A normal voltage or curent amplifier provides power gain...then why do we go for power amplifiers for increased power ? cant we use a cascaded amplifier stage to achieve the required power ?

 

Amplifiers can be designed for different purposes. There are different topologies which all have different characteristics. For example a Class A amplifier tries to always stay in its linear range. It makes a very poor power amplifier because it is inefficient and consumes bias currents. On the other hand a class AB push-pull amplifier does a much better job. There are several other classes of amplifiers, and you should research this topic to gain a better understanding of the issues.