Economics concepts with real life examples

Cross price elasticity :
It takes place when the demand of a commodity changes in response to a change in the price of it's related commodity.

Substitute effect:
When the price of a commodity rises the demand for it's related commodity rises.

For eg : when the price of Air India tickets increased people shifted their demand towards it's substitute such as Indigo, Jet Airways, kingfisher.

Another example :
When the price of Airtel 4G increased people shifted their demand towards Jio 4G as it was offering 4G services at a much lower price.

Complementary goods:
When the price of a commodity rises the demand for it's related commodity falls.

For eg: When the price of petrol increased the demand for petrol cars decreased.

Another example :
In 2014, when the price of HP printers increased the demand for it's cartridges had decreased.

Positive Income Elasticity :
When demand for a commodity increases with the income of the consumer.

For eg:
When a customers income increases he or she travels more often than he used to travel earlier before income increased.

Another example :
When a customers income increases his/her demand for eating in reastrauants during weekends increases. Unlike eating in reastrauants once in a while.

Negative Income Elasticity :
When the demand of a commodity decreases with the increase in income of the consumer.

For eg:
When a customers income increases he or she shifts from using a nano car to Honda city.

Another example :
When a customers income increases his/her demand shifts from buying Lotto shoes to premium quality shoes such as Puma, Adidas, Nike.

Diminishing Marginal Utility :
With the continuous consumption of a commodity Marginal Utility derived from each additional unit, starts decline this is known as Law of Diminishing Marginal Utility.

For eg: In fashion industry the fashion trend remains relevant for 6-8 months after that it becomes irrelevant due to law of diminishing marginal utility.

Another example :
Going to JW Marriott and having lunch buffet, during the initial stage the consumption is more and satisfaction derived is more as the consumption continues for long the satisfaction derived starts declining due to the law of marginal utility.