hi, my doubt is why we are mainly using sine wave for representing voltage and current wave forms instead of square,triangular,sawtooth waveforms

 

We use sine wave to represent true AC waveforms, and use square, triangular, saw for DC waveforms.

Read up on these:
DC:
http://www.allaboutcircuits.com/vol_1/index.html

AC:
http://www.allaboutcircuits.com/vol_2/index.html

 

Isn't this a conundrum? DC and Wave(form)?
Aren't these ohter waveforms considered AC, used in more specific projects, like control signals? I'm quite sure the e-book also has them in the AC Vol.

 

Yes, I checked it. Triangular, saw-tooth and other similar waveforms are considered AC, as any alternating value (either voltage or current). Now, the reason sine is so popular is that it is very easy to produce. It is generated naturaly by electric generators. It is tightly connected to the continuous circular motion of the shaft of the generator. It is much harder to construct any other waveform. Remember, anything else other than a pure sine (or cosine) is actually a superposition of many sines (or cosines) of variable magnitude and frequency. The steeper the angles of the desired waveform, the more sines are required to construct it.

 

A 'pure' sine wave is quite difficult to produce from a constant voltage/current.

This is what inverters attempt to do.

And, now-a-days, with ultra-fast switching, digital mocks analog.

You can change duty-cycle and such SO FAST that the resulting signal acts surprisingly like analog.