks? Discuss in pairs whether the system is helping farmers or distorting cropping patterns away from pulses, oilseeds and millets.

Sample observation: When MSP > market price, FCI procurement is heavy and buffer stocks pile up — sometimes far above PDS requirements. The MSP guarantee secures rice/wheat farmers' incomes (a clear pro), but the absence of comparable MSP support for pulses, millets and oilseeds skews land allocation toward water-intensive rice and wheat. This is a textbook example of a price floor's unintended distortion.

Competency-Based Questions — Applications & Shifts

Scenario: The Government of India announces a Minimum Support Price (MSP) of Rs 22 per kg for wheat. Suppose the wheat market demand curve is q^D = 1000 − 20p (in lakh tonnes) and the supply curve is q^S = 200 + 20p (in lakh tonnes). At the same time, an unrelated city imposes rent control on apartments — the controlled rent is Rs 8000/month against a market-determined equilibrium rent of Rs 18,000/month.

Q1. Find the wheat market's free-equilibrium price and quantity. Show that MSP = Rs 22 acts as a binding floor and compute the surplus the government will have to procure.

L3 Apply

Answer: Set q^D = q^S: 1000 − 20p* = 200 + 20p* ⇒ 40p* = 800 ⇒ p* = Rs 20. q* = 200 + 20×20 = 600 lakh tonnes. Since MSP Rs 22 > p* = Rs 20, the floor is binding. At p_f = 22: q^D = 1000 − 440 = 560, q^S = 200 + 440 = 640. Surplus = 640 − 560 = 80 lakh tonnes — this is what FCI must procure to sustain the MSP.

Q2. The rent-control case: at the controlled rent of Rs 8000 the apartment market generates a sustained shortage. Describe four economic and social side-effects you would expect, drawing on the textbook discussion.

L4 Analyse

Answer: (i) Persistent shortage — at Rs 8000 many more tenants demand flats than landlords supply, leading to long waiting lists. (ii) Black-market premiums — landlords demand non-refundable "deposits" or extra-legal payments to allocate scarce flats. (iii) Quality decline — landlords have weak incentive to maintain or repair flats whose rent cannot rise. (iv) Long-run supply contraction — some landlords convert residential flats to commercial use or refuse to rent at all, deepening the shortage over time. The intended beneficiaries (poor tenants) often lose out to insiders with information access; new entrants face the worst rationing.

Q3. Suppose simultaneously: (a) consumer income rises (rightward demand shift) and (b) a per-unit tax on wheat is imposed (leftward supply shift). Both shifts have equal magnitude. Predict the direction of change in equilibrium price and quantity, justifying with the simultaneous-shifts table.

L5 Evaluate

Answer: This is Case (iv): demand right + supply left. Price ↑ unambiguously; quantity may rise, fall or stay unchanged depending on relative magnitudes. With equal magnitudes the rightward pull on quantity from demand is exactly offset by the leftward pull from supply, so quantity stays at q*. Price, however, definitely rises because both shifts push price up. Verbal check: more buyers chasing fewer goods produced ⇒ higher price; the only ambiguity is whether the bigger crowd or the smaller harvest dominates the quantity story.

Q4 (HOT). Imagine a "perfectly competitive" wheat market is replaced by a single monopoly miller. Using the demand schedule q^D = 1000 − 20p and a constant marginal cost of MC = Rs 10, find (i) the monopoly price and quantity, (ii) the deadweight loss compared to the competitive outcome (where p = MC = Rs 10).

L6 Create

Answer: Inverse demand: p = 50 − q/20. So TR = pq = 50q − q²/20 ⇒ MR = 50 − q/10. Set MR = MC = 10: 50 − q/10 = 10 ⇒ q_m = 400 lakh tonnes. Substituting back: p_m = 50 − 400/20 = Rs 30. Competitive outcome (p = MC = 10): q_c = 1000 − 200 = 800 lakh tonnes. DWL = ½ × (q_c − q_m) × (p_m − MC) = ½ × 400 × 20 = 4000 lakh-rupee-units. Insight: monopoly halves the traded quantity and triples the price, generating a substantial welfare loss — which is why competition law and entry deregulation matter.

