Class 11 Economics Chapter 11 Question Answer | Theory of Consumer Behaviour | English Medium

Class 11 Economics Chapter 11 Question Answer | Theory of Consumer Behaviour | English Medium | ASSEB

Welcome to HSLC Guru! In this article, we present a complete and exam-oriented study guide for Class 11 Economics Chapter 11 — Theory of Consumer Behaviour, prepared strictly according to the latest ASSEB (Assam State School Education Board) syllabus. This chapter forms the foundation of microeconomic analysis and explains how a rational consumer makes choices to maximise satisfaction within a limited budget. The notes include a detailed summary, all textbook questions with answers, additional MCQs, fill-in-the-blanks, true/false statements, and a glossary of key terms — everything required for thorough exam preparation in English Medium.

Chapter Summary

The Theory of Consumer Behaviour studies how a rational consumer allocates his/her limited income among various goods and services in order to obtain maximum satisfaction. The central concept here is utility, which means the want-satisfying capacity of a commodity. Economists analyse utility through two approaches. The cardinal utility approach, given by Alfred Marshall, assumes that utility can be measured in numerical units called “utils”. In contrast, the ordinal utility approach, developed by Hicks and Allen, holds that utility cannot be measured but can only be ranked or compared (first, second, third preference, etc.). Two important utility concepts are Total Utility (TU) — the sum of utilities derived from consuming all the units of a commodity, and Marginal Utility (MU) — the additional utility derived from consuming one more unit. The Law of Diminishing Marginal Utility states that as a consumer consumes more and more units of a commodity, the marginal utility derived from each additional unit goes on falling.

A consumer attains equilibrium when he/she derives maximum satisfaction from the given income and prices and has no tendency to change consumption pattern. Under the cardinal approach, in case of a single commodity the condition is MUx = Px × MUm; for multiple commodities the law of equi-marginal utility applies — MUx/Px = MUy/Py = MUm (marginal utility of money). Under the ordinal approach, equilibrium is achieved where the Indifference Curve (IC) is tangent to the budget line, i.e. MRSxy = Px/Py, along with the second-order condition that IC must be convex to the origin. An indifference curve is the locus of all combinations of two goods which yield equal satisfaction to the consumer. Its main properties are: it slopes downward from left to right, is convex to the origin (due to diminishing MRS), higher IC represents a higher level of satisfaction, and two ICs never intersect each other.

The budget line shows all combinations of two goods that a consumer can purchase by spending his entire income at given prices. Its equation is Px·X + Py·Y = M, and the slope is −Px/Py. The budget set is the collection of all bundles available to the consumer (those on or below the budget line). A change in the consumer’s income shifts the budget line parallel to itself, while a change in the price of any good rotates it. From the consumer equilibrium analysis, the demand curve is derived — it is the graphical representation of the relationship between price and quantity demanded. The Law of Demand states that, other things remaining constant, when the price of a commodity falls, its quantity demanded rises and vice-versa, giving rise to a downward-sloping demand curve. A movement along the demand curve occurs due to a change in the price of the good itself (extension/contraction), whereas a shift takes place due to changes in other factors like income, tastes, prices of related goods, etc.

Price Elasticity of Demand (Ed) measures the responsiveness of quantity demanded to a change in price. The formula is Ed = −(ΔQ/Q) ÷ (ΔP/P) or equivalently Ed = (ΔQ/ΔP) × (P/Q). The negative sign indicates the inverse relationship; for convenience the absolute value is taken. There are five degrees of elasticity — perfectly elastic (Ed = ∞), perfectly inelastic (Ed = 0), unitary elastic (Ed = 1), relatively elastic (Ed > 1), and relatively inelastic (Ed < 1). Methods of measurement include the percentage method, total expenditure method, and geometric (point) method. The major factors affecting elasticity are: nature of the commodity (necessity vs. luxury), availability of substitutes, proportion of income spent, time period, number of uses, habits, and price level.

Textbook Questions and Answers

A. Very Short Answer Questions (1 Mark)

Q1. What is utility?

Answer: Utility is the want-satisfying capacity of a commodity or service.

Q2. Define cardinal utility.

Answer: Cardinal utility is the approach which assumes that utility can be measured numerically in units called “utils”.

Q3. What is ordinal utility?

Answer: Ordinal utility is the approach according to which utility cannot be measured but can only be ranked or ordered as first, second, third preference, and so on.

