That's not how it works. There are many ways to think about it. . .but here is one. . Your common or "ground" is a reference point. You always assign it a zero potential. Everything else is referenced from that. So, your "ground" point is always zero.
I'll create a couple pics with examples of what i'm talking about . . give me a couple mins.
EDIT:
Ok, look at the attachments. In both cases, Load 1 always has 5V across it while in one, Load 2 has +12V and in the other Load 2 has -12V.
Do you see how that works. Or, in the case where the voltages across both loads are positive, the top terminal of load 1 has a potential of 17V while the bottom terminal of load 1 has a potential of 12V. So, the potential difference (what we term voltage) across that load is only 5V. (doing KVL starting from the bottom terminal of the 12V source)
Don't worry if it seems weird. . .it took me a while to accept it conceptually even though I could always prove it to be correct with circuit theory. |