What is Theory of Consumer Behaviour Class 12: Definition & Concepts

Definition and Importance of Theory of Consumer Behaviour

The Theory of Consumer Behaviour in Class 12 Economics defines how consumers decide what and how much to buy to maximise their satisfaction or utility. It assumes that consumers have limited income but unlimited wants, so they must make rational choices.

Understanding this theory is crucial because:

• It explains the demand side of the market.
• Helps predict consumer reactions to price and income changes.
• Forms the basis for demand curve derivation.

In NCERT syllabus, this theory lays the foundation for studying microeconomics and market behaviour.

Key Assumptions Underlying Consumer Behaviour Theory

The theory is based on several important assumptions:

• Rationality: Consumers aim to maximise their satisfaction.
• Limited Income: Consumers have a fixed budget to spend.
• Preferences: Consumers have clear preferences for goods.
• Utility Maximisation: Satisfaction or utility guides choices.
• Diminishing Marginal Utility: Additional units give less satisfaction.
• Perfect Knowledge: Consumers know prices and product qualities.

These assumptions simplify real-world behaviour to analyse consumer decisions effectively.

Concept of Utility: Total and Marginal Utility Explained

Utility is the satisfaction a consumer gains from consuming goods or services.

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

The relationship between TU and MU is key:

As quantity increases, MU usually decreases, illustrating the law of diminishing marginal utility.

Formula:

$$ MU = \Delta TU / \Delta Q $$

where $\Delta TU$ is change in total utility and $\Delta Q$ is change in quantity.

Budget Constraint and Consumer Choice

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

Budget Line Equation:

$$ P_x Q_x + P_y Q_y = M $$

where:

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

Consumers choose the combination of goods on or below the budget line that maximises their utility. This choice is influenced by prices and income changes.

Consumer Equilibrium: Utility Approach vs Indifference Curve Approach

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

Utility Approach:

• Consumer equilibrium occurs when the ratio of marginal utility to price is equal for all goods:

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

• Total income is spent:

$$ P_x Q_x + P_y Q_y = M $$

Indifference Curve Approach:

• Consumer equilibrium is where the budget line is tangent to the highest attainable indifference curve.
• At this point, the Marginal Rate of Substitution (MRS) equals the price ratio:

$$ MRS_{xy} = \frac{P_x}{P_y} $$

Both approaches help explain consumer choice effectively.

Worked Example: Calculating Consumer Equilibrium Using Utility Approach

Suppose a consumer buys only two goods: apples and bananas.

To find consumer equilibrium, check if:

$$ \frac{MU_{apples}}{P_{apples}} = \frac{MU_{bananas}}{P_{bananas}} $$

Calculate:

• $\frac{40}{10} = 4$
• $\frac{20}{5} = 4$

Since both ratios are equal, the consumer is in equilibrium.

If the ratios were unequal, the consumer would reallocate spending to maximise utility.