Q4. Define Marginal Utility.

Answer: Marginal Utility is the additional utility derived from the consumption of one more unit of a commodity. Symbolically, MUn = TUn − TUn−1.

Q5. State the Law of Diminishing Marginal Utility.

Answer: The Law of Diminishing Marginal Utility states that as a consumer consumes more and more units of a commodity, the marginal utility derived from each successive unit goes on diminishing.

Q6. What is an indifference curve?

Answer: An indifference curve is the locus of all combinations of two goods which yield equal level of satisfaction to the consumer.

Q7. Define budget line.

Answer: The budget line shows all combinations of two goods that a consumer can purchase by spending his entire income at given market prices.

Q8. What is meant by Marginal Rate of Substitution (MRS)?

Answer: MRS is the rate at which a consumer is willing to substitute one good for another while remaining on the same indifference curve, i.e. MRSxy = ΔY/ΔX.

Q9. State the Law of Demand.

Answer: Other things remaining constant, when the price of a commodity falls, its quantity demanded rises and when the price rises, the quantity demanded falls.

Q10. What is price elasticity of demand?

Answer: Price elasticity of demand is the degree of responsiveness of quantity demanded of a good to a change in its price. Ed = −(ΔQ/Q) ÷ (ΔP/P).

B. Short Answer Questions (2-3 Marks)

Q1. Distinguish between Cardinal and Ordinal utility approaches.

Answer: (i) Cardinal approach (Marshall) assumes utility can be measured numerically in utils, while ordinal approach (Hicks-Allen) holds that utility can only be ranked. (ii) Cardinal uses Marginal Utility analysis, while ordinal uses Indifference Curve analysis. (iii) Cardinal assumes constant marginal utility of money; ordinal does not. (iv) Cardinal is considered less realistic; ordinal is more realistic.

Q2. Explain the relationship between Total Utility and Marginal Utility.

Answer: (i) When MU is positive but falling, TU increases at a diminishing rate. (ii) When MU becomes zero, TU reaches its maximum (point of saturation). (iii) When MU becomes negative, TU starts decreasing. Thus, TU is the sum of marginal utilities — TUn = ΣMU.

Q3. What is the difference between movement along the demand curve and a shift in the demand curve?

Answer: Movement along the demand curve occurs due to a change in the price of the commodity itself, leading to extension or contraction of demand. A shift in the demand curve occurs due to change in factors other than price — such as income, tastes, prices of related goods — leading to increase or decrease in demand.

Q4. Explain the concept of budget set and budget line.

Answer: The budget set is the set of all bundles of two goods that a consumer can afford with his given income at given prices. The budget line is the boundary of the budget set, showing combinations costing exactly the entire income. Its equation is Px·X + Py·Y = M, and slope = −Px/Py.

Q5. What are the factors affecting price elasticity of demand?

Answer: Major factors are: (i) Nature of the commodity — necessities are inelastic, luxuries elastic; (ii) Availability of substitutes — more substitutes mean more elastic; (iii) Proportion of income spent — small share leads to inelastic demand; (iv) Time period — demand is more elastic in the long run; (v) Number of uses — more uses make demand more elastic; (vi) Habits — habit-forming goods have inelastic demand.

Q6. Explain how a change in income affects the budget line.

Answer: A change in the consumer’s income, with prices unchanged, shifts the budget line parallel to itself. An increase in income shifts the budget line outward (to the right), expanding the budget set; a decrease shifts it inward (to the left), shrinking the budget set. The slope (−Px/Py) remains unchanged.

C. Long Answer Questions (5-6 Marks)

Q1. Explain the conditions of Consumer’s Equilibrium under the Cardinal Utility approach (single and two commodities).

Answer: A consumer is in equilibrium when he derives maximum satisfaction from the given income and prices and has no tendency to alter his consumption.

(A) Single Commodity Case: The consumer is in equilibrium when the marginal utility of the commodity equals its price multiplied by the marginal utility of money:
MUx = Px × MUm, or equivalently, MUx / Px = MUm.
If MUx/Px > MUm → consumer buys more of X (MU falls). If MUx/Px < MUm → consumer buys less. Equilibrium is reached when both are equal.

(B) Two Commodities (Law of Equi-Marginal Utility): The consumer maximises satisfaction by allocating his income between goods X and Y such that:
MUx / Px = MUy / Py = MUm.
Second-order condition: marginal utility must be diminishing. If MUx/Px > MUy/Py, the consumer reallocates expenditure from Y to X until the equality is restored.

