According to law of demand More quantity is demanded due to fall in PRICE and less quantity is demanded due to rise in price when other things remains constant. Thus law of demand shows the negative relationship between price of a commodity and its quantity demanded. According to law of demand demand of a commodity is a function of its price.Dx = f Px here Dx = Demand of X commodity Px = Price of X commodityAssumptions of law of demand : i Price of other related goods remains constant. ii Income of the consumer remains unchanged. iii Psychological factors like habits TASTE preferences of the consumers remains constant. IV There is no EXPECTATION about the future price changes etc. Explanation of the lawAccording to law of demand shows the inverse relationship between price of concerned commodity and its quantity demanded. This inverse relationship can be seen in demand schedule and demand curve. The negative slope of the demand curve is due to the inverse relationship between price of the commodity and quantity demanded. When the price of commodity was OP the consumer was demanding OQ units of the commodity. As the price rises to OP1 the demand falls to OQ1 which is contraction in demand and as the price falls to OP2 the demand rises to OQ2 which is expansion in demand.