hey guys i want to know about the charateristics and working of UJT , SCR
and essentially the difference between the both

 

Check the following:

All About Circuits link for SCR

Sadly, the UJT link here at All About Circuits is pending, however Wikipedia gives an elementary review of this topic.

Wikipedia link for UJT

There are also many links returned through Google, which you can use to supplement your understanding of the above topic, I recommend you look into these and post back any specific questions you may have.

Dave