Assertion–Reason Questions — Applications & Shifts

Options for all items: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true, R is false. (D) A is false, R is true.

Assertion (A): Imposition of a price ceiling below the equilibrium price leads to a shortage in the market.
Reason (R): At the ceiling price, quantity demanded exceeds quantity supplied because consumers want more at a lower price while firms want to supply less.

Correct option: (A). Both true and R explains A. The ceiling forces price below the market-clearing level; consumers move down DD (more demanded) and firms move down SS (less supplied). The vertical gap between the two at the ceiling is the shortage.

Assertion (A): A rightward shift in the supply curve, with demand unchanged, lowers the equilibrium price and raises the equilibrium quantity.
Reason (R): At the original equilibrium price, the new supply exceeds demand, generating excess supply, which pushes the price down until a new market-clearing equilibrium is found at a higher quantity.

Correct option: (A). Both true; R is the precise mechanism by which A operates. This is the standard "supply-and-quantity move together; supply-and-price move opposite" rule.

Assertion (A): When demand and supply curves shift in opposite directions, the effect on equilibrium price is unambiguous but the effect on equilibrium quantity depends on the magnitudes of the shifts.
Reason (R): Opposite-direction shifts add their price effects (both push price the same way) but partly cancel their quantity effects.

Correct option: (A). Both statements true and R is the right explanation. With D right and S left, both shifts push price up; their quantity effects, however, are of opposite signs and the net depends on which shift is bigger. Same logic applies to D left + S right.

5.9 Chapter Summary

Ten Take-aways

In a perfectly competitive market, equilibrium occurs where market demand equals market supply.
With a fixed number of firms, p* and q* are jointly fixed at the intersection of DD and SS.
Each firm hires labour up to the point where Marginal Revenue Product of Labour equals the wage rate (w = MRPL = VMPL under perfect competition).
If demand shifts and supply is unchanged: rightward ⇒ p ↑, q ↑; leftward ⇒ p ↓, q ↓.
If supply shifts and demand is unchanged: rightward ⇒ p ↓, q ↑; leftward ⇒ p ↑, q ↓.
Same-direction simultaneous shifts: quantity effect unambiguous, price effect ambiguous.
Opposite-direction simultaneous shifts: price effect unambiguous, quantity effect ambiguous.
Under free entry & exit with identical firms, the long-run equilibrium price always equals the minimum of the firms' average cost — p = min AC.
With free entry-exit, demand shifts move only quantity and number of firms, never price; the quantity effect is more pronounced than under fixed firms.
A binding price ceiling (< p*) leads to excess demand; a binding price floor (> p*) leads to excess supply and requires government procurement.

Key Terms / Glossary

Key concepts of Chapter 5
Term	Meaning
Equilibrium	A situation where the plans of all consumers and firms in the market match — q^D(p) = q^S(p).
Excess Demand	Market demand exceeds market supply at a given price; ED(p) = q^D − q^S > 0.
Excess Supply	Market supply exceeds market demand at a given price; ES(p) = q^S − q^D > 0.
Marginal Revenue Product of Labour (MRPL)	MR × MPL — the extra revenue a firm earns from employing one more unit of labour.
Value of Marginal Product of Labour (VMPL)	p × MPL — under perfect competition this equals MRPL because MR = p.
Price Ceiling	Government-imposed upper limit on the price (below p*).
Price Floor	Government-imposed lower limit on the price (above p*).
Minimum Support Price (MSP)	Price floor the Indian government guarantees for major crops; FCI procures the surplus.
Walrasian Adjustment	Price-adjustment process: rises with excess demand, falls with excess supply.
Free Entry & Exit	Long-run assumption that firms can enter when there is profit and exit when there is loss; pins the long-run price at min AC.
Monopoly	Market structure with a single seller; faces the entire downward-sloping demand curve and produces less at higher prices than a competitive market would.
Deadweight Loss (DWL)	Welfare loss from an inefficient outcome (e.g. monopoly or binding price control); area between supply, demand and the new traded quantity.

