Powering a circuit: electricity
1. Power vs. ground
As we mentioned before, the battery has a positive and a negative end. The convention has it that the positive side produces power (+) and the negative one is ground (-).
Just as all paths in the circuit must begin with the power side, they must all end at the ground side if you trace them along the entire length. Ground can be thought of as the “zero” side, the place where all power has been used up.