http://www.allaboutcircuits.com/worksheets/thyrcir.html

Could some one please describe steps required for answering Q2?

 

In this circuit, a series resistor-capacitor network creates a phase-shifted voltage for the "gate" terminal of a power-control device known as a TRIAC. All portions of the circuit except for the RC network are ßhaded" for de-emphasis:

Calculate how many degrees of phase shift the capacitor's voltage is, compared to the total voltage across the series RC network, assuming a frequency of 60 Hz, and a 50% potentiometer setting.

Answer :EC phase shift = -76.7 degree

Please let me know involved steps; I am not from electronics - tried 1/2∏fC, but answer was something different than provided in hints!

Thanks

 

The phase shift is equal to
arc tg = R/Xc = 165K/ 39.01K = 165/39.01 = arc tg ( 4.22968) = 76.7°

http://www.wolframalpha.com/input/?i=arc+tg+(+4.22968)

 

Thanks
should we simply put a negative sign for capacitive reactance?

Just one more clarification please!

books simply say that it's 90 degree phase shift - is that statement wrongly interpreted by most of us? Or it's only me who is confused

 

Thanks
should we simply put a negative sign for capacitive reactance?

Yes we should.

books simply say that it's 90 degree phase shift - is that statement wrongly interpreted by most of us? Or it's only me who is confused

Yes you are right the books say 90 degree phase for capacitor alone.
So we have 90° phase shift between capacitor current and capacitor voltage. The capacitor current leads the voltage in capacitor.
http://forum.allaboutcircuits.com/showthread.php?p=407090#post407090
But in this Triac circuit we're talking about phase shift between input voltage and voltage across the capacitor.
http://forum.allaboutcircuits.com/showpost.php?p=312218&postcount=7