Re: Why a BIG variance in VOLUME between Bridge and Neck Pickups????
I think the OP is asking a theoretical question, not a practical one based on specific pickups or guitar.
The reason pickups come in sets, where an bridge pickup has a higher output than its otherwise identical neck pickup, is the reason Kam stated above.
Pickups work the way any electrical generator works. They have the same three elements: a magnetic field, conductors, and motion. Motion is the variable element, and vital. In a generator, it determines frequency. In a pickup, it determines both frequency and amplitude.
The simple fact is that at the neck position, the strings have a lot more movement than they do at the bridge position. More movement = more amplitude = hotter signal. In order to create a balanced output, pickup companies compensate for this by making the bridge pickup hotter than the neck pickup.
The corollary, of course, is that if two pickups with the same output are used, one in the neck position and one in the bridge position, then the neck pickup will have a significantly hotter signal, making a balanced output problematic.