In a market for apples, a consumer purchases 30 pounds when the price of apples is $1 per pound and the consumer's income is $5,000 per month

When the price of apples increases to $2 per pound, without any change in the consumer's income, he decides to purchase only 15 pounds of apples. Suppose, after a given period of time, the consumer's income falls to $3,000 per month. His consumption of apples also decreases to 10 pounds. Using a graph, illustrate the difference between change in quantity demanded and the change in demand for apples.

Initially, the consumer purchases 30 pounds at a price of $1 per pound, and his income is $5,000. Eventually, due to an increase in the price of apples, the consumer reduces his consumption by 15 pounds. Because the change in consumption is owing to a change in the price of apples, it represents a change in quantity demanded. A change in quantity demanded due to an increase in the price of apples is shown by an upward movement along the same demand curve. The change in quantity demanded is 15 units in this case.
The decrease in the consumption of apples due to a decrease in the consumer's income, the price of apples remaining unchanged, indicates a change in demand for the apples. The change in the demand for apples in this case is shown by a leftward shift of the demand curve.