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Market Equilibrium – Class 12 Economics Chapter 5 Notes & NCERT PDF

Class 12EconomicsChapter 5NCERT book: Introductory Microeconomics - Economics Class 12

Notes and a simple summary of Chapter 5 of the NCERT Class 12 Economics book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 5: Market Equilibrium

Introduction

Chapter 5 brings together the consumer (Chapter 2) and the firm (Chapter 4). Market demand shows how much all consumers wish to buy at each price, and market supply shows how much all firms wish to sell. Market equilibrium is where these plans match. The chapter studies equilibrium with a fixed number of firms and with free entry and exit, the effect of shifts in demand and supply, wage determination in the labour market, and two applications of government price control: price ceiling and price floor.

Key Concepts

5.1 Equilibrium, Excess Demand, Excess Supply

  • Equilibrium: the plans of all consumers and firms match and the market clears: *qD(p) = qS(p). p is the equilibrium price and q* the equilibrium quantity.
  • Excess demand: market demand > market supply at a price (price below p*).
  • Excess supply: market supply > market demand at a price (price above p*).
  • Equilibrium is a situation of zero excess demand and zero excess supply.
  • Out-of-equilibrium behaviour: following Adam Smith, an 'Invisible Hand' raises price when there is excess demand and lowers it when there is excess supply, until equilibrium is reached.

    • 5.1.1 Fixed Number of Firms

    Equilibrium is at the intersection of the market demand curve DD and market supply curve SS. At price p1 below p, demand exceeds supply; unsatisfied consumers bid the price up. At p2 above p, supply exceeds demand; firms cut prices.

    Wage determination in the labour market. In the labour market, households supply labour and firms demand it (the opposite of the goods market). Labour means hours of work, not the number of workers.

  • A firm hires labour until w = MRPL, where MRPL = MR × MPL. For a competitive firm MR = p, so MRPL equals the value of marginal product (VMPL = p × MPL).
  • Because of diminishing MPL, a higher wage requires a higher MPL and hence fewer workers, so labour demand slopes downward.
  • An individual's labour supply reflects the income-leisure trade-off. A higher wage raises the opportunity cost of leisure (work more) but also raises income (enjoy more leisure). At high wages the second effect may dominate, giving a backward-bending individual supply curve. The market labour supply curve still slopes upward, as more people join the workforce.
  • The wage is set where labour demand equals labour supply.

    • Shifts with a fixed number of firms:

  • Demand shifts right (for example, rise in income for a normal good like clothes, or more consumers): price and quantity both rise. Demand shifts left: both fall. Price and quantity move in the same direction.
  • Supply shifts left (for example, rise in an input price): price rises, quantity falls. Supply shifts right (more firms): price falls, quantity rises. Price and quantity move in opposite directions.

    • Simultaneous shifts (Table 5.1):

  • Both shift left: quantity decreases; price may rise, fall or stay unchanged.
  • Both shift right: quantity increases; price may rise, fall or stay unchanged.
  • Demand left, supply right: price decreases; quantity is ambiguous.
  • Demand right, supply left: price increases; quantity is ambiguous.

    • When the curves shift in the same direction, the effect on quantity is certain; when they shift in opposite directions, the effect on price is certain.

    5.1.2 Free Entry and Exit

    With identical firms and free entry and exit, no firm earns super-normal profit or makes a loss in equilibrium. If price is above minimum AC, new firms enter, supply rises and price falls; if below, firms exit and price rises. So p = min AC. The equilibrium quantity is read from the demand curve at that price, and the number of firms n0 = q0 / q0f, where q0f is each firm's output at p0.

  • A rightward shift in demand leaves price unchanged at min AC but raises quantity and the number of firms; a leftward shift lowers them.
  • With free entry and exit, a demand shift has a larger effect on quantity and no effect on price, compared with a fixed number of firms.

    • 5.2 Applications

  • Price ceiling: a government-imposed upper limit on price, set below equilibrium for necessities (wheat, rice, kerosene, sugar). It creates excess demand (shortage). Goods are then distributed through rationing at ration (fair price) shops. Consequences: long queues and the growth of a black market.
  • Price floor: a government-imposed lower limit, set above equilibrium. Examples: agricultural price support and minimum wage legislation. It creates excess supply; under price support, the government must buy the surplus at the fixed price.

    • Worked Numericals

  • Example 5.1 (fixed firms). qD = 200 − p, qS = 120 + p (for p ≥ 10). Equating: 200 − p = 120 + p, so 2p = 80, *p = ₹40 and q* = 160 kg**.
  • Excess demand and supply in Example 5.1. ED(p) = 80 − 2p. At p = 25: qD = 175, qS = 145, so ED = 30 kg. ES(p) = 2p − 80. At p = 45: qS = 165, qD = 155, so ES = 10 kg.
  • Example 5.2 (free entry and exit). qD = 200 − p; each firm supplies 10 + p for p ≥ 20, so min AC = 20. p0 = ₹20, q0 = 200 − 20 = 180 kg, q0f = 10 + 20 = 30, and n0 = 180/30 = 6 firms.
  • Exercise 22. qD = 700 − p, qS = 500 + 3p (p ≥ 15). Supply is zero below ₹15 because that is the firms' minimum AVC (shut-down price). Equilibrium: 700 − p = 500 + 3p gives p = ₹50, q = 650.
  • Exercise 23. With free entry, each firm supplies 8 + 3p for p ≥ 20, so p = 20 is minimum AC. Equilibrium price = ₹20, quantity = 700 − 20 = 680, output per firm = 8 + 60 = 68, and number of firms = 680/68 = 10.
  • Exercise 24 (salt). (a) 1000 − p = 700 + 2p gives p = ₹100, q = 900. (b) After the input price rises, 1000 − p = 400 + 2p gives p = ₹200, q = 800: price up, quantity down, as expected for a leftward supply shift. (c) A tax of ₹3 per unit makes supply 700 + 2(p − 3) = 694 + 2p, so p = ₹102, q = 898.