NCERT Exercises — Full Model Answers

Q1. Explain market equilibrium.

A market is in equilibrium at the price p* at which the aggregate quantity that all firms wish to sell equals the aggregate quantity that all consumers wish to buy. Mathematically, q^D(p*) = q^S(p*). Graphically, this is the point of intersection of the market demand curve and the market supply curve. The traded quantity at this price is the equilibrium quantity q*. At p* there is neither excess demand nor excess supply, so there is no tendency for the price to change.

Q2. When do we say there is excess demand for a commodity in the market?

There is excess demand at a particular price when, at that price, the market demand for the commodity exceeds the market supply. Algebraically, ED(p) = q^D(p) − q^S(p) > 0. This happens at any price below the equilibrium price. The Walrasian Invisible Hand then drives the price upward.

Q3. When do we say there is excess supply for a commodity in the market?

There is excess supply at a particular price when, at that price, the market supply of the commodity exceeds the market demand. Algebraically, ES(p) = q^S(p) − q^D(p) > 0. This happens at any price above the equilibrium price; firms cannot sell their unsold stock and lower the price.

Q4. What will happen if the price prevailing in the market is (i) above the equilibrium price? (ii) below the equilibrium price?

(i) Above p*: Quantity supplied exceeds quantity demanded — there is excess supply. Some firms cannot sell their planned output and lower the price. As price falls, q^D rises and q^S falls until the two are equal at p*. (ii) Below p*: Quantity demanded exceeds quantity supplied — there is excess demand. Some buyers offer higher prices to obtain the good. As price rises, q^D falls and q^S rises until they are equal at p*. In both cases the market self-corrects toward equilibrium.

Q5. Explain how price is determined in a perfectly competitive market with fixed number of firms.

With a fixed number of firms, the market demand curve DD slopes downward and the market supply curve SS slopes upward. The equilibrium is the unique price-quantity pair (p*, q*) at which DD intersects SS — i.e. q^D(p*) = q^S(p*). At any price above p*, excess supply pushes price down; at any price below p*, excess demand pushes price up. Through this Walrasian adjustment, the market settles at p*. The corresponding quantity bought and sold is q*. Both p* and q* are jointly determined by the two curves.

Q6. Suppose the price at which equilibrium is attained in exercise 5 is above the minimum average cost of the firms constituting the market. Now if we allow for free entry and exit of firms, how will the market price adjust to it?

Since p* > min AC, every existing firm earns supernormal profit. With free entry, outside firms see this profit opportunity and enter the market, shifting the market supply curve rightward. The increase in supply pushes the market price down. Entry continues so long as p > min AC. When the price falls all the way to min AC, supernormal profits are wiped out and no further firm wishes to enter. The new long-run equilibrium price is exactly p₀ = min AC. The new equilibrium quantity is whatever DD says at this lower price — and a larger number of firms supplies it.

Q7. At what level of price do the firms in a perfectly competitive market supply when free entry and exit is allowed in the market? How is equilibrium quantity determined in such a market?

Under free entry-exit with identical firms, the long-run equilibrium price always equals the minimum of the average cost curve: p = min AC. Any price above this attracts entry and pushes price down; any price below this triggers exit and pushes price up. So entry-exit pins the price at min AC. The equilibrium quantity is then determined by what the market demand schedule yields at this price — i.e. q₀ = q^D(min AC).

Q8. How is the equilibrium number of firms determined in a market where entry and exit is permitted?

At p₀ = min AC each identical firm produces the same output q₀^f (the firm's output at minimum AC). The total market quantity at this price is q₀ = q^D(p₀). The equilibrium number of firms is the ratio: n₀ = q₀ / q₀^f. This is the number of firms required to supply the market quantity, with each firm producing its individual minimum-AC output.

