1) What is the difference between electromotive force (E) and voltage (V)? Based on what I've read, E is the maximum potential force, while voltage is the real one. In the case of a battery, voltage will decrease as it's being drained, but E stays the same. But how about in voltage sources, where they provide steady voltage. Is E equal to V in those? What exactly is the explanation behind this stranger Ohm's Law: E - U = R * I. I know regular Ohm's Law with just the U, so how do you explain the "expanded" version?

2) What is the difference between voltage source and current source? I understand that voltage sources offer constant voltage(allowing the components to draw however much current needed), while current sources offer constant current. How would this second source offer constant current? Can it know what voltage to push through to maintain the current? Why do we need both kinds of sources?

3) Why would you need multiple sources in a circuit? What's the difference between having two sources pushing in the same direction and them pushing in opposite directions?

4) Based on question 2, I've seen circuits with multiple voltage sources and a current source. In these circuits, the current flow is unknown and must be determined with Kirchoff. How on Earth can currrent flow opposite the voltage drop? I'm guessing since there are multiple sources, they push against each other and the stronger one sends current in the direction of ITS voltage drop.

Please explain these concepts to me. I can actually understand the calculations so far, but the explanations as to why the circuit functions that way elude me.

Thanks.