1) The document discusses consumer equilibrium and demand curve based on the ordinal utility approach. It explains the concepts of income effect, substitution effect and price effect using diagrams. 2) The derivation of the demand curve shows the inverse relationship between price and quantity demanded through shifts in equilibrium along indifference curves as price changes. 3) Consumer surplus is defined as the excess amount a consumer is willing to pay for a good over the actual amount paid, which declines with higher consumption. It represents potential revenue that can be extracted under special conditions.

1. Unit No.2- Demand Analysis
Lesson No.-9 Consumer equilibrium and demand curve
Learning Outcomes
After reading this lesson you should-
Derive demand curve based on Ordinal Utility Approach.
Understand the relationship between the IE, SE and PE.
Understand the chief characteristics of the Ordinal Utility Approach
Analyze the concept of Consumer’s Surplus.
Introduction-
Before going to the derivation of demand curve we need
to understand the income effect, substitutions effect and price effect:
1) Income effect –
The increase or decrease in the income can be shown by the parallel shift of
the budget line.
Diagram
Qty of Y

2. A1
A
A2
B2 B B1

3. According to the diagram:
AB – original budget line A1B1
– increase in the income A2B2
– decrease in the income
The budget line shifts parallel because with increase in income a
consumer can buy more amount of goods and vice versa. Thus with the
higher level of income he can go to the higher level of IC.
Diagram
Qty of Y
A2
A1 ICC
A
B B1 B2
Qty of X
ICC is the Income Consumption Curve which shows the impact of changes in the
income on the level of consumption.
2) Substitution effect –
It is defined as the change in the equilibrium consumption of
good in response to the change in the relative prices of goods when the utility
level of the consumer remains the same. It is measured through the movement of
the consumer equilibrium along the same indifference curve.

4. Diagram
Qty of Y
A
E1
A1
E
IC 1
B B1
The substitution effect thus measures the effect of a good becoming
relatively cheaper or costlier on the basis of the quantity added of it without
making the consumer better or worse off. It always increases the demand for
relatively cheaper good and reduces the demand fro relatively costlier one.
For e.g. – In our earlier example, if the price of mangoes increase
then I may prefer to buy more of oranges and less of mangoes. In the diagram
equilibrium shifts E to E1 along the same of utility (IC1).
3) Price effect –

5. It is the change in consumption of a good because of the changes in
the price of the good.
Diagram
(P.T.O)

6. Qty of Y
A
A1 E
E2
E1
IC2
IC 1
B
M M1 B M2 B1 2
According to the diagram initial point of equilibrium is point E which
is the point of tangency between AB and IC 1. Suppose, the price of x declines it
results into shift of budget line from AB to AB2 and new equilibrium is E2. This
total change of MM2 is called a price effect. This total change can be broken up
into 2 components:
1) Substitution effect which results into the movement of the consumer
along the same IC from E to E1.
2) Income effect – It takes place because of the decline in the P x results
into more purchasing power in the hands of the consumer. This results
into parallel shift of the budget line from A 1B1 to A2B2 and shift of
equilibrium from E1 to E2. Thus,
PE = SE + IE i.e. MM2 = MM1 + M1M2

7. This is very important result yielded from ordinal approach. Such a neat
division of PE into IE and SE is possible only through the ordinal approach.
(P.T.O)

8. Derivation of Demand curve –
Diagram 1
QY
A
B B1 B2 Q X
D
Price

9. D
QX
According to the diagram, the upper panel shows the price effect and shift in
the equilibrium from E1 to E2 to E3 because of the decline in the price of x.
In the lower panel the demand curve is drawn by considering the
respective quantities of commodities from the upper panel. Thus the downward
sloping demand curve of the lower panel gives the inverse relation between
the price and the quantity demanded.
Consumer Surplus –
The dd curve can be used to estimate the amount a consumer is willing to
spend for a given level of the consumption of a commodity rather than go
without it. The excess of such an amount over what he actually pays for the
good is a surplus that accrues to the consumer for consuming the given quantity
of the good. This surplus is known as a “consumer surplus.”
For e.g. – Suppose, I am extremely thirsty and want water very desperately.
At that time I am ready to pay even Rs. 20/- for a small Bislery bottle which costs
Rs. 5/-. Here, the excess of money Rs. 15/- which I am ready to pay

10. rather that going without it is the consumer’s surplus. This consumer’s surplus
declines with consumption of hjgher quantity of the same commodity.
Diagram
PX
6
5
4
3
D
Qt
1 2 3
y
According to the diagram at price Rs. 6/- or more, the individual does
not demand any amount of x. The consumer would be willing to pay Rs. 5/- for
the first unit of x rather than go without it. Similarly, he would be willing to pay Rs.
4/- for second unit and so on.
Thus the total amount the consumer is willing to pay for two units is Rs.
9/- (= 5+4). However, he actually only Rs. 8/- (= price Rs. 4 x 2 units). Thus his
notional gain is Rs. 1/- when he consumes 2 units.
“What is the policy implication of the “consumer’s surplus” to the
manager?” Consumer’s surplus shows the potential revenue a seller or
a government can raise from the consumers of a good under very
special conditions.
Activity: -
Analyze the situation in which “artificial scarcity is created to increase
the profit” in terms of consumer’s surplus.

11. Exercises-
Q.1 Analyze the diagram given below and answer the question :
1. State the case of giffen goods. [Hint : MM 2 = MM1 + (-M2M1)]
2. From commodity x and y, which is a giffen goods?
Diagrams
Qty of Y
A

12. Exercises-
Q.1 Analyze the diagram given below and answer the question :
1. State the case of giffen goods. [Hint : MM 2 = MM1 + (-M2M1)]
2. From commodity x and y, which is a giffen goods?
Diagrams
Qty of Y
A

13. Exercises-
Q.1 Analyze the diagram given below and answer the question :
1. State the case of giffen goods. [Hint : MM 2 = MM1 + (-M2M1)]
2. From commodity x and y, which is a giffen goods?
Diagrams
Qty of Y
A