The price elasticity of a linear demand curve is based on slope of demand curve. Slope of the demand curve is the ratio between change in quantity demanded (∆q) to change in price (∆p). So the slope of a demand curve will be different at different points. This can be explained with diagram.
1. When the demand curve cuts the 'x' axis |eD| = 0
2. When the demand curve cuts the 'y' axis |eD| = ∝
3. At the mid point of the demand curve |eD| = 1
4. Between mid point and the point where the demand curve cuts the 'X' axis |eD|<1
5. Between mid point and the point where the demand curve cuts the 'y' axis |eD|>1
