windows / Tkinter - Tix - combo box - how to bind function to an event

[dudeja.rajat at gmail.com]

Hi,
I'm using Tkinter and Tix. I've created a combo box which I am able to
fill it up.
I'm want to call a function as soon as user selects some thing from
the combo box.

More precisely, I want to know how can i bind my function to this
selection event.
What this event is technically called?

Please suggest how can I do this?

-- 
Regrads,
Rajat