    • Formula Sheet

  • Equilibrium: qD(p) = qS(p)
  • Excess demand ED(p) = qD − qS; excess supply ES(p) = qS − qD
  • Labour: w = MRPL = MR × MPL; competitive firm: w = VMPL = p × MPL
  • Free entry and exit: p0 = min AC; n0 = q0 / q0f
  • With a unit tax t on sellers, the supply function becomes qS(p − t)

    • Board Exam Focus

  • Explain market equilibrium and the adjustment through excess demand and supply (Exercises 1 to 5).
  • Free entry and exit: price = min AC and number of firms (Exercises 6 to 8, 14, 21).
  • Effect of income, related goods (shoes and socks, tea and coffee) and input prices on equilibrium (Exercises 9 to 13).
  • Simultaneous shifts with diagrams (Exercises 15, 16).
  • Labour market and wage determination (Exercises 17 to 19).
  • Price ceiling (rent control) and numericals (Exercises 20, 22 to 25).

    • Key Terms

  • Market equilibrium (बाज़ार संतुलन)
  • Equilibrium price (संतुलन कीमत)
  • Excess demand (अधिमाँग)
  • Excess supply (अधिपूर्ति)
  • Invisible hand (अदृश्य हाथ)
  • Marginal revenue product of labour (श्रम का सीमांत संप्राप्ति उत्पाद)
  • Value of marginal product (सीमांत उत्पाद का मूल्य)
  • Free entry and exit (निर्बाध प्रवेश और बहिर्गमन)
  • Price ceiling (उच्चतम निर्धारित कीमत)
  • Price floor (निम्नतम निर्धारित कीमत)
  • Rationing (राशनिंग)
  • Black market (काला बाज़ार)
  • Minimum wage (न्यूनतम मज़दूरी)

    • Common Mistakes

  • Setting a price ceiling above equilibrium. A binding ceiling is below equilibrium; a binding floor is above it.
  • Saying a demand increase raises price even with free entry and exit. Under free entry, price stays at min AC and only quantity and the number of firms change.
  • Claiming both price and quantity are certain when curves shift simultaneously. Only one of them is certain.
  • Treating households as buyers in the labour market. Households supply labour; firms demand it.
  • Forgetting to check the price range of supply functions (such as p ≥ 15) when solving numericals.

    • 💡 Key Learning Points

    • ✓Market equilibrium occurs where market demand equals market supply; excess demand pushes price up and excess supply pushes it down.
    • ✓With a fixed number of firms, demand shifts move price and quantity in the same direction, supply shifts move them in opposite directions; simultaneous shifts leave one of them ambiguous.
    • ✓With free entry and exit of identical firms, equilibrium price equals minimum average cost and the number of firms is q0/q0f; demand shifts change only quantity and the number of firms.
    • ✓In the labour market, firms hire until w = MRPL (= VMPL for competitive firms); labour demand slopes down and market labour supply slopes up.
    • ✓A price ceiling below equilibrium causes shortages, rationing and black markets; a price floor above equilibrium causes surpluses.

    👨‍🏫 Teaching Tips

    • →Run a classroom auction with buyer and seller cards to let students discover the equilibrium price.
    • →Solve Example 5.1 on the board, then ask students to compute excess demand at ₹25 and excess supply at ₹45.
    • →Use a four-row flowchart for simultaneous shifts and let students fill in which effect is certain.
    • →Explain free entry with a new chai stall appearing next to a profitable one.
    • →Connect the price ceiling to ration shops and the public distribution system familiar to students.
    • →Link the price floor to MSP for wheat and the minimum wage to make applications concrete.
    • →Draw the backward-bending individual labour supply curve and contrast it with the upward-sloping market curve.

    📋 Assessment Questions

    1. Can the student define equilibrium, excess demand and excess supply and explain price adjustment?
    2. Can the student predict the effect of single and simultaneous shifts of demand and supply?
    3. Can the student solve for equilibrium price, quantity and number of firms under free entry and exit?
    4. Can the student explain how the wage rate and optimal labour employment are determined?
    5. Can the student analyse the effects of a price ceiling and a price floor with diagrams?

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    Keep learning

    All chapters in Introductory Microeconomics - Economics Class 12

    1. 1. Introduction
    2. 2. Theory of Consumer Behaviour
    3. 3. Production and Costs
    4. 4. The Theory of the Firm under Perfect Competition
    5. 5. Market Equilibrium