Q2. Explain Consumer’s Equilibrium under the Ordinal (Indifference Curve) approach.

Answer: Under the ordinal approach, the consumer is in equilibrium at the point where the budget line is tangent to the highest possible indifference curve.

Conditions:
(i) First-order (necessary) condition: Slope of IC = Slope of Budget Line, i.e. MRSxy = Px/Py.
(ii) Second-order (sufficient) condition: The indifference curve must be convex to the origin at the point of tangency, i.e. MRS must be diminishing.

Explanation: If MRSxy > Px/Py, the consumer values X more than the market does and substitutes X for Y, lowering MRS. If MRSxy < Px/Py, he substitutes Y for X. Equilibrium occurs at the tangency point where MRSxy = Px/Py and the consumer cannot reach a higher IC within his budget.

Q3. Explain the main properties of an Indifference Curve.

Answer: The four main properties of an indifference curve are:

(i) Indifference curves slope downward from left to right (negative slope): Since both goods give satisfaction, an increase in one must be compensated by a decrease in the other to keep total satisfaction constant.

(ii) Indifference curves are convex to the origin: This is because of the law of diminishing Marginal Rate of Substitution. As the consumer gets more of X, he is willing to give up less and less of Y for additional units of X.

(iii) Higher indifference curve represents higher level of satisfaction: A bundle on a higher IC contains more of at least one good (and not less of the other), thus yielding greater satisfaction (monotonic preferences).

(iv) Two indifference curves never intersect each other: If they did, the point of intersection would represent two different levels of satisfaction simultaneously, which is logically impossible.

Q4. The price of a commodity falls from Rs. 10 to Rs. 8 per unit and quantity demanded rises from 100 to 140 units. Calculate the price elasticity of demand using the percentage method.

Answer: Given:
Original Price (P) = Rs. 10, New Price (P₁) = Rs. 8 → ΔP = 8 − 10 = −2.
Original Quantity (Q) = 100, New Quantity (Q₁) = 140 → ΔQ = 140 − 100 = +40.

Formula: Ed = −(ΔQ/Q) ÷ (ΔP/P) = −(ΔQ/ΔP) × (P/Q).
Ed = − (40 / −2) × (10 / 100)
= − (−20) × (0.1)
= 2.
Therefore, Ed = 2 (Relatively Elastic Demand). Since |Ed| > 1, demand is highly responsive to price changes.

Q5. Derive the demand curve of a consumer for a commodity from the price-consumption curve / explain how the demand curve is downward sloping.

Answer: The individual’s demand curve is derived from the consumer equilibrium points at different prices.

Steps of derivation: (i) Initially the consumer is at equilibrium at price P1 and demands quantity Q1. (ii) When price falls to P2 (Py and income unchanged), the budget line rotates outward, the consumer reaches a higher IC and demands a larger quantity Q2. (iii) Plotting these (P, Q) combinations on a graph gives the demand curve.

Reasons for downward slope: (a) Law of Diminishing Marginal Utility — consumer pays less for additional units; (b) Income effect — fall in price increases real income, raising demand; (c) Substitution effect — cheaper good is substituted for costlier ones; (d) New consumers enter the market; (e) Different uses — more uses become viable at lower prices. Hence the demand curve slopes downward from left to right.

Additional Practice — Multiple Choice Questions (MCQs)

Q1. Utility means:
(a) Usefulness (b) Want-satisfying capacity (c) Necessity (d) Morality
Answer: (b) Want-satisfying capacity.

Q2. Cardinal utility analysis was developed by:
(a) Hicks (b) Allen (c) Marshall (d) Samuelson
Answer: (c) Marshall.

Q3. Ordinal utility approach is associated with:
(a) Marshall (b) Hicks and Allen (c) Adam Smith (d) Keynes
Answer: (b) Hicks and Allen.

Q4. When MU is zero, TU is:
(a) Maximum (b) Minimum (c) Negative (d) Zero
Answer: (a) Maximum.

Q5. Indifference curve is convex to the origin because of:
(a) Law of demand (b) Diminishing MRS (c) Law of supply (d) Constant MU
Answer: (b) Diminishing MRS.

Q6. The slope of the budget line is:
(a) Px/Py (b) −Px/Py (c) Py/Px (d) M/Py
Answer: (b) −Px/Py.

