Change in Quantity Demanded

Change in quantity demanded occurs when other things remaining constant, only price changes. This is what we have studied in law of demand. Here demand curve does not shift but the consumer moves from one point to another point in the same demand curve. This is also called expansion or contraction of demand. This is illustrated in following diagram.

In Fig.9, DD is the original demand curve. OP is the original price and OQ is the original quantity demanded. Now if price falls from OP to OP₁ , then quantity demanded rises from OQ to OQ₁ and the consumer moves from point M to point M1 on the same demand curve. If price rises to OP₂ then quantity demanded will fall from OQ to OQ₂. The consumer in that case will move from point M to point M₂ on the same demand curve. This is what we call change in quantity demanded.

It is important to note that shift in demand curve conforms to the change in demand and movement on the same demand curve conforms to the change in quantity demanded.