Q.(a) 'Demand curve is the Average Revenue (AR) curve of a firm.' Do you agree? Discuss briefly, with reason in support of your answer.
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Market Equilibrium
Market Equilibrium: Where Buyers and Sellers Agree
Think of a busy vegetable market on a Saturday morning. Sellers have piled up tomatoes, potatoes, and onions. Buyers walk around, inspecting, bargaining. Some sellers price their tomatoes at ₹40 per kg; hardly anyone stops. Another seller keeps them at ₹20 per kg — a crowd forms, and within an hour, her stock is gone.
What you just witnessed is the market searching for a price that works for both sides. That price — where neither a pile of unsold tomatoes remains nor a long queue of disappointed buyers — is the equilibrium price.
The Precise Meaning
Market equilibrium is a state where the quantity that buyers want to buy (demand) exactly equals the quantity that sellers want to sell (supply) at the prevailing price. At this point, there is no tendency for the price to change — unless something outside the market shifts.
Qd=Qs
Where:
- Qd = Quantity demanded (what consumers wish to purchase at a given price)
- Qs = Quantity supplied (what producers wish to sell at that price)
This is the only price where the plans of all buyers and all sellers are consistent. No one is forced into an unwanted situation.
Why It Matters
Without equilibrium, markets are unstable. If price is above equilibrium, sellers produce more than buyers want — a surplus (excess supply). Unsold goods pile up, and sellers start cutting prices to clear stock. If price is below equilibrium, buyers want more than sellers produce — a shortage (excess demand). Queues form, and sellers realise they can raise prices.
The market automatically pushes toward equilibrium through price changes. This self-correcting mechanism is what Adam Smith called the "invisible hand." It means that in a free market, resources are allocated without a central planner telling anyone what to do.
NCERT Class-12 Macroeconomics (Chapter 5) defines equilibrium as: "A situation where aggregate demand equals aggregate supply." The same logic applies to a single market (micro) or the whole economy (macro).
A Diagram in Words
Picture a standard graph:
- The demand curve slopes downward (as price falls, quantity demanded rises).
- The supply curve slopes upward (as price rises, quantity supplied rises).
- They cross at one point — the equilibrium point.
Draw a vertical line from that point to the price axis: that's the equilibrium price. Draw a horizontal line to the quantity axis: that's the equilibrium quantity. The two curves meet only once because demand and supply move in opposite directions with price.
What NCERT Says (Class-12, Microeconomics, Chapter 5)
The textbook states clearly:
"Equilibrium price is the price at which the quantity demanded equals the quantity supplied. Equilibrium quantity is the quantity bought and sold at that price."
It also introduces two key terms:
- Excess demand — when Qd>Qs at a price below equilibrium. Competition among buyers pushes price up. …
Part (b)Concept understanding — Perfect Competition
Perfect competition is one of those ideas in economics that sounds technical but actually describes something you see every day — a market where no single seller has any real power, and the price is just… the price.
The everyday intuition
Think of a vegetable market in your town. There are dozens of vendors selling tomatoes. All the tomatoes are more or less the same. You can walk from one stall to another and buy from anyone. If one vendor tries to charge ₹10 more per kilo than the others, you simply walk to the next stall. That vendor loses customers instantly. So every vendor ends up charging the same price — the market price. No one decides it; it just emerges from everyone buying and selling.
That’s the core feel of perfect competition: price-takers, not price-makers.
The precise meaning
In economics, a market is called perfectly competitive when it satisfies five conditions. NCERT Class-12 (Introductory Microeconomics, Chapter 4) lists them clearly:
- Large number of buyers and sellers — so many that no single buyer or seller can influence the market price by their own action.
- Homogeneous product — the good sold by every firm is identical. No branding, no quality difference. A buyer has no reason to prefer one seller over another.
- Perfect information — every buyer and seller knows the price prevailing in the market. No one is tricked into paying more.
- Free entry and exit — any new firm can start producing and selling, and any existing firm can shut down and leave, without legal or cost barriers.
- No transaction costs — buyers and sellers can trade directly without extra expenses like transport or middlemen.
When all five hold, the market is perfectly competitive. In reality, no market is perfectly competitive — but agricultural markets, stock markets for widely traded shares, and online commodity markets come close.
Why it matters
Perfect competition is the benchmark — the ideal against which all real markets are compared. It tells us what happens when competition is at its maximum.
The key result is that in the long run, firms earn zero economic profit. That doesn’t mean they make no money — it means they earn just enough to cover all costs, including a normal return on their investment. If profits were positive, new firms would enter, supply would increase, price would fall, and profits would be squeezed back to zero. If losses occurred, firms would exit, supply would fall, price would rise, and losses would disappear.
