Theory of Consumer Behaviour Class 12 Questions and Answers Explained

Understanding the Basics of Consumer Behaviour

Consumer behaviour is the study of how individuals decide to spend their available income on various goods and services to maximise satisfaction. In Class 12 Economics, the theory of consumer behaviour explains the decision-making process of consumers under constraints like income and prices.

Key concepts include:

• Utility: The satisfaction or pleasure derived from consuming a good or service.
• Total Utility (TU): The total satisfaction from consuming a certain quantity.
• Marginal Utility (MU): The additional satisfaction from consuming one more unit.

Understanding these basics is crucial for answering NCERT questions effectively.

Law of Diminishing Marginal Utility and Its Importance

The Law of Diminishing Marginal Utility states that as a consumer consumes more units of a good, the additional satisfaction gained from each extra unit decreases.

For example, if you eat one mango, your satisfaction is high, but by the fourth or fifth mango, the extra happiness reduces.

This law helps explain consumer choices and demand curves. It also assists in solving problems where you calculate total and marginal utility.

Worked example:

Notice MU decreases as units increase, illustrating the law.

Budget Constraint and Consumer Choice

Consumers face budget constraints because income is limited. The budget line shows all combinations of two goods a consumer can buy with a given income and prices.

The budget line equation is:

$$ P_x X + P_y Y = M $$

Where:

• $P_x$, $P_y$ = prices of goods X and Y
• $X$, $Y$ = quantities of goods
• $M$ = consumer’s income

Consumers aim to maximise utility within this constraint. Understanding how to draw and interpret the budget line is essential for Class 12 Economics questions.

Indifference Curves and Consumer Preferences

Indifference curves represent combinations of two goods that provide the consumer with the same level of satisfaction.

Key properties:

• Downward sloping
• Convex to the origin
• Higher curves represent higher utility

Consumers prefer points on higher indifference curves but are limited by their budget. The point where the budget line is tangent to an indifference curve shows the optimal consumption bundle.

This graphical method complements the utility approach and is important for NCERT questions.

Consumer Equilibrium: Utility and Indifference Curve Approaches

Consumer equilibrium is the point where a consumer maximises satisfaction given their budget.

Utility approach: The consumer allocates income such that the ratio of marginal utilities to prices is equal across goods:

$$ \frac{MU_x}{P_x} = \frac{MU_y}{P_y} $$

Indifference curve approach: Consumer equilibrium occurs where the budget line is tangent to the highest attainable indifference curve.

Both approaches yield the same result and are frequently asked in Class 12 NCERT questions.

Solved Example: Calculating Consumer Equilibrium

Suppose a consumer has ₹100 to spend on two goods: X and Y.

• Price of X ($P_x$) = ₹10
• Price of Y ($P_y$) = ₹20

Marginal utilities:

Find if the consumer is in equilibrium.

Solution:

Calculate $\frac{MU}{P}$ for both goods:

• For X: $\frac{40}{10} = 4$
• For Y: $\frac{60}{20} = 3$

Since $\frac{MU_x}{P_x} > \frac{MU_y}{P_y}$, the consumer should buy more of X and less of Y to maximise satisfaction.

This example shows how to apply the utility approach to consumer equilibrium.