Q9. How are equilibrium price and quantity affected when income of the consumers (a) increases? (b) decreases?

(a) For a normal good, an increase in consumer income shifts the demand curve rightward. With supply unchanged, at the old price there is now excess demand. The price rises until a new equilibrium is reached at higher p* and higher q*. For an inferior good, an income rise shifts demand leftward, lowering both p* and q*. (b) Symmetric: a fall in income shifts demand for a normal good leftward (p ↓, q ↓), and demand for an inferior good rightward (p ↑, q ↑). Under free entry-exit only the quantity changes; price stays at min AC.

Q10. Using supply and demand curves, show how an increase in the price of shoes affects the price of a pair of socks and the number of pairs of socks bought and sold.

Shoes and socks are complements — they are usually consumed together. An increase in the price of shoes raises the effective cost of using socks (because consumers buy fewer shoes and therefore need fewer socks). The demand for socks shifts leftward while the supply curve of socks is unchanged. At the original sock price there is now excess supply, so the equilibrium price of socks falls and the equilibrium quantity of socks bought and sold also falls. Diagrammatically, draw DD₀ and SS₀ for socks intersecting at E₀; shift DD leftward to DD₁; the new intersection F has lower p and lower q.

Q11. How will a change in price of coffee affect the equilibrium price of tea? Explain the effect on equilibrium quantity also through a diagram.

Coffee and tea are substitutes. If the price of coffee rises, consumers switch toward tea — the demand curve for tea shifts rightward. With supply of tea unchanged, at the old price of tea there is now excess demand. The equilibrium price of tea rises and the equilibrium quantity of tea bought and sold also rises. Diagrammatically: tea-market DD₀ and SS₀ intersect at E₀; shift DD₀ rightward to DD₁; the new intersection G has higher p and higher q. Conversely, a fall in the price of coffee shifts tea demand left and lowers both p and q in the tea market.

Q12. How do the equilibrium price and quantity of a commodity change when price of input used in its production changes?

An increase in the price of an input raises the marginal cost of production. The market supply curve shifts leftward. Demand is unchanged. At the old price there is excess demand; price rises and quantity falls. New equilibrium has higher p and lower q. A decrease in input price has the opposite effect: supply shifts right; price falls and quantity rises.

Q13. If the price of a substitute (Y) of good X increases, what impact does it have on the equilibrium price and quantity of good X?

An increase in the price of substitute Y makes Y costlier, so consumers shift their demand toward X. The demand curve for X shifts rightward. With supply of X unchanged, the equilibrium price of X rises and the equilibrium quantity of X also rises. (Same logic as Q11 with tea/coffee.)

Q14. Compare the effect of shift in demand curve on the equilibrium when the number of firms in the market is fixed with the situation when entry-exit is permitted.

With fixed firms, a rightward shift in DD raises both p* and q*. With free entry-exit, a rightward shift in DD raises only q* (and the number of firms n₀); price stays at p₀ = min AC. Under free entry-exit there is therefore (i) no price effect at all, and (ii) a larger quantity effect than under fixed firms, because the rise in DD is no longer partly absorbed by a price rise that depresses q^D. Symmetrically for leftward shifts.

Q15. Explain through a diagram the effect of a rightward shift of both the demand and supply curves on equilibrium price and quantity.

Draw DD₀ and SS₀ intersecting at E (p₀, q₀). Shift both curves rightward to DD₁ and SS₁. The new intersection E′ lies to the right of E — so q^* rises unambiguously. Whether p* rises, falls or stays the same depends on the relative magnitudes of the two shifts: if the demand shift is larger than the supply shift, p ↑; if supply shift is larger, p ↓; if they are equal, p is unchanged. So q ↑ definitely; p ambiguous.

Q16. How are the equilibrium price and quantity affected when (a) both demand and supply curves shift in the same direction? (b) demand and supply curves shift in opposite directions?