This leads to two important outcomes:
- Productive efficiency: Firms produce at the lowest possible cost per unit (the minimum of the average cost curve).
- Allocative efficiency: The price equals the marginal cost of production — society gets exactly the quantity it values.
In a perfectly competitive market, the demand curve facing a single firm is a horizontal line at the market price. The firm can sell any quantity at that price, but nothing above it. This is why the firm is a price taker.
The revenue and profit picture (with a formula)
For a firm in perfect competition, the market price P is given. The firm’s total revenue is:
TR=P×Q
where Q is the quantity the firm sells. Since P is constant, each additional unit sold adds exactly P to revenue. So the marginal revenue MR is also P:
MR=P
The firm maximises profit by producing the quantity where MR=MC, where MC is marginal cost. Since MR=P, the profit-maximising rule becomes:
P=MC
This is the famous condition for a competitive firm’s equilibrium.
P=MC
- P = market price (constant for the firm)
- MC = marginal cost (the cost of producing one more unit)
The firm’s profit is:
π=TR−TC=(P×Q)−(ATC×Q)=(P−ATC)×Q
where ATC is average total cost. If P>ATC, the firm makes supernormal profit. If P=ATC, profit is zero (normal profit). If P<ATC, the firm incurs a loss.
A diagram in words …
Part (a)
- 'Demand curve is the AR curve.' Average revenue AR=QTR=QP×Q=P. Since AR equals price at every output, and the demand curve also plots price against quantity, the two coincide. Yes, I agree.
- Supply rises, demand unchanged. At the old price there is now excess supply, so price is bid down; along the curves quantity demanded expands and quantity supplied contracts until a new equilibrium. Equilibrium price falls and equilibrium quantity rises. …
- Yes — the demand curve is the AR curve since AR=P; and a supply increase with unchanged demand lowers equilibrium price and raises equilibrium quantity.
- Monopolistic competition has many sellers, product differentiation and free entry/exit (with selling costs).
Part (a)
- 'The demand curve is the AR curve of a firm.'
Average revenue is revenue per unit sold:
So AR is simply the price. The demand curve tells the price the firm can obtain for each quantity — which is exactly the average revenue at that output. Hence the demand curve and AR curve are one and the same (horizontal under perfect competition, downward-sloping under monopoly/monopolistic competition). I agree. Note the MR curve differs: for a falling demand curve MR lies below AR, since selling one more unit needs a price cut on all units.
AR=QTR=QP×Q=P
- Supply increases, demand unchanged. The market starts at price P∗, quantity Q∗ where demand meets supply. A rightward shift of supply, with demand unchanged, creates excess supply (a surplus) at P∗. This pushes price down; as price falls, quantity demanded rises (movement along the demand curve) and quantity supplied contracts (movement along the new supply curve) until the surplus clears at a new equilibrium.
- Equilibrium price falls.
- Equilibrium quantity rises. …
Showing the 12 most recent of 59 on this concept.
- CBSE 2026Set MARCH1 markQ.Price taking behaviour is the distinguishing characteristic of __________ market.
›Reveal solutionSolution
The blank is filled by Perfect Competition.
Under perfect competition there are so many firms, each producing an identical (homogeneous) product, that no individual firm's output is large enough to affect the market price. Every firm therefore takes the price as given by the market and can only decide how much to produce at that price. This 'price-taking' behaviour is the key characteristic that distinguishes perfect compe …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: In the ________ market a firm can enter and exit freely.
›Reveal solutionSolution
Free entry and exit is a feature of the perfectly competitive market.
In a perfectly competitive market, there is free entry and exit of firms — there are no barriers, so firms can enter when there are super-normal profits and leave when there are losses. This ensures that in the long run every firm earns only …
- CBSE 2026Set ANNUAL1 markMCQQ.Write True or False: In a perfectly competitive market firms are price-determinators.(a) True(b) False
›Reveal solutionSolution
False — firms in perfect competition are price-takers, not price-determinators.
Under perfect competition there are very many firms each selling a homogeneous product, and each firm's output is negligible relative to the market. Hence no firm can influence or set the price; it must accept (take) the price determined by overall market demand and supply. So firms are **p …
- CBSE 2026Set ANNUAL1 markMCQQ.In perfect competition, a firm-(a) determines price(b) accept price(c) Both(i) and(ii)(d) None of these(a) determines price(b) accept price(c) Both(i) and(ii)(d) None of these
›Reveal solutionSolution
A firm under perfect competition is a price-TAKER, accepting the market price.
