The price elasticity of demand is not same for all the commodities. It may be high or low depending upon the numbers of factors (determining it).
Explanation with Examples:
These determining factors and their examples, which influence (affect) price elasticity of demand, in brief, are as under:
(i) Nature of Commodities. In developing countries of the world, the per capital income of the people is generally low. They spend a greater amount of their income on the purchase of necessaries of life such as wheat, milk, course cloth etc. They have to purchase these commodities whatever be their price. The demand for goods of necessities is, therefore, less elastic or inelastic. The demand for luxury goods, on the other hand is greatly elastic. For example, if the price of burger falls, its demand in the cities will go up.
(ii) Availability of Substitutes. If a good has greater number of close substitutes available in the market, the demand for the good will be greatly elastic.
For examples, if the price of Coca Cola rises in the market, people will switch over to the consumption of Pepsi Cola, which is its close substitute. So the demand for Coca Cola is elastic.
(iii) Proportion of the Income Spent on the Good. If the proportion of income spent on the purchase of a good is very small, the demand for such a good will be inelastic.
For example, if the price of matchbox or salt rises by 50%, it will not affect the consumers demand for these goods. The demand for salt and matchbox, therefore will be inelastic. On the other hand, if the price of a car rises from $6 hundred thousand to $9 hundred thousand and it takes a greater portion of the income of the consumers, its demand would fall. The demand for car is, therefore, elastic.
(iv) Time. The period of time plays an important role in shaping the demand curve. In the short run, when the consumption of a good cannot be postponed, its demand will be less elastic. In the long run if the price rise persists, people will find out methods to reduce the consumption of these goods. So the demand for a good in the long run is elastic, other things remaining constant.
For example if the price of electricity goes up, it is very difficult to cut back its consumption in the short run. However, if the rise in price persists, people will plan for substitution as gas heater, fluorescent bulbs, etc., that they use less electricity. So the demand of electricity will be greater (Ed > 1) in the long run than in the short run.
(v) Number of Uses of a Good. If a good can be put to a number of uses, its demand is greater elastic (Ed > 1).
For example, if the price of coal falls, its quantity demanded will rise considerably because demand will be rise from households, industries railways, etc.
(vi) Addition. If a product is habit forming say for example, cigarette, the rise in its price would not induce much change in demand. The demand for habit forming good is, therefore, less elastic.
(vii) Joint Demand. Joint demand occurs when demand for two goods are interdependent. If these two goods are jointly demanded, then the elasticity of demand depends upon these jointly demanded goods.
For example, with the rise in price of cars, its demand is slightly affected, then the demand for petrol will also be less elastic.