(a) Same direction: the effect on quantity is unambiguous (both shifts push quantity the same way), but the price effect depends on relative magnitudes. Both right ⇒ q ↑, p ambiguous. Both left ⇒ q ↓, p ambiguous. (b) Opposite directions: the effect on price is unambiguous (both shifts push price the same way), but the quantity effect depends on relative magnitudes. D right + S left ⇒ p ↑, q ambiguous. D left + S right ⇒ p ↓, q ambiguous. Refer to Table 5.1 for the full matrix.

Q17. In what respect do the supply and demand curves in the labour market differ from those in the goods market?

The roles of suppliers and demanders are reversed. In the goods market, firms supply and households demand. In the labour market, households supply labour (in hours) and firms demand labour. The "price" in the labour market is the wage rate w. The labour demand curve is downward-sloping (firms hire less when wages rise, by the law of diminishing marginal product). The market labour supply curve is upward-sloping in aggregate (more workers attracted by higher wages), although individual labour supply curves can bend backward at very high wages. The wage is determined at the intersection of the two curves.

Q18. How is the optimal amount of labour determined in a perfectly competitive market?

A profit-maximising firm hires labour up to the point where the marginal cost of hiring an additional worker equals the marginal benefit. The marginal cost is the wage rate w. The marginal benefit is the Marginal Revenue Product of Labour, MRPL = MR × MPL. So the rule is w = MRPL. Under perfect competition MR = price p, hence MRPL = p × MPL = VMPL (Value of Marginal Product of Labour), and the optimum condition becomes w = VMPL. As long as VMPL > w the firm gains by hiring one more worker; once VMPL falls below w the firm cuts back. The diminishing marginal product of labour ensures a downward-sloping demand curve for labour.

Q19. How is the wage rate determined in a perfectly competitive labour market?

The equilibrium wage rate w* is determined where the market labour demand curve (downward-sloping, derived by horizontally summing each firm's MRPL = w condition) intersects the market labour supply curve (upward-sloping, derived by aggregating the labour-supply choices of households). At this w*, the labour that all households together wish to supply equals the labour that all firms together wish to hire. At any wage above w* there is excess labour supply (unemployment) — wages fall. At any wage below w*, firms cannot find enough workers — wages rise. The market converges to (w*, l*).

Q20. Can you think of any commodity on which price ceiling is imposed in India? What may be the consequence of price-ceiling?

In India, price ceilings are imposed (under the Essential Commodities Act, 1955, and through the Public Distribution System) on items like rice, wheat, sugar and kerosene at fair-price (ration) shops. Other examples include rent control on residential property in cities like Mumbai. Consequences of a binding price ceiling: (i) excess demand and shortages; (ii) rationing through coupons, with long queues and time costs; (iii) emergence of black markets at illegal higher prices; (iv) decline in product quality; (v) in the long run, supply may shrink further as firms exit; (vi) corruption in the distribution chain. The intended benefit (affordability for the poor) is real but partly offset by these distortions.

Q21. A shift in demand curve has a larger effect on price and smaller effect on quantity when the number of firms is fixed compared to the situation when free entry and exit is permitted. Explain.

With fixed firms, a rightward demand shift creates excess demand. Price rises along the upward-sloping SS curve until equilibrium is restored. The price rise damps the quantity response (because higher price reduces q^D). So both p* and q* change, but each by a moderate amount. With free entry-exit, the same demand shift instead attracts new firms; their entry shifts SS right until the price returns to min AC. The entire excess demand is therefore absorbed through quantity expansion, with no price increase to dampen it. Hence the quantity effect is larger and the price effect is zero under free entry-exit.

Q22. Suppose the demand and supply curve of commodity X in a perfectly competitive market are given by: q^D = 700 − p; q^S = 500 + 3p for p ≥ 15, and 0 for 0 ≤ p < 15. Identify the reason behind the market supply being zero at any price less than Rs 15. What will be the equilibrium price? At equilibrium, what quantity of X will be produced?

