http://static.seton.com/media/catalog/product/Electrical-Symbol-Labels-On-A-Roll-94791-ba.gif Amperage Amperage or electrical current is the rate of charge flowing in a circuit. The units are coulombs per second or simply amperes. It is easiest to think of amperage like water flow. Both have similar units being that both are some unit per time. From the headlight circuit, it is easy to see how the current is affected by how the loads are connected by either in series or parallel. This is where Kirchhoff's Current Law comes in, KCL. The law states that sum of the currents in and out of a node is zero. A node is a connection in a circuit where electrical components connect. I(source) - I(lamp1) - I(lamp2) =  8A - 4A - 4A = 0A Its important to notice that the direction of the current going in the node determines if the current is positive or negative. In the second circuit, there can only be one current since there is only one path.     $$ When another lamp is added in parallel, the over all current is increased. This can be verified by writing a nodal equation for the currents. Notice how all the lamps are still the same brightness. This is due to each of the lamps passing same current as before. I(source) - I(lamp1) - I(lamp2) - I(lamp3) =  12A - 4A - 4A - 4A = 0A Gustav Kirchhoff, another German physicist, contributed greatly to electrical theory by developing the voltage sum rule and the current sum rule that electrical engineers and physicists use so widely. He was also able to calculate that an electric signal in a resistance-less wire travels along the wire at the speed of light. Kirchhoff also helped to developed laws in spectroscopy and thermochemistry.