This is the article that explains it: http://amasci.com/elect/poynt/poynt.html If the energy in a circuit is really just in the form of electromagnetic fields, what's so important about voltage? If I already know the wattage in the circuit, why should I know the potential energy per charge if the energy is flowing and not stationary? Voltage seems a useless concept if this theory is true. Also, this was stated in another topic here, but (neglecting the above) what really happens to the potential energy of a Coulomb when it passes through a circuit? Is it converted into kinetic energy? Because when electrons pass through a light bulb filament, it is the FRICTION that causes the resistor to glow, so wouldn't that be from the kinetic energy of the charges?