(i) Perfectly Elastic Demand (E_p = \(\infty\))
(ii) Perfectly Inelastic Demand (E_p = 0)
(iii) Relatively Elastic Demand (E_p > 1)
(iv) Relatively Inelastic Demand (E_p < 1)
(v) Unitary Elastic Demand (E_p = 1)

An indifference curve is the locus of different combinations of 2 commodities which gives the consumer the same level of satisfaction.

(i) Cardinal approach of Marshall- utility is measured by cardinal numbers such as 1,2,3
(ii) Ordinal approach of Hicks and Allen- utility can be compared or ranked or ordered such as I,II,III.

(i) Want satisfying power of a commodity is called utility.
(ii) It is measured in utils.

(i) Indifference curve must have a negative slope.
(ii) Indifference curves are convex to the origin.
(iii) Indifference curve cannot intersect
(iv) Indifference curve do not touch the horizontal or vertical axis

Total utility	Marginal utility
Increases at a diminishing rate	Goes on diminishing
Reaches maximum	Becomes zero
Diminishes	Becomes negative

Characteristics
Wants are unlimited
(i) Wants are countless and various in kinds.
(ii) When one want is satisfied another want arises.
Wants become habits
(i) When a man starts reading newspaper in the morning it becomes a habit.
Wants are satiable
(i) We can satisfy particular wants at a given time.
(ii) When one feels hungry, he takes food and that want is satisfied.
Wants are alternative
(i) There are alternative ways to satisfy a particular want (eg) idly, dosa.
Wants are competitive
(i) There is competition among wants.
(ii) So we have to choose more urgent wants and satisfy them first.
Wants are complementary
(i) Satisfaction of a particular want requires the use of more than one commodity. (eg) car and petrol.
Wants are recurring
(i) Some wants occur again and again. For ex. if we feel hungry, we take food and satisfy our want.
(ii) But after some time we again feel hungry and want food.

Introduction:
(i) The law of demand explains the direction of change in demand due to change in price.
(ii) Elasticity of demand explains the rate of change in quantity demanded due to a given change in price.
Definition:
Elasticity of demand describes the degree of responsiveness of the quantity demand for a commodity to a change in its price - Stonier and Hague.
Types:

There are four methods of measuring price elasticity of demand.
Percentage Method:
It is known as ratio method.
\(\mathrm{e_p}=\frac{\Delta \mathrm{Q}}{\Delta \mathrm{P}} \times \frac{\mathrm{P}}{\mathrm{Q}} \text { or } \frac{\% \Delta \mathrm{Q}}{\% \Delta \mathrm{P}} \text { where } \frac{\% \Delta \mathrm{Q}}{\% \Delta \mathrm{P}}=\frac{\text { Percentage change in demand }}{\text { Percentage change in price }}\)
Total Outlay Method:
Marshall suggested that this is the simplest way to decide whether demand is elastic or inelastic.
Total Revenue (Outlay) = Price x Quantity sold

Point (or) Geometrical Method:
The point elasticity in a straight line or linear demand curve is the ratio of the segments of the line to the right and to the left of the particular point.
\(Point\ elasticity=\frac{Lower\ segment\ of\ the\ demand\ curve\ below\ the\ given\ point}{Upper\ segment\ of\ the\ demand\ curve\ above\ the\ given\ point}\)