Because a very large number of firms sell an identical (homogeneous) product under perfect competition, no single firm's output decision is large enough relative to the total market to influence the price. Each firm therefore faces a given, fixed market price and simply decides how MUCH to sell at that price — it 'accepts' the price rather than 'determining' it. This is the opposite of Monopoly/Olig …
- CBSE 2025Set MARCH1 markMCQQ.The Equilibrium price in a perfectly competitive market when free entry and exit is allowed.(a) P = Maximum of TR(b) P = Minimum of TR(c) P = Maximum of AC(d) P = Minimum of AC
›Reveal solutionSolution
With free entry and exit, long-run equilibrium price equals the minimum of the average cost curve — option (d).
…
- CBSE 2025Set MARCH1 markQ.Fill in the blank by choosing correct answer from the bracket (Financial, Government, RBI, Perfect competition, Product, Private): Price taking behaviour is the distinguishing characteristic of __________ market.
›Reveal solutionSolution
The blank is filled by 'Perfect competition'.
A perfectly competitive market has a large number of buyers and sellers, a homogeneous product, and free entry and exit. Because each firm is very small relative to the whole market, no single firm can affect the price by changing its own output. Every firm therefore takes the market-determined …
- CBSE 2025Set ANNUAL1 markMCQQ.Into how many periods has Marshall divided production time on the basis of supply? (A) Two (B) Three (C) Four (D) Seven
›Reveal solutionSolution
Marshall divided production/supply time into FOUR periods, so the answer is (C) Four.
In the Marshallian treatment of price determination, supply cannot react instantly; how much it can adjust depends on the time allowed. On this basis Marshall recognised four time periods: (1) the market or very short period (supply is fixed), (2) the short period (supply varies only by changing variable factors), (3) the long period (all factors variable, firms can enter/exit), and (4) the very long or secular period (even technology and population change). Thi …
- CBSE 2025Set ANNUAL1 markMCQQ.Market price is found in (A) Very short period market (B) Long period market (C) Very long period market (D) None of these
›Reveal solutionSolution
Market price is a very-short-period phenomenon, so the answer is (A) Very short period market.
Marshall distinguished market price from normal price. Market price is the actual price on a given day, determined when the stock of the good is fixed and supply cannot respond; demand is the dominant force, so the price can fluctuate sharply. In the long and very long periods supply fully adjusts and the price tends towards the nor …
- CBSE 2025Set ANNUAL1 markMCQQ.In equilibrium situation (A) The amount to be sold is equal to the amount to be purchased (B) Market supply is equal to market demand (C) Neither the firm nor the consumer wants to be destabilised (D) All of these
›Reveal solutionSolution
Every option describes equilibrium, so the answer is (D) All of these.
Equilibrium is a state of rest. At the equilibrium price the amount buyers want to purchase exactly equals the amount sellers want to sell, so market demand equals market supply, and neither firms nor consumers have any incentive to change their plans (no force pushing price up or down). Statements (A), (B …
- CBSE 2025Set ANNUAL1 markMCQQ.Price of a good is determined at a point where (A) Demand of the commodity is high (B) Supply of the commodity is high (C) Demand of the commodity and supply of the commodity are equal (D) None of these
›Reveal solutionSolution
Equilibrium price is set where demand equals supply, so the answer is (C).
In a competitive market the price is determined at the intersection of the demand and supply curves — the point where the quantity consumers are willing to buy equals the quantity producers are willing to sell. If demand merely being high (A) or supply being high (B) decided price, there would be persistent surpluses or shortages; price actually adjusts until the two are equal. This demand-supp …
- CBSE 2025Set ANNUAL1 markMCQQ.Market situation where there is only one buyer is (A) Monopoly (B) Monopsony (C) Duopoly (D) None of these
›Reveal solutionSolution
A market with a single buyer is a monopsony, so the answer is (B).
Market structures are classified by the number of buyers and sellers. Monopoly means a single seller; duopoly means two sellers. When there is only one buyer facing many sellers, the market is a monopsony — the lone buyer has buying (monopsony) power over price. A common real example is a single large employer in a local labour market. Hence the situation with only one buyer is monopsony. (Non-compet …
- CBSE 2025Set ANNUAL1 markMCQQ.In which market is product differentiation found? (A) Pure competition (B) Perfect competition (C) Monopoly (D) Monopolistic competition
›Reveal solutionSolution
Product differentiation is found in monopolistic competition, so the answer is (D).
In perfect and pure competition, all firms sell an identical (homogeneous) product, so there is no product differentiation. In monopoly there is a single firm and a single product, so differentiation does not arise either. Monopolistic competition has many firms selling closely related but differentiated products — distinguished by brand name, design, packaging, quality or advertising (for example, different brands of toothpaste or soap). This product differentiation gives each firm some control over its pr …
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