When I record a song playing in my mobile via aux to my laptop, it has a different waveform from the one which I get when I drag the original source file of the track in the audacity.
Why is it so?
-Audacity 2.3.0 on Windows 8.1-
Your laptop probably doesn’t have “Aux-In”. Most laptops usually have a mono microphone input. The mic input is too sensitive for a line-level or headphone-level signal. And, the mic preamps built into laptops and soundcards tend to be low quality.
If you have a desktop computer with line-in, and if you get the levels set correctly, you can usually get good quality. But, the digital-to-analog-to-digital conversion is always imperfect, and some soundcards are noisy.
But… Don’t worry about the waveform if it sounds OK… Listen with your ears, not your eyes. 
Thanks,
But my laptop has a stereo mic input as mentioned in the specifications. And I get stereo input in audacity with two channel waveform.
May be has to do with the conversion.
Also I get little bass when recorded through aux.