The market supply is zero for p < 15 because at any such price each firm cannot cover its average variable cost (the shut-down condition from Chapter 4). The minimum AVC of the typical firm in this market is therefore Rs 15 — below this price every firm exits in the short run.

Equilibrium: Set q^D = q^S for p ≥ 15: 700 − p* = 500 + 3p* ⇒ 200 = 4p* ⇒ p* = Rs 50. Substitute: q* = 700 − 50 = 650 (also 500 + 3×50 = 650 ✓). So the equilibrium price is Rs 50 and the equilibrium quantity is 650 units of X.

Q23. Considering the same demand curve as in exercise 22, now let us allow for free entry and exit of identical firms producing commodity X. Each firm's supply is q_f^S = 8 + 3p for p ≥ 20, and 0 for 0 ≤ p < 20. (a) What is the significance of p = 20? (b) At what price will the market for X be in equilibrium? State the reason. (c) Calculate the equilibrium quantity and number of firms.

(a) p = 20 is the minimum of each firm's average cost curve. Below this price the firm earns less than normal profit and exits in the long run. So Rs 20 is also the long-run shut-down threshold for each firm.

(b) Under free entry-exit, the long-run equilibrium price always equals min AC, so p₀ = Rs 20. Any p > 20 attracts new firms, pushing supply right and price down to 20; any p < 20 triggers exit, pushing supply left and price up to 20. Only at p = 20 is there no entry-exit pressure.

(c) Equilibrium quantity from demand: q₀ = 700 − 20 = 680 units. Each firm supplies q₀^f = 8 + 3×20 = 68 units. Equilibrium number of firms n₀ = q₀ / q₀^f = 680 / 68 = 10 firms.

Q24. Suppose the demand and supply curves of salt are given by q^D = 1000 − p, q^S = 700 + 2p. (a) Find the equilibrium price and quantity. (b) Now suppose the price of an input rises so the new supply curve is q^S = 400 + 2p. How does equilibrium change? (c) Suppose the government imposes a tax of Rs 3 per unit of sale. How does it affect equilibrium?

(a) Set q^D = q^S: 1000 − p* = 700 + 2p* ⇒ 300 = 3p* ⇒ p* = Rs 100. Substitute: q* = 1000 − 100 = 900 (also 700 + 200 = 900 ✓). Equilibrium: (p*, q*) = (100, 900).

(b) New supply: q^S = 400 + 2p (leftward shift since at every p, q^S is now 300 less). Set q^D = q^S: 1000 − p* = 400 + 2p* ⇒ 600 = 3p* ⇒ p* = Rs 200. q* = 1000 − 200 = 800. New equilibrium: (200, 800). Higher price, lower quantity — exactly what supply-and-price-move-opposite predicts for a leftward supply shift. ✓

(c) A per-unit tax of Rs 3 raises each firm's effective MC by Rs 3, so the new supply curve is q^S′ = 700 + 2(p − 3) = 694 + 2p. Set q^D = q^S′ (using the original demand 1000 − p): 1000 − p* = 694 + 2p* ⇒ 306 = 3p* ⇒ p* = Rs 102. q* = 1000 − 102 = 898. So the price consumers pay rises from Rs 100 to Rs 102 (a Rs 2 increase) and quantity falls from 900 to 898. The Rs 3 tax is shared: consumers bear Rs 2 of it (price rises by 2) and producers absorb Rs 1 (net price they receive is 102 − 3 = Rs 99, down from Rs 100).

Q25. Suppose the market-determined rent for apartments is too high for common people to afford. If the government comes forward to help by imposing rent control, what impact will it have on the market for apartments?

Rent control is a price ceiling on apartments. The controlled rent is set below the equilibrium rent — otherwise it would not bite. At the controlled rent:
• Tenants demand more apartments than before (because rent is lower).
• Landlords are willing to supply fewer apartments (some hold flats vacant; some convert to commercial use; some refuse to maintain; new construction declines).
• Result: excess demand — a shortage.

