What is voltage?

Question

I am a little unclear on what voltage actually is and I am trying to find out what the physical cause for voltage is. Is it the speed of the electrons through the conductor or is it an excess of electrons on the supply side of the conductor. I somewhat understand electromagnetic induction in transformers but I can't seem to figure what the voltage is physically.

Answer 1

Voltage is, at heart, simply a way to quantify the fact that separate electric charges produce a force on each other. Similar charges repel, opposite charges attract. It is seen as a measure of the intensity of an electric field. An electric charge in an electric field will experience a force which tries to move it (an electromotive force), and it is this force which measured by voltage. Admittedly it gets more complicated than that, with distance (for instance) often thrown in, so field strength is not measured in volts, but rather volts per meter, but that's the heart of it.

Since electrons come with nicely discrete and uniform charge, and an electron which moves through a voltage of 1 volt will either require or provide a fixed, uniform amount of energy (since force times distance equals work), in some areas the electron-volt is a convenient unit of energy, but I assume you're not being confused by this.

Answer 2

If you take the hosepipe analogy, the total amount of water flowing through the pipe is charge, the amount per second is current, resistance is resistance and in order to get a flow though the resistance you need pressure. Which is the voltage.

Answer 3

Voltage is potential energy per charge. It's a function of space, so if we move one electron from a place where the potential is 2V (Location A) to where it is 1V (Location B), that takes 1 eV of work (note the sign because electrons are negative).

The reason one place is 2V and the other is 1V is because there is electric field in between, which pushes our electron and is set up by other charges that must exist somewhere. Moving the electron against this field requires the 1eV of work. Also, being potential energy, voltage is relative so we could just as easily assign Location A as 40 V and Location B as 41 V.

A battery holds its terminals at a fixed voltage, no matter what it's connected to/what it's environment is. For example, a 9V battery will always rearrange charge and push the current required to keep its terminals at 9V. That is the nature of the chemical reaction inside the battery.