There is a difference between a change in supply and a change in quantity supplied. The differences are explained below.
A Change in Quantity Supplied
Change in quantity supplied can be explained as the movement long a stationary supply curve while holding other factors constant. This movement is drawn from the law of supply, which states that there is a positive relationship between price and supply while holding other factors constant. Thus, if the price moves up along the y-axis, the quantity supplied will move to the right along the x-axis. A change in quantity supplied is caused by price movements. This relationship is shown in the graph below.
An increase in price from P1 to P2 will cause an upward movement on the supply curve, as shown by the arrow. This will cause the quantity supplied to increase from Q1 to Q2.
Change in Supply
Change in supply is caused by non-price factors that influence the quantity supplied. These factors can make the supply curve to shift to the right (an increase) or to the left (a decrease). Some of the non-price factors are increases in the number of suppliers, change in technology, subsidies, and a decline in the price of raw materials, among others. A change in supply can be illustrated using a graph, as shown below.
In the graph above, favorable non-price determinants will cause the supply curve to shift from SS1 to SS2. This makes the quantity supplied to increase from Q1 to Q2. It can be noted that the price does not change. An opposite movement occurs if unfavorable non-price determinants are experienced.