Originally posted by: Eli
Originally posted by: RaynorWolfcastle
Originally posted by: Eli
Instead of everyone calling everybody else stupid, how about we actually try and learn something?
I found this thread very frustrating. I'm very interested in learning about this stuff, but most of the people that actually know aren't bothering to explain it, they're too busy calling eachother morons.
How much math do you know? Most EM theory requires that you have some pretty advanced math knowledge, ie vector calculus and complex variable math so it's not really all that accessible to the armchair scientist. We used Engineering Electromagnetic Fields and Waves by Johnk but the book is pretty dry and mathematical so I don't know if I'd recommend it to a non-engineer or anyone with a pulse for that matter .
First, can you try and explain what electromagnetic theory has to do with potential, and the OP's question?
Is my assessment of the OP's question correct? "Why can't we measure the potential voltage without completing the circuit [with a voltmeter]?"?
Think of a a river that flows down a hill, which is a good analogy for current. The current flows from the higher potential (the top of the hill) toward the bottom (the lower potential). However, you don't need a river there to know what the difference in potential energy is at those two points.
Similarly, there's no reason you'd have to "complete a circuit" to define a voltage level. A voltage is the energy possessed per unit charge. When that charge finds a path to flow to where it will have a lower energy, it creates a current, but until then, it still possesses that energy.
Edit: Like Heisenburg pointed out, a multimeter works by setting itself to a very high value of resistance and measuring the current through itself when hooked up in parallel between two points... the net effect is nearly nothing on the circuit, but its not perfect. That's just how things are done in practice.