Types or degrees of price elasticity of demand

TYPES OR DEGREES OF PRICE ELASTICITY OF DEMAND:
    There are five types of price elasticity of demand-
1. Relatively or fairly elastic demand (ED>1)
2. Relatively or fairly inelastic demand ( ED< 1)
3.unit or unitary elastic demand (ED=  1)
4. Perfectly elastic demand ( ED= alpha)
5. Perfectly inelastic demand (ED=0)
1) Relatively elastic demand ( ED>1):
 a) Definition: If a smaller change in price causes a proportionately greater change in demand then it is called relatively elastic demand.
b) E.g.: price falls by 25℅ as a result demand rises by 50%. In the case Ed = 50÷25=2
c) Slope: The demand curve is flatter.
d) Diagram:-

  In above diagram the gap between p&p1 is less than gap between Q &Q1 because the change in price is only 25% & the change in demand is 50%.
2) Relatively or fairly inelastic demand
a) Definition:  If a greater change in price causes proportionately smaller change in demand then, it is called relatively inelastic demand.
b) E.g. price falls by 40% as a result demand rises by 20%. Here, ED= 20÷40=0.5,  ED<1
c) slope: The demand curve is steeper.
d) Diagram:

In the above diagram the gap between P & P1 is more than gap between Q&Q1 because the change in price is more than change in demand (40>20)
3) Unit or unitary elastic demand (ED=1):-
a) Definition: If change in price causes a proportionately equal change in demand, then it is called unit or unitary elastic demand.
b) E.g.: price falls by 25% as a result demand rises by 25%.
Here, ED=25%÷25%=1
(ED=1)
c) Slope: The demand curve is a  rectangular hyperbola.
d) Diagram:

In the above diagram the gap between p & p1 and Q &Q1 are equal because change in price I.e. 25% is equal to change in demand I.e. 25%
4) perfectly elastic demand ( ED=alpha):
a) Definition: At a given price ( OP)  or
 With a small fall in price ( OPI) ,if unlimited quantity of commodity is demanded then, it is called perfectly elastic demand.
b) E.g.: price falls by 5% as a result demand rises by unlimited percent. As the quantity demanded is infinite elasticity of demand is also unlimited or alpha.
c) Slope: The demand curve is a straight line parallel to X- axis or horizontal straight line.
d) Diagram:

5) perfectly inelastic demand ( ED=0):-
a) Definition: If a quantity of a commodity demanded does not change or remains fixed irrespective of change in the price then it is called perfectly inelastic demand.
b) E.g.: price falls by 25% demand rises by 0% in the case , ED= 0+25=0
ED=0
c) Slope : A demand curve is a straight line or parallel to Y-axis or vertical straight line.
d) Diagram:

In the above diagram the price may  rises from OP to OP2 or it may fall from OP to OP1 but the quantity demanded remains the same I.e. OQ only.