Demand Curve: A demand curve is a graphical representation of the relationship between the price of a product and the quantity of that product demanded by consumers. The demand curve is downward sloping, indicating the inverse relationship between price and quantity demanded. It illustrates how changes in price affect the quantity demanded while holding other factors constant.

In a typical demand curve, the price is shown on the vertical axis, and the quantity demanded is shown on the horizontal axis. As the price decreases, the quantity demanded increases, and as the price increases, the quantity demanded decreases.

Law of Demand: The law of demand states that, ceteris paribus (all other factors remaining constant), there is an inverse relationship between the price of a product and the quantity demanded by consumers. This means that as the price of a product increases, the quantity demanded decreases, and vice versa.

The law of demand is based on the following behavioral patterns:

1. Income Effect: When the price of a product decreases, consumers experience an increase in their purchasing power, leading to a higher quantity demanded.
2. Substitution Effect: As the price of a product decreases, it becomes relatively cheaper compared to other goods, prompting consumers to switch from more expensive alternatives and increase the quantity demanded.

Exceptions to the Law of Demand: While the law of demand generally holds true, there are exceptions or situations where the inverse relationship between price and quantity demanded may not apply. Some common exceptions include:

1. Veblen Goods: Veblen goods are luxury goods or status symbols that defy the law of demand. As the price of Veblen goods increases, their demand may also increase due to their perceived prestige or exclusivity.
2. Giffen Goods: Giffen goods are inferior goods for which the quantity demanded increases when the price increases. This contradicts the typical behavior under the law of demand. Giffen goods are usually necessities with limited substitutes, such as staple food items.

Shifts in Demand Curve: The demand curve can shift due to changes in factors other than price. These shifts indicate a change in demand at every price level. Some factors that can cause shifts in the demand curve include:

1. Changes in Income: When consumers’ income levels change, it affects their purchasing power and, consequently, their demand for goods and services. An increase in income leads to a rightward shift in the demand curve for normal goods, indicating an increase in demand. Conversely, a decrease in income leads to a leftward shift in the demand curve.
2. Prices of Related Goods: Changes in the prices of substitute goods or complementary goods can affect the demand for a particular product. An increase in the price of a substitute good leads to a rightward shift in the demand curve, indicating an increase in demand for the original product. Conversely, an increase in the price of a complementary good leads to a leftward shift in the demand curve.
3. Consumer Preferences: Changes in consumer tastes, preferences, and trends can lead to shifts in the demand curve. If a product becomes more popular or desirable, it can result in an increase in demand, shifting the curve to the right. Conversely, a decrease in desirability or popularity leads to a decrease in demand and a leftward shift.
4. Changes in Population and Demographics: Changes in the size and composition of the population can affect demand. An increase in population generally leads to an increase in demand, shifting the curve to the right.
5. Expectations: Consumer expectations about future price changes, income fluctuations, or other factors can influence current demand. If consumers anticipate price increases in the future, it can result in an increase in current demand, shifting the curve to the right.