Consequences observed in Indian cities: long waiting lists; black-market "deposits" or extra-legal premiums on top of the controlled rent; deteriorating quality of rental housing; reduced new supply over time as developers find rental housing unprofitable; and ironically, the policy often benefits incumbent middle-class tenants more than the truly poor (who lack access to the rationed flats). The intended benefit (affordability for the needy) is partly defeated by these distortions.

🎓

End of Class 12 Introductory Microeconomics

Chapter 5 — Market Equilibrium — completes the textbook.

Across five chapters we built up from scarcity and economic systems (Ch 1) → the consumer's choice (Ch 2) → the firm's production function (Ch 3) → the perfectly competitive firm's supply (Ch 4) → and finally to the market where consumers and firms meet (Ch 5). The toolkit you now possess — demand, supply, equilibrium, shifts, ceilings, floors, monopoly — is the foundation of every economic analysis you will ever do.

"Economics is everywhere, and understanding economics can help you make better decisions and lead a happier life." — Tyler Cowen

Frequently Asked Questions — Applications: Price Ceilings, Price Floors, Shifts & Monopoly

What is a price ceiling and what are its effects?

A price ceiling is a government-imposed maximum legal price set below the market equilibrium price, designed to protect consumers from high prices on essentials like kerosene or food grains. Because the legal price is below equilibrium, quantity demanded exceeds quantity supplied, creating excess demand and shortages. Governments typically respond with rationing — fixed quantities per ration card — and may also see black markets develop where the good is sold above the ceiling.

What is a price floor or minimum support price (MSP)?

A price floor is a government-imposed minimum legal price set above the market equilibrium, designed to protect producers — most commonly the minimum support price for crops like wheat, rice and sugarcane in India. Because the floor is above equilibrium, quantity supplied exceeds quantity demanded, creating excess supply (a surplus). The government typically procures the surplus at the support price, building food stocks for distribution and emergency reserves.

What happens to equilibrium price and quantity when demand shifts?

If demand rises (rightward shift) with supply unchanged, the equilibrium price and quantity both rise. If demand falls (leftward shift), the equilibrium price and quantity both fall. NCERT Class 12 illustrates this with diagrams: read the new equilibrium off the intersection of the new demand curve and the unchanged supply curve. Causes of demand shifts include income, taste, related-good prices and population.

What happens when supply shifts in market equilibrium?

If supply rises (rightward shift, e.g. better technology, lower input prices) with demand unchanged, equilibrium price falls and equilibrium quantity rises. If supply falls (leftward shift, e.g. drought, higher taxes), equilibrium price rises and quantity falls. The new equilibrium is read off the intersection of the new supply curve with the unchanged demand curve.

What happens with simultaneous shifts of demand and supply?

When demand and supply shift simultaneously, the change in equilibrium quantity is unambiguous if both shift in the same direction (both rise or both fall), but the change in price depends on which shift is larger. If both increase, quantity definitely rises; price may rise, fall or stay the same. NCERT Class 12 enumerates four cases (demand up/down combined with supply up/down) and gives the determinate and indeterminate signs of price and quantity in each.

What is the equilibrium of a monopoly firm?

A monopoly is a market with a single seller. Because the firm is the entire market, it faces a downward-sloping demand curve, so marginal revenue lies below average revenue. The monopolist maximises profit at MR = MC, then charges the price the demand curve permits at that quantity. NCERT Class 12 shows that monopoly equilibrium produces less output and a higher price than perfect competition — and may earn supernormal profit even in the long run because entry is blocked.

What sample NCERT Class 12 Chapter 5 exercises are covered here?

NCERT Class 12 Chapter 5 exercises ask students to derive equilibrium price and quantity from linear demand and supply schedules, analyse the effect of price ceilings and price floors with diagrams, predict the effect of demand and supply shifts, distinguish perfect competition from monopoly equilibrium, and compute equilibrium under free entry and exit. All exercises are answered in this part.

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