The law of demand states that there is a direct relationship between the price of a good and a demand for it. Usually the quantity demand of a good varies inversely with its price. For example, people generally buy more of a good when the price is low and buy less of it when the price is high. Ceteris Paribus can be defined as "all things being equal or constant". When there is a change in demand relation to price changes or other factors of demand, all other factors that influence demand are held constant. The purpose of a demand curve is to show the inverse relationship in quantity demand and price.
The price of good can affect quantity demand. This is cause when the price of a good goes up or down. If the price of an item goes up more potential customers will decide that the item isn't worth the price and will find a cheaper substitute. This lowers demand for the product. If the price of an item goes down more customers will be attracted by the price of the good and buy the good. this will then lead to higher demand for the product. A change in the price of a good will lead to a change in the quantity demand in the opposite direction to price change. An contraction in demand occurs when an increase in price (from QP1 to OP2) causes the quantity demand to fall (from OQ1 to OQ2). An expansion in demand occurs when a decrease in price (OP1 to OP3 causes the quantity demand to rise from OQ1 to OQ3).
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