Define increase in demand. what causes …

if the other things, that is, determinants of demand other than price such as consumers’ tastes and preferences, income, price of the related goods change, the whole demand curve will change. When due to the changes in these other factors, the demand curve shifts upwards, increase in demand is said to have occurred.

Increase in demand means the consumer buys more of the good at various prices than before. For example, if the income of a consumer increases, or if the fashion for a goods increases, the consumer will buy greater quantities of the goods than before at various given prices. As a result the whole demand curve will shift upward.
In brief increase in demand occurs due to the following reasons:-

(i) The fashion for a goods increases or people’s tastes and preferences become more favourable for the good;

(ii) Consumer’s income increases.

(iii) Prices of the substitutes of the goods in question have risen.

(iv) Prices of complementary goods have fallen.