State and discuss any one component of Aggregate Demand in a two-sector economy.

Question 32 of 104

Q. State and discuss any one component of Aggregate Demand in a two-sector economy.

West Bengal WbchseCBSE Class XII Board 2022Subjective· 2mImportance★★★★★

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Concept understanding — Aggregate Demand Equilibrium

Aggregate Demand Equilibrium: The Economy's Balancing Act

Think of a seesaw. On one side sits everything people, firms, and the government want to buy. On the other side sits everything firms produce. When the seesaw is perfectly level — when total spending exactly matches total output — the economy is in equilibrium. That's the core idea.

But why should you care? Because when the seesaw tilts, real things happen. If spending exceeds output, prices rise (inflation). If output exceeds spending, factories shut down and people lose jobs. Equilibrium is the sweet spot where neither happens.

The Precise Meaning

In macroeconomics, Aggregate Demand (AD) is the total planned spending on final goods and services in an economy during a given period. Aggregate Supply (AS) is the total output firms plan to produce.

Equilibrium occurs where:

AD = AS

At this point, what buyers intend to spend exactly equals what sellers intend to produce. No unwanted inventories pile up, and no shortages force prices up. The economy is "at rest."

Y = C + I + G + (X - M)

This is the AD identity from your NCERT textbook. It tells you that total spending in the economy comes from four sources: households, firms, government, and foreigners (net of what we buy from them).

How Equilibrium Actually Works

Imagine a simple economy with only households and firms. Households earn income $Y$ from firms. They spend part of it on consumption $C$ and save the rest $S$ . Firms produce output and also invest $I$ (buying machines, building factories).

Equilibrium condition becomes:

Y = C + I

But households don't spend all their income. They save. So $C = Y - S$ . Substituting:

Y = (Y - S) + I

Which simplifies to:

S = I

Important

In equilibrium, planned savings must equal planned investment. This is the Keynesian cross condition. If people save more than firms invest, total spending falls short of output — inventories pile up, firms cut production, and income falls until savings and investment match again.

The 45° Line Diagram (Describe It)

Draw a graph with Aggregate Demand (AD) on the vertical axis and National Income (Y) on the horizontal axis.

Draw a 45° line from the origin. Every point on this line represents $AD = Y$ — the equilibrium condition.
Draw the AD curve (which is $C + I + G + (X-M)$ ). It slopes upward because as income rises, consumption rises.
Where the AD curve crosses the 45° line — that's the equilibrium point. …

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In a two-sector economy (households + firms), Aggregate Demand has two components — Consumption demand (C) and Investment demand (I): $AD = C + I$ . Taking Consumption demand as the chosen component, it is the planned household spending on final goods, given by the consumption function $C = \bar{C} + bY$ .

Aggregate Demand in a Two-Sector Economy

A two-sector economy is the simplest macroeconomic model, with only two decision-making units: households (who consume) and firms (who produce and invest). There is no government and no foreign trade. Aggregate Demand (AD) is the total planned (ex-ante) expenditure on final goods and services in the economy during a given period.

In this model AD has two components:

AD = C + I

Consumption demand (C) — planned expenditure by households on final consumer goods and services.
Investment demand (I) — planned expenditure by firms on capital goods and inventories; in the basic model it is taken as autonomous investment, $I = \bar{I}$ (independent of the current level of income).

The question asks us to state and discuss any one of these. Let us take Consumption demand (C).

The Chosen Component: Consumption Demand (C)

Consumption demand is the total planned spending by households on goods and services for current use. It is the largest and most stable component of Aggregate Demand. It is not a fixed amount — it depends primarily on the level of income, a relationship the NCERT textbook captures through the consumption function:

C = \bar{C} + bY

where:

$\bar{C}$ = autonomous consumption — the minimum consumption even when income is zero (financed by past savings or borrowing), $\bar{C} > 0$ .
$b$ = marginal propensity to consume (MPC) — the fraction of each additional rupee of income that is spent on consumption, with $0 < b < 1$ .
$Y$ = level of income.

Note

Since $0 < b < 1$ , consumption rises when income rises, but by less than the increase in income — the remainder is saved ( $S = Y - C$ ). This is the basis of the saving function and of the multiplier.

Key features of consumption demand:

It has an autonomous part ( $\bar{C}$ ), independent of income, and an induced part ( $bY$ ), which varies directly with income. …

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Q.State and discuss any one component of Aggregate Demand in a two-sector economy.

Aggregate Demand in a Two-Sector Economy

The Chosen Component: Consumption Demand (C)

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