AC response of Triac

i was wondering if anyone could please explain what 'ac response of a triac' means as i have to do a practical course on it and my sir kinda quizzes us abt it before we do the practical.thanks

also it would be a great help if someone would please explain the waveforms of a resistive firing circuit of a SCR and of a firing circuit consisting of a capacitor and a resistor of a SCR
thankyou

 

I moved your post to a more appropriate section.

Here is a link to our Ebook section on thyristors - http://www.allaboutcircuits.com/vol_3/chpt_2/11.html. Look through it and see if you still have questions.