Q7. Consumer’s equilibrium under ordinal approach occurs where:
(a) MRS > Px/Py (b) MRS < Px/Py (c) MRS = Px/Py (d) None
Answer: (c) MRS = Px/Py.

Q8. When Ed = 1, demand is:
(a) Perfectly elastic (b) Unitary elastic (c) Inelastic (d) Perfectly inelastic
Answer: (b) Unitary elastic.

Q9. A change in income leads to:
(a) Movement along demand curve (b) Shift in demand curve (c) No effect (d) Change in supply
Answer: (b) Shift in demand curve.

Q10. Two indifference curves:
(a) Always intersect (b) Never intersect (c) Are parallel (d) Are horizontal
Answer: (b) Never intersect.

Fill in the Blanks

Q1. Utility is the __________ capacity of a commodity.
Answer: want-satisfying.

Q2. Marginal Utility is measured by the formula MUn = TUn − __________.
Answer: TUn−1.

Q3. Under cardinal approach, consumer’s equilibrium for two goods requires MUx/Px = MUy/Py = __________.
Answer: MUm (Marginal Utility of Money).

Q4. Higher indifference curve represents __________ level of satisfaction.
Answer: higher.

Q5. The equation of budget line is __________.
Answer: Px·X + Py·Y = M.

True or False

Q1. Indifference curves can intersect each other.
Answer: False.

Q2. Demand curve generally slopes downward from left to right.
Answer: True.

Q3. A change in the price of the commodity itself leads to a shift in the demand curve.
Answer: False (it causes movement along the demand curve).

Q4. Necessities have inelastic demand.
Answer: True.

Q5. Cardinal utility approach assumes utility cannot be measured.
Answer: False (it assumes utility can be measured numerically).

Glossary of Key Terms

Term	Meaning
Utility	Want-satisfying capacity of a commodity.
Cardinal Utility	Utility that can be measured numerically in utils (Marshall).
Ordinal Utility	Utility that can only be ranked, not measured (Hicks-Allen).
Total Utility (TU)	Sum of utilities derived from all units consumed.
Marginal Utility (MU)	Additional utility from one more unit; MUn = TUn − TUn−1.
Law of DMU	MU falls as more units of a commodity are consumed.
Consumer’s Equilibrium	State of maximum satisfaction with no tendency to change consumption.
Indifference Curve (IC)	Locus of bundles giving equal satisfaction.
MRSxy	Rate at which X is substituted for Y on the same IC.
Budget Line	Px·X + Py·Y = M; combinations affordable spending entire income.
Budget Set	All affordable bundles (on or below the budget line).
Law of Demand	Inverse relationship between price and quantity demanded.
Movement along Demand Curve	Caused by change in own price (extension/contraction).
Shift in Demand Curve	Caused by change in non-price factors (income, tastes, etc.).
Price Elasticity of Demand	Ed = −(ΔQ/Q) ÷ (ΔP/P); responsiveness of demand to price.
Unitary Elastic Demand	Ed = 1; proportional change in Q equals proportional change in P.
Perfectly Elastic Demand	Ed = ∞; horizontal demand curve.
Perfectly Inelastic Demand	Ed = 0; vertical demand curve.

Important Formulae at a Glance

1. Marginal Utility: MUn = TUn − TUn−1.

2. Total Utility: TU = ΣMU.

3. Cardinal Equilibrium (single good): MUx / Px = MUm.

4. Cardinal Equilibrium (two goods): MUx / Px = MUy / Py = MUm.

5. Ordinal Equilibrium: MRSxy = Px / Py, with diminishing MRS.

6. Budget Line: Px·X + Py·Y = M; slope = −Px/Py.

7. Price Elasticity (Percentage Method): Ed = −(ΔQ/Q) ÷ (ΔP/P) = (ΔQ/ΔP) × (P/Q).

Conclusion: The Theory of Consumer Behaviour explains how a rational consumer makes optimal choices under the constraint of a limited budget. By understanding utility (cardinal and ordinal), indifference curves, the budget line, derivation of demand, the Law of Demand, and price elasticity, students gain the analytical foundation required for further studies in microeconomics. Master the conditions of consumer equilibrium and elasticity calculations to score full marks in your ASSEB Class 11 Economics examination. Keep practising numerical problems on elasticity and diagrammatic illustrations of indifference curves and budget lines for confident performance in the board examination.