please could anybody explain me how a dc chopper works and what are its applications

 

Read this here:

http://www.eee.strath.ac.uk/~bwwilliams/Book/Chapter 13.pdf

Some of its applications i have in mind now are the switched mode power supplies (SMPS), speed control of DC motors and AC motors (inverters, they approximate a sine wave by using PWM) and class D power amplifiers.

 

Here is another link to look at:

http://encon.fke.utm.my/notes/MSc-Chopper.pdf

 

Here's the Wikipedia article - http://en.wikipedia.org/wiki/Chopper_(electronics).