Chapter 9: Consumer’s Equilibrium
A consumer is said to be in equilibrium when they maximize their satisfaction from their given income and the prices of commodities, and find no reason to change their spending pattern. There are two approaches to analyze this: Marginal Utility Analysis and Indifference Curve Analysis.
Utility Analysis
Utility refers to the want-satisfying power of a commodity. It is the imagined capability of a commodity to provide satisfaction.
- Total Utility (TU): Total satisfaction derived from the consumption of a given quantity of a commodity.
- Marginal Utility (MU): The additional satisfaction derived by consuming one more unit of a commodity. (\( MU_n = TU_n - TU_{n-1} \))
Law of Diminishing Marginal Utility (DMU)
This fundamental psychological law states that as a consumer consumes more and more standard units of a commodity continuously, the marginal utility derived from every additional unit goes on declining.
Consumer’s Equilibrium (Marginal Utility Approach)
In a single commodity case, a consumer attains equilibrium when the Marginal Utility of the good (expressed in terms of money) equals its price: $$ MU_x = P_x $$
Indifference Curve Analysis (Ordinal Utility)
An Indifference Curve (IC) is a curve showing all combinations of two goods that give the identical level of satisfaction to the consumer. Because all points on the curve yield equal satisfaction, the consumer is indifferent between them.
An Indifference Map is a set of indifference curves representing different levels of satisfaction. Higher indifference curves represent higher levels of satisfaction.
The Budget Set and Budget Line
The Budget Set represents all bundles of two goods that a consumer can purchase that cost less than or equal to the consumer’s income given prices. The Budget Line represents all combinations of two goods that exactly cost the consumer’s income. It is a straight, downward-sloping line.
Consumer’s Equilibrium (Indifference Curve Approach)
Equilibrium is reached at the point where the Budget Line is strictly tangent to the highest attainable Indifference Curve (Point E in the diagram). Conditions for equilibrium:
- Slope of IC (\(MRS_{xy}\)) = Slope of Budget Line (\(\frac{P_x}{P_y}\))
- IC must be strictly convex to the origin.
Competency-Based Questions
Case-Based Question
Q1. Suppose a pizza slice costs ₹100. Ramesh derives a Marginal Utility of 120 from the first slice, 100 from the second, and 60 from the third slice. (Assume 1 unit of utility equals ₹1). (a) At what point will Ramesh stop buying pizza slices to attain consumer equilibrium? (b) Which economic law governs the falling marginal utility values given?
Answer: (a) Ramesh will attain equilibrium and stop buying when \(MU_x = P_x\). For the 1st slice: \(MU = 120\), \(P_x = 100\) (\(MU > P_x\), he will buy). For the 2nd slice: \(MU = 100\), \(P_x = 100\) (\(MU = P_x\), he attains equilibrium). For the 3rd slice: \(MU = 60\), \(P_x = 100\) (\(MU < P_x\), he will not buy). Therefore, he will buy exactly two slices of pizza. (b) The Law of Diminishing Marginal Utility governs this behavior.
Analytical Question
Q2. An indifference curve is convex to the origin. Discuss the economic reasoning behind this property.
Answer: An indifference curve is convex toward the origin due to the operation of the Law of Diminishing Marginal Rate of Substitution (MRS). As a consumer acquires more and more units of Good X, their intensity of desire for it decreases. At the same time, the stock of Good Y with them is decreasing, making their desire for Good Y stronger. Consequently, the consumer is willing to sacrifice less and less of Good Y to obtain every additional unit of Good X. Because they sacrifice a diminishing amount of Y for an equal increase in X, the slope or MRS declines continuously, resulting in a curve that is convex to the origin.