Is the alternator always running at the same speed? And is it always producing the same output?

Since it is connected to the serpentine belt is it always producing the same output? Here. Is it producing the same output when you battery is full versus if you battery is under heavy use like say you have your 1000w speaker system on, air blower on, headlight on, charging your phone, ipod, and using your fm transmitter and radar detector. Thats the best example I can give haha. Anyways thank a lot for your help. Let me know if you want any